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Jimple

What is Jimple? Jimple is the intermediate representation IR of Soot, and thus SootUp. Soot's intention is to provide a simplified way to analyze JVM bytecode. JVM bytecode is stack-based, which makes it difficult for program analysis. Java source code, on the other hand, is also not quite suitable for program analysis, due to its nested structures. Therefore, Jimple aims to bring the best of both worlds, a non-stack-based and flat (non-nested) representation. For this purpose Jimple was designed as a representation of JVM bytecode which is human readable.

Info

To learn more about jimple, refer to the thesis by Raja Vallee-Rai.

It might help to visualize how the Jimple version of a Java code looks like. Have a look at the following example on the HelloWorld class.

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public class HelloWorld extends java.lang.Object
{
  public void <init>()
  {
    HelloWorld r0;
    r0 := @this: HelloWorld;
    specialinvoke r0.<java.lang.Object: void <init>()>();
    return;
  }

  public static void main(java.lang.String[])
  {
    java.lang.String[] r0;
    java.io.PrintStream $r1;

    r0 := @parameter0: java.lang.String[];
    $r1 = <java.lang.System: java.io.PrintStream out>;
    virtualinvoke $r1.<java.io.PrintStream: 
    void println(java.lang.String)>("Hello world!");
    return;
  }
}

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public class HelloWorld {

  public HelloWorld() {

  }

  public static void main(String[] var0) {
    System.out.println("Hello World!");
  }

}

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// class version 52.0 (52)
// access flags 0x21
public class analysis/HelloWorld {

// compiled from: HelloWorld.java

// access flags 0x1
public <init>()V
  L0
    LINENUMBER 4 L0
    ALOAD 0
    INVOKESPECIAL java/lang/Object.<init> ()V
  L1
    LINENUMBER 6 L1
    RETURN
  L2
    LOCALVARIABLE this Lanalysis/HelloWorld; L0 L2 0
    MAXSTACK = 1
    MAXLOCALS = 1

// access flags 0x9
public static main([Ljava/lang/String;)V
  L0
    LINENUMBER 9 L0
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    LDC "Hello World!"
    INVOKEVIRTUAL java/io/PrintStream.println (Ljava/lang/String;)V
  L1
    LINENUMBER 10 L1
    RETURN
  L2
    LOCALVARIABLE var0 [Ljava/lang/String; L0 L2 0
    MAXSTACK = 2
    MAXLOCALS = 1
}

Jimple Grammar Structure

Jimple mimics the JVMs class file structure. Therefore it is object oriented. A Single Class (or Interface) per file. Three-Address-Code which means there are no nested expressions. (nested expressions can be modeled via Locals that store intermediate calculation results.)

Class (or Interface)

A class consists of Fields and Methods. It is referenced by its ClassType. 

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public class target.exercise1.DemoClass extends java.lang.Object
{
  public void <init>()
  {
    target.exercise1.DemoClass this;
    this := @this: target.exercise1.DemoClass;
    specialinvoke this.<java.lang.Object: void <init>()>();
    return;
  }
}

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package target.exercise1;

public class DemoClass {}

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// class version 52.0 (52)
// access flags 0x21
public class target/exercise1/DemoClass {

// compiled from: DemoClass.java

// access flags 0x1
public <init>()V
  L0
    LINENUMBER 3 L0
    ALOAD 0
    INVOKESPECIAL java/lang/Object.<init> ()V
    RETURN
  L1
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L1 0
    MAXSTACK = 1
    MAXLOCALS = 1
}

Field

A Field is a piece of memory which can store a value that is accessible according to its visibility modifier. It is referenced by its FieldSignature. 

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public class target.exercise1.DemoClass extends java.lang.Object
{
  public void <init>()
  {
    target.exercise1.DemoClass this;
    this := @this: target.exercise1.DemoClass;
    specialinvoke this.<java.lang.Object: void <init>()>();
    this.<target.exercise1.DemoClass: double pi> = 3.14;
    return;
  }
}
/*
  "this.<target.exercise1.DemoClass: double pi>" is JInstanceFieldRef
*/

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package target.exercise1;

public class DemoClass {
  private final double pi = 3.14;
}

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// class version 52.0 (52)
// access flags 0x21
public class target/exercise1/DemoClass {

// compiled from: DemoClass.java

// access flags 0x12
private final D pi = 3.14

// access flags 0x1
public <init>()V
  L0
    LINENUMBER 3 L0
    ALOAD 0
    INVOKESPECIAL java/lang/Object.<init> ()V
  L1
    LINENUMBER 4 L1
    ALOAD 0
    LDC 3.14
    PUTFIELD target/exercise1/DemoClass.pi : D
    RETURN
  L2
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L2 0
    MAXSTACK = 3
    MAXLOCALS = 1
}

Method and the Body

The interesting part is a method. A method is a "piece of code" that can be executed. It is referenced by its MethodSignature and contains a StmtGraph that models the sequence of single instructions/statements (Stmts). 

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public class target.exercise1.DemoClass extends java.lang.Object
{
  public void <init>()
  {
    target.exercise1.DemoClass this;
    this := @this: target.exercise1.DemoClass;
    specialinvoke this.<java.lang.Object: void <init>()>();
    virtualinvoke this.<target.exercise1.DemoClass: 
    void demoMethod()>();
    return;
  }

  public void demoMethod()
  {
    java.io.PrintStream $stack1;
    target.exercise1.DemoClass this;

    this := @this: target.exercise1.DemoClass;
    $stack1 = <java.lang.System: java.io.PrintStream out>;

    virtualinvoke $stack1.<java.io.PrintStream: 
    void println(java.lang.String)>("Inside method.");
    return;
  }
}
/*
  "<target.exercise1.DemoClass: void demoMethod()>" 
        and "<target.exercise1.DemoClass: void <init>()>" 
        are instances of SootMethod 
*/

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package target.exercise1;

public class DemoClass {
  DemoClass(){
    demoMethod();
  }
  public void demoMethod(){
    System.out.println("Inside method.");
  }
}

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// class version 52.0 (52)
// access flags 0x21
public class target/exercise1/DemoClass {

// compiled from: DemoClass.java

// access flags 0x0
<init>()V
  L0
    LINENUMBER 5 L0
    ALOAD 0
    INVOKESPECIAL java/lang/Object.<init> ()V
  L1
    LINENUMBER 6 L1
    ALOAD 0
    INVOKEVIRTUAL target/exercise1/DemoClass.demoMethod ()V
  L2
    LINENUMBER 7 L2
    RETURN
  L3
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L3 0
    MAXSTACK = 1
    MAXLOCALS = 1

// access flags 0x1
public demoMethod()V
  L0
    LINENUMBER 10 L0
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    LDC "Inside method."
    INVOKEVIRTUAL java/io/PrintStream.println (Ljava/lang/String;)V
  L1
    LINENUMBER 11 L1
    RETURN
  L2
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L2 0
    MAXSTACK = 2
    MAXLOCALS = 1
}

Signatures

Signatures are required for identifying or referencing things across a method, such as Classes, Interfaces, Methods or Fields. Locals, on the other hand, do not need signatures, since they are referenced within method boundaries. 

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public class target.exercise1.DemoClass extends java.lang.Object
{
  public void <init>()
  {
    target.exercise1.DemoClass this;
    this := @this: target.exercise1.DemoClass;

    specialinvoke this.<java.lang.Object: void <init>()>();
    this.<target.exercise1.DemoClass: double pi> = 3.14;
    return;
  }

  public void demoMethod()
  {
    java.io.PrintStream $stack3, $stack5;
    java.lang.StringBuilder $stack4, $stack6, $stack7;
    java.lang.String $stack8;
    target.exercise1.DemoClass this;

    this := @this: target.exercise1.DemoClass;
    $stack3 = <java.lang.System: java.io.PrintStream out>;

    virtualinvoke $stack3.<java.io.PrintStream: 
      void println(java.lang.String)>("pi : 3.14");
    $stack5 = <java.lang.System: java.io.PrintStream out>;
    $stack4 = new java.lang.StringBuilder;

    specialinvoke $stack4.<java.lang.StringBuilder: void <init>()>();
    $stack6 = virtualinvoke $stack4.<java.lang.StringBuilder: 
      java.lang.StringBuilder append(java.lang.String)>
        ("pi : ");
    $stack7 = virtualinvoke $stack6.<java.lang.StringBuilder: 
      java.lang.StringBuilder append(double)>(3.1415);
    $stack8 = virtualinvoke $stack7.<java.lang.StringBuilder: 
      java.lang.String toString()>();

    virtualinvoke $stack5.<java.io.PrintStream:     
      void println(java.lang.String)>($stack8);
    return;
  }
}
/*
  For JInstanceFieldRef "this.<target.exercise1.DemoClass: double pi>" 
    signature is <target.exercise1.DemoClass: double pi>
  Similarly, we have other signatures like 
    <java.lang.Object: void <init>()>, 
    <java.io.PrintStream: void println(java.lang.String)> 
    and so on. 
*/

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package target.exercise1;

public class DemoClass {
  private final double pi = 3.14;

  public void demoMethod(){
    double localPi = 3.1415;
    System.out.println("pi : " + pi);
    System.out.println("pi : " + localPi);
  }
}

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// class version 52.0 (52)
// access flags 0x21
public class target/exercise1/DemoClass {

// compiled from: DemoClass.java

// access flags 0x12
private final D pi = 3.14

// access flags 0x1
public <init>()V
  L0
    LINENUMBER 3 L0
    ALOAD 0
    INVOKESPECIAL java/lang/Object.<init> ()V
  L1
    LINENUMBER 4 L1
    ALOAD 0
    LDC 3.14
    PUTFIELD target/exercise1/DemoClass.pi : D
    RETURN
  L2
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L2 0
    MAXSTACK = 3
    MAXLOCALS = 1

// access flags 0x1
public demoMethod()V
  L0
    LINENUMBER 6 L0
    LDC 3.1415
    DSTORE 1
  L1
    LINENUMBER 7 L1
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    LDC "pi : 3.14"
    INVOKEVIRTUAL java/io/PrintStream.println (Ljava/lang/String;)V
  L2
    LINENUMBER 8 L2
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    NEW java/lang/StringBuilder
    DUP
    INVOKESPECIAL java/lang/StringBuilder.<init> ()V
    LDC "pi : "
      INVOKEVIRTUAL java/lang/StringBuilder.append (Ljava/lang/String;)
        Ljava/lang/StringBuilder;
    DLOAD 1
    INVOKEVIRTUAL java/lang/StringBuilder.append (D)Ljava/lang/StringBuilder;
    INVOKEVIRTUAL java/lang/StringBuilder.toString ()Ljava/lang/String;
    INVOKEVIRTUAL java/io/PrintStream.println (Ljava/lang/String;)V
  L3
    LINENUMBER 9 L3
    RETURN
  L4
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L4 0
    LOCALVARIABLE localPi D L1 L4 1
    MAXSTACK = 4
    MAXLOCALS = 3
}

Trap

A Trap is a mechanism to model exceptional flow. 

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public class target.exercise1.DemoClass extends java.lang.Object
{
  public void <init>()
  {
    target.exercise1.DemoClass this;
    this := @this: target.exercise1.DemoClass;
    specialinvoke this.<java.lang.Object: void <init>()>();
    return;
  }

  public void divideExample(int, int)
  {
    int x, y, $stack4;
    java.io.PrintStream $stack5, $stack7;
    java.lang.Exception $stack6;
    target.exercise1.DemoClass this;

    this := @this: target.exercise1.DemoClass;
    x := @parameter0: int;
    y := @parameter1: int;

   label1:
      $stack5 = <java.lang.System: java.io.PrintStream out>;
      $stack4 = x / y;
      virtualinvoke $stack5.<java.io.PrintStream: void println(int)>($stack4);

   label2:
      goto label4;

   label3:
      $stack6 := @caughtexception;
      $stack7 = <java.lang.System: java.io.PrintStream out>;
      virtualinvoke $stack7.<java.io.PrintStream: 
        void println(java.lang.String)>("Exception caught");

   label4:
      return;

      catch java.lang.Exception from label1 to label2 with label3;
  }
}
/*
  By calling getTraps() method, we can get the Traip chain.
  For the above jimple code, we have the below trap:
  Trap :
  begin  : $stack5 = <java.lang.System: java.io.PrintStream out>
  end    : goto [?= return]
  handler: $stack6 := @caughtexception
*/

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package target.exercise1;

public class DemoClass {
  public void divideExample(int x, int y){
    try {
      System.out.println(x / y);
    }catch (Exception e){
      System.out.println("Exception caught");
    }
  }
}

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// class version 52.0 (52)
// access flags 0x21
public class target/exercise1/DemoClass {

// compiled from: DemoClass.java

// access flags 0x1
public <init>()V
  L0
    LINENUMBER 3 L0
    ALOAD 0
    INVOKESPECIAL java/lang/Object.<init> ()V
    RETURN
    L1
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L1 0
    MAXSTACK = 1
    MAXLOCALS = 1

// access flags 0x1
public divideExample(II)V
  TRYCATCHBLOCK L0 L1 L2 java/lang/Exception
  L0
    LINENUMBER 6 L0
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    ILOAD 1
    ILOAD 2
    IDIV
    INVOKEVIRTUAL java/io/PrintStream.println (I)V
  L1
    LINENUMBER 9 L1
    GOTO L3
  L2
    LINENUMBER 7 L2
    FRAME SAME1 java/lang/Exception
    ASTORE 3
  L4
    LINENUMBER 8 L4
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    LDC "Exception caught"
    INVOKEVIRTUAL java/io/PrintStream.println (Ljava/lang/String;)V
  L3
    LINENUMBER 10 L3
    FRAME SAME
    RETURN
  L5
    LOCALVARIABLE e Ljava/lang/Exception; L4 L3 3
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L5 0
    LOCALVARIABLE x I L0 L5 1
    LOCALVARIABLE y I L0 L5 2
    MAXSTACK = 3
    MAXLOCALS = 4
}

Stmt

The main piece of Jimple is a Statement (Stmt). Stmts represent that can be executed by the JVM.

Branching Statements

A BranchingStmt's job is to model the flow between Stmts.

JGotoStmt

for unconditional flow. 

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public class target.exercise1.DemoClass extends java.lang.Object
{
  public void <init>()
  {
    target.exercise1.DemoClass this;
    this := @this: target.exercise1.DemoClass;
    specialinvoke this.<java.lang.Object: void <init>()>();
    return;
  }
  public static void sampleMethod()
  {
    int i;
    i = 0;

    label1:
      if i >= 5 goto label3;
      if i != 3 goto label2;
      goto label3;

    label2:
      i = i + 1;
      goto label1;

    label3:
      return;
  }
}
/*
  Here for statements "goto label3;" and "goto label1;", 
  we have two instances of JGotoStmt : 
    "goto[?=return]" and "goto[?=(branch)]".
*/

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package target.exercise1;

public class DemoClass {
  public static void sampleMethod(){
    label1:
    for (int i = 0; i < 5; i++){
      if(i == 3){
        break label1;
      }
    }
  }
}

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// class version 52.0 (52)
// access flags 0x21
public class target/exercise1/DemoClass {

// compiled from: DemoClass.java

// access flags 0x1
public <init>()V
  L0
    LINENUMBER 3 L0
    ALOAD 0
    INVOKESPECIAL java/lang/Object.<init> ()V
    RETURN
  L1
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L1 0
    MAXSTACK = 1
    MAXLOCALS = 1

// access flags 0x9
public static sampleMethod()V
  L0
    LINENUMBER 6 L0
    ICONST_0
    ISTORE 0
  L1
    FRAME APPEND [I]
    ILOAD 0
    ICONST_5
    IF_ICMPGE L2
  L3
    LINENUMBER 7 L3
    ILOAD 0
    ICONST_3
    IF_ICMPNE L4
  L5
    LINENUMBER 8 L5
    GOTO L2
  L4
    LINENUMBER 6 L4
    FRAME SAME
    IINC 0 1
    GOTO L1
  L2
    LINENUMBER 11 L2
    FRAME CHOP 1
    RETURN
    LOCALVARIABLE i I L1 L2 0
    MAXSTACK = 2
    MAXLOCALS = 1
}
JIfStmt

for conditional flow depending on boolean Expression (AbstractConditionExpr) so they have two successor Stmt's. 

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public class target.exercise1.DemoClass extends java.lang.Object
{
   public void <init>()
  {
    target.exercise1.DemoClass this;
    this := @this: target.exercise1.DemoClass;
    specialinvoke this.<java.lang.Object: void <init>()>();
    return;
  }

  public static void sampleMethod(int)
  {
    int x, $stack1;
    java.io.PrintStream $stack2, $stack3;

    x := @parameter0: int;

    $stack1 = x % 2;
    if $stack1 != 0 goto label1;

    $stack3 = <java.lang.System: java.io.PrintStream out>;
    virtualinvoke $stack3.<java.io.PrintStream: 
      void println(java.lang.String)>("Even");
    goto label2;

    label1:
      $stack2 = <java.lang.System: java.io.PrintStream out>;
      virtualinvoke $stack2.<java.io.PrintStream: 
        void println(java.lang.String)>("Odd");

    label2:
      return;
  }
}
/*
  For statement "if $stack1 != 0 goto label1;", 
  we have an instance of JIfStmt :
    "if $stack1 != 0 goto $stack2 
        = <java.lang.System:java.io.PrintStream out>".
*/

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package target.exercise1;

public class DemoClass {
  public static void sampleMethod(int x){
    if(x % 2 == 0){
      System.out.println("Even");
    }else{
      System.out.println("Odd");
    }
  }
}

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// class version 52.0 (52)
// access flags 0x21
public class target/exercise1/DemoClass {

// compiled from: DemoClass.java

// access flags 0x1
public <init>()V
  L0
    LINENUMBER 3 L0
    ALOAD 0
    INVOKESPECIAL java/lang/Object.<init> ()V
    RETURN
  L1
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L1 0
    MAXSTACK = 1
    MAXLOCALS = 1

// access flags 0x9
public static sampleMethod(I)V
  L0
    LINENUMBER 5 L0
    ILOAD 0
    ICONST_2
    IREM
    IFNE L1
  L2
    LINENUMBER 6 L2
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    LDC "Even"
    INVOKEVIRTUAL java/io/PrintStream.println (Ljava/lang/String;)V
    GOTO L3
  L1
    LINENUMBER 8 L1
    FRAME SAME
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    LDC "Odd"
    INVOKEVIRTUAL java/io/PrintStream.println (Ljava/lang/String;)V
  L3
    LINENUMBER 10 L3
    FRAME SAME
    RETURN
  L4
    LOCALVARIABLE x I L0 L4 0
    MAXSTACK = 2
    MAXLOCALS = 1
}
JSwitchStmt

for conditional flow that behaves like a switch-case. It has #numberOfCaseLabels+1 (for default) successor Stmt's.

All other Stmts are not manipulating the flow, which means they have a single successor Stmt as long as they are not exiting the flow inside a method. 

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public class target.exercise1.DemoClass extends java.lang.Object
{
  public void <init>()
  {
    target.exercise1.DemoClass this;
    this := @this: target.exercise1.DemoClass;
    specialinvoke this.<java.lang.Object: void <init>()>();
    return;
  }

  public void switchExample(int)
  {
    int x;
    java.io.PrintStream $stack2, $stack3, $stack4;
    target.exercise1.DemoClass this;

    this := @this: target.exercise1.DemoClass;
    x := @parameter0: int;

    lookupswitch(x)
    {
      case 1: goto label1;
      case 2: goto label2;
      default: goto label3;
    };

    label1:
      $stack3 = <java.lang.System: java.io.PrintStream out>;
      virtualinvoke $stack3.<java.io.PrintStream: 
        void println(java.lang.String)>("Input 1");
      goto label4;

    label2:
      $stack2 = <java.lang.System: java.io.PrintStream out>;
      virtualinvoke $stack2.<java.io.PrintStream: 
        void println(java.lang.String)>("Input 2");
      goto label4;

    label3:
      $stack4 = <java.lang.System: java.io.PrintStream out>;
      virtualinvoke $stack4.<java.io.PrintStream: 
        void println(java.lang.String)>("Input more than 2");

    label4:
      return;
  }
}
/*
  Here for below statement:
    lookupswitch(x)
      {
        case 1: goto label1;
        case 2: goto label2;
        default: goto label3;
      };

  we have an instance of JLookupSwitchStmt :
    lookupswitch(x) 
      {     
        case 1: goto $stack3 
                        = <java.lang.System: java.io.PrintStream out>;     
        case 2: goto $stack2 
                        = <java.lang.System: java.io.PrintStream out>;     
        default: goto $stack4 
                        = <java.lang.System: java.io.PrintStream out>; 
      }
*/

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package target.exercise1;

public class DemoClass {
  public void switchExample(int x){
    switch (x){
      case 1:
        System.out.println("Input 1");
        break;

      case 2:
        System.out.println("Input 2");
        break;

      default:
        System.out.println("Input more than 2");
        break;

    }
  }
}

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// class version 52.0 (52)
// access flags 0x21
public class target/exercise1/DemoClass {

// compiled from: DemoClass.java

// access flags 0x1
public <init>()V
  L0
    LINENUMBER 3 L0
    ALOAD 0
    INVOKESPECIAL java/lang/Object.<init> ()V
    RETURN
  L1
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L1 0
    MAXSTACK = 1
    MAXLOCALS = 1

// access flags 0x1
public switchExample(I)V
  L0
    LINENUMBER 5 L0
    ILOAD 1
    LOOKUPSWITCH
    1: L1
    2: L2
    default: L3
  L1
    LINENUMBER 7 L1
    FRAME SAME
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    LDC "Input 1"
    INVOKEVIRTUAL java/io/PrintStream.println (Ljava/lang/String;)V
  L4
    LINENUMBER 8 L4
    GOTO L5
  L2
    LINENUMBER 11 L2
    FRAME SAME
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    LDC "Input 2"
    INVOKEVIRTUAL java/io/PrintStream.println (Ljava/lang/String;)V
  L6
    LINENUMBER 12 L6
    GOTO L5
  L3
    LINENUMBER 15 L3
    FRAME SAME
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    LDC "Input more than 2"
    INVOKEVIRTUAL java/io/PrintStream.println (Ljava/lang/String;)V
  L5
    LINENUMBER 19 L5
    FRAME SAME
    RETURN
  L7
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L7 0
    LOCALVARIABLE x I L0 L7 1
    MAXSTACK = 2
    MAXLOCALS = 2
}
JReturnStmt & JReturnVoidStmt

They end the execution/flow inside the current method and return (a value) to its caller. 

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public class target.exercise1.DemoClass extends java.lang.Object
{
  public void <init>()
  {
    target.exercise1.DemoClass this;
    this := @this: target.exercise1.DemoClass;
    specialinvoke this.<java.lang.Object: void <init>()>();
    return;
  }

  public int increment(int)
  {
    int x, $stack2;
    target.exercise1.DemoClass this;

    this := @this: target.exercise1.DemoClass;
    x := @parameter0: int;

    $stack2 = x + 1;
    return $stack2;
  }

  public void print()
  {
    java.io.PrintStream $stack1;
    target.exercise1.DemoClass this;

    this := @this: target.exercise1.DemoClass;
    $stack1 = <java.lang.System: java.io.PrintStream out>;
    virtualinvoke $stack1.<java.io.PrintStream: 
      void println(java.lang.String)>("Inside method print");
    return;
  }
}
/*
  "return $stack2" is JReturnStmt.
  "return" is JReturnVoidStmt.
*/

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package target.exercise1;

public class DemoClass {
  public int increment(int x){
    return x + 1;
  }
  public void print(){
    System.out.println("Inside method print");
  }
}

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// class version 52.0 (52)
// access flags 0x21
public class target/exercise1/DemoClass {

// compiled from: DemoClass.java

// access flags 0x1
public <init>()V
  L0
    LINENUMBER 3 L0
    ALOAD 0
    INVOKESPECIAL java/lang/Object.<init> ()V
    RETURN
  L1
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L1 0
    MAXSTACK = 1
    MAXLOCALS = 1

// access flags 0x1
public increment(I)I
  L0
    LINENUMBER 5 L0
    ILOAD 1
    ICONST_1
    IADD
    IRETURN
  L1
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L1 0
    LOCALVARIABLE x I L0 L1 1
    MAXSTACK = 2
    MAXLOCALS = 2

// access flags 0x1
public print()V
  L0
    LINENUMBER 8 L0
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    LDC "Inside method print"
    INVOKEVIRTUAL java/io/PrintStream.println (Ljava/lang/String;)V
  L1
    LINENUMBER 9 L1
    RETURN
  L2
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L2 0
    MAXSTACK = 2
    MAXLOCALS = 1
}
JThrowStmt

Ends the execution inside the current Method if the thrown exception is not caught by a Trap, which redirects the execution to an exceptionhandler. 

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public class target.exercise1.DemoClass extends java.lang.Object
{
  public void <init>()
  {
    target.exercise1.DemoClass this;
    this := @this: target.exercise1.DemoClass;
    specialinvoke this.<java.lang.Object: void <init>()>();
    return;
  }

  public void divideExample(int, int)
  {
    int y, x, $stack6;
    java.lang.StringBuilder $stack3, $stack5, $stack7;
    java.io.PrintStream $stack4;
    java.lang.String $stack8;
    java.lang.RuntimeException $stack9;
    target.exercise1.DemoClass this;

    this := @this: target.exercise1.DemoClass;
    x := @parameter0: int;
    y := @parameter1: int;

    if y != 0 goto label1;

    $stack9 = new java.lang.RuntimeException;
    specialinvoke $stack9.<java.lang.RuntimeException: 
      void <init>(java.lang.String)>("Divide by zero error");
    throw $stack9;

    label1:
      $stack4 = <java.lang.System: java.io.PrintStream out>;
      $stack3 = new java.lang.StringBuilder;
      specialinvoke $stack3.<java.lang.StringBuilder: void <init>()>();

      $stack5 = virtualinvoke $stack3.<java.lang.StringBuilder: 
        java.lang.StringBuilder append(java.lang.String)>("Divide result : ");
      $stack6 = x / y;
      $stack7 = virtualinvoke $stack5.<java.lang.StringBuilder: 
        java.lang.StringBuilder append(int)>($stack6);
      $stack8 = virtualinvoke $stack7.<java.lang.StringBuilder: 
        java.lang.String toString()>();

      virtualinvoke $stack4.<java.io.PrintStream: 
        void println(java.lang.String)>($stack8);
      return;
  }
}
/*
  "throw $stack9" is JThrowStmt.
*/

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package target.exercise1;

public class DemoClass {
  public void divideExample(int x, int y){
    if(y == 0){
      throw new RuntimeException("Divide by zero error");
    }
    System.out.println("Divide result : " + x / y);
  }
}

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// class version 52.0 (52)
// access flags 0x21
public class target/exercise1/DemoClass {

// compiled from: DemoClass.java

// access flags 0x1
public <init>()V
  L0
    LINENUMBER 3 L0
    ALOAD 0
    INVOKESPECIAL java/lang/Object.<init> ()V
    RETURN
  L1
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L1 0
    MAXSTACK = 1
    MAXLOCALS = 1

// access flags 0x1
public divideExample(II)V
  L0
    LINENUMBER 5 L0
    ILOAD 2
    IFNE L1
  L2
    LINENUMBER 6 L2
    NEW java/lang/RuntimeException
    DUP
    LDC "Divide by zero error"
    INVOKESPECIAL java/lang/RuntimeException.<init> 
      (Ljava/lang/String;)V
    ATHROW
  L1
    LINENUMBER 8 L1
    FRAME SAME
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    NEW java/lang/StringBuilder
    DUP
    INVOKESPECIAL java/lang/StringBuilder.<init> ()V
    LDC "Divide result : "
    INVOKEVIRTUAL java/lang/StringBuilder.append 
      (Ljava/lang/String;)Ljava/lang/StringBuilder;
    ILOAD 1
    ILOAD 2
    IDIV
    INVOKEVIRTUAL java/lang/StringBuilder.append 
      (I)Ljava/lang/StringBuilder;
    INVOKEVIRTUAL java/lang/StringBuilder.toString 
      ()Ljava/lang/String;
    INVOKEVIRTUAL java/io/PrintStream.println 
      (Ljava/lang/String;)V
  L3
    LINENUMBER 9 L3
    RETURN
  L4
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L4 0
    LOCALVARIABLE x I L0 L4 1
    LOCALVARIABLE y I L0 L4 2
    MAXSTACK = 4
    MAXLOCALS = 3
}
JInvokeStmt

transfers the control flow to another method until the called method returns. 

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public class target.exercise1.DemoClass extends java.lang.Object
{
  public void <init>()
  {
    target.exercise1.DemoClass this;
    this := @this: target.exercise1.DemoClass;
    specialinvoke this.<java.lang.Object: void <init>()>();
    return;
  }

  public void print(int)
  {
    target.exercise1.DemoClass this;
    int x, a;
    java.io.PrintStream $stack4, $stack6;

    this := @this: target.exercise1.DemoClass;
    x := @parameter0: int;

    a = virtualinvoke this.<target.exercise1.DemoClass: 
      int increment(int)>(x);
    $stack4 = <java.lang.System: java.io.PrintStream out>;
    virtualinvoke $stack4.<java.io.PrintStream: 
      void println(int)>(a);

    a = virtualinvoke this.<target.exercise1.DemoClass: 
      int increment(int)>(a);
    $stack6 = <java.lang.System: java.io.PrintStream out>;
    virtualinvoke $stack6.<java.io.PrintStream: 
      void println(int)>(a);

    return;
  }

  public int increment(int)
  {
    int x, $stack2;
    target.exercise1.DemoClass this;

    this := @this: target.exercise1.DemoClass;
    x := @parameter0: int;

    $stack2 = x + 1;
    return $stack2;
  }
}
/*
  "specialinvoke this.<java.lang.Object: void <init>()>()", 
  "virtualinvoke this.<target.exercise1.DemoClass: int increment(int)>(x)", 
  "virtualinvoke this.<target.exercise1.DemoClass: int increment(int)>(a)" 
    are JInvokeStmts.
*/

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package target.exercise1;

public class DemoClass {
  public void print(int x){
    int a = increment(x);
    System.out.println(a);
    a = increment(a);
    System.out.println(a);
  }
  public int increment(int x){
    return x + 1;
  }
}

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// class version 52.0 (52)
// access flags 0x21
public class target/exercise1/DemoClass {

// compiled from: DemoClass.java

// access flags 0x1
public <init>()V
  L0
    LINENUMBER 3 L0
    ALOAD 0
    INVOKESPECIAL java/lang/Object.<init> ()V
    RETURN
  L1
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L1 0
    MAXSTACK = 1
    MAXLOCALS = 1

// access flags 0x1
public print(I)V
  L0
    LINENUMBER 5 L0
    ALOAD 0
    ILOAD 1
    INVOKEVIRTUAL target/exercise1/DemoClass.increment (I)I
    ISTORE 2
  L1
    LINENUMBER 6 L1
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    ILOAD 2
    INVOKEVIRTUAL java/io/PrintStream.println (I)V
  L2
    LINENUMBER 7 L2
    ALOAD 0
    ILOAD 2
    INVOKEVIRTUAL target/exercise1/DemoClass.increment (I)I
    ISTORE 2
  L3
    LINENUMBER 8 L3
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    ILOAD 2
    INVOKEVIRTUAL java/io/PrintStream.println (I)V
  L4
    LINENUMBER 9 L4
    RETURN
  L5
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L5 0
    LOCALVARIABLE x I L0 L5 1
    LOCALVARIABLE a I L1 L5 2
    MAXSTACK = 2
    MAXLOCALS = 3

// access flags 0x1
public increment(I)I
  L0
    LINENUMBER 11 L0
    ILOAD 1
    ICONST_1
    IADD
    IRETURN
  L1
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L1 0
    LOCALVARIABLE x I L0 L1 1
    MAXSTACK = 2
    MAXLOCALS = 2
}
JAssignStmt

assigns a Value from the right hand-side to the left hand-side. Left hand-side of an assignment can be a Local referencing a variable (i.e. a Local) or a FieldRef referencing a Field. Right hand-side of an assignment can be an expression (Expr), a Local, a FieldRef or a Constant. 

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public class target.exercise1.DemoClass extends java.lang.Object
{
  public void <init>()
  {
    target.exercise1.DemoClass this;
    this := @this: target.exercise1.DemoClass;
    specialinvoke this.<java.lang.Object: void <init>()>();
    this.<target.exercise1.DemoClass: int counter> = 0;
    return;
  }

  public int updateCounter()
  {
    target.exercise1.DemoClass this;
    int $stack1, $stack2, $stack3;

    this := @this: target.exercise1.DemoClass;

    $stack1 = this.<target.exercise1.DemoClass: int counter>;
    $stack2 = $stack1 + 1;
    this.<target.exercise1.DemoClass: int counter> = $stack2;
    $stack3 = this.<target.exercise1.DemoClass: int counter>;

    return $stack3;
  }
}
/*
  "this.<target.exercise1.DemoClass: int counter> = 0", 
  "$stack1 = this.<target.exercise1.DemoClass: int counter>",
  "$stack2 = $stack1 + 1"
  "this.<target.exercise1.DemoClass: int counter> = $stack2"
  "$stack3 = this.<target.exercise1.DemoClass: int counter>"
    are JAssignStmts.
*/

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package target.exercise1;

public class DemoClass {
  private int counter = 0;
  public int updateCounter(){
    counter = counter + 1;
    return counter;
  }
}

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// class version 52.0 (52)
// access flags 0x21
public class target/exercise1/DemoClass {

// compiled from: DemoClass.java

// access flags 0x2
private I counter

// access flags 0x1
public <init>()V
  L0
    LINENUMBER 3 L0
    ALOAD 0
    INVOKESPECIAL java/lang/Object.<init> ()V
  L1
    LINENUMBER 4 L1
    ALOAD 0
    ICONST_0
    PUTFIELD target/exercise1/DemoClass.counter : I
    RETURN
  L2
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L2 0
    MAXSTACK = 2
    MAXLOCALS = 1

// access flags 0x1
public updateCounter()I
  L0
    LINENUMBER 6 L0
    ALOAD 0
    ALOAD 0
    GETFIELD target/exercise1/DemoClass.counter : I
    ICONST_1
    IADD
    PUTFIELD target/exercise1/DemoClass.counter : I
  L1
    LINENUMBER 7 L1
    ALOAD 0
    GETFIELD target/exercise1/DemoClass.counter : I
    IRETURN
  L2
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L2 0
    MAXSTACK = 3
    MAXLOCALS = 1
}
JIdentityStmt

is semantically like the JAssignStmt and handles assignments of IdentityRef's to make implicit assignments explicit into the StmtGraph. 

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public class target.exercise1.DemoClass extends java.lang.Object
{
  public void <init>()
  {
    target.exercise1.DemoClass this;
    this := @this: target.exercise1.DemoClass;
    specialinvoke this.<java.lang.Object: void <init>()>();
    return;
  }

  public void DemoClass(int)
  {
    target.exercise1.DemoClass this;
    int counter;

    this := @this: target.exercise1.DemoClass;
    counter := @parameter0: int;
    this.<target.exercise1.DemoClass: int counter> = counter;
    return;
  }
}
/*
  "this := @this: target.exercise1.DemoClass" and 
    "counter := @parameter0: int" are JIdentityStmts
*/

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package target.exercise1;

public class DemoClass {
  private int counter;
  public void DemoClass(int counter){
    this.counter = counter;
  }
}

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// class version 52.0 (52)
// access flags 0x21
public class target/exercise1/DemoClass {

// compiled from: DemoClass.java

// access flags 0x2
private I counter

// access flags 0x1
public <init>()V
  L0
    LINENUMBER 3 L0
    ALOAD 0
    INVOKESPECIAL java/lang/Object.<init> ()V
    RETURN
  L1
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L1 0
    MAXSTACK = 1
    MAXLOCALS = 1

// access flags 0x1
public DemoClass(I)V
  L0
    LINENUMBER 6 L0
    ALOAD 0
    ILOAD 1
    PUTFIELD target/exercise1/DemoClass.counter : I
  L1
    LINENUMBER 7 L1
    RETURN
  L2
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L2 0
    LOCALVARIABLE counter I L0 L2 1
    MAXSTACK = 2
    MAXLOCALS = 2
}
JEnterMonitorStmt & JExitMonitorStmt

marks synchronized blocks of code from JEnterMonitorStmt to JExitMonitorStmt. 

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public class target.exercise1.DemoClass extends java.lang.Object
{
  public void <init>()
  {
    target.exercise1.DemoClass this;
    this := @this: target.exercise1.DemoClass;
    specialinvoke this.<java.lang.Object: void <init>()>();
    this.<target.exercise1.DemoClass: int counter> = 0;
    return;
  }

  public int updateCounter()
  {
    target.exercise1.DemoClass this;
    int $stack4, $stack5, $stack7;
    java.lang.Throwable $stack8;

    this := @this: target.exercise1.DemoClass;

    entermonitor this;

    label1:
      $stack4 = this.<target.exercise1.DemoClass: int counter>;
      $stack5 = $stack4 + 1;
      this.<target.exercise1.DemoClass: int counter> = $stack5;

      exitmonitor this;

    label2:
      goto label5;

    label3:
      $stack8 := @caughtexception;

      exitmonitor this;

    label4:
      throw $stack8;

    label5:
      $stack7 = this.<target.exercise1.DemoClass: int counter>;
      return $stack7;

      catch java.lang.Throwable from label1 to label2 with label3;
      catch java.lang.Throwable from label3 to label4 with label3;
  }
}
/*
  "entermonitor this" is JEnterMonitorStmt.
  "exitmonitor this" is JExitMonitorStmt.
*/

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package target.exercise1;

public class DemoClass {
  private int counter = 0;
  public int updateCounter(){
    synchronized (this) {
      counter = counter + 1;
    }
    return counter;
  }
}

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// class version 52.0 (52)
// access flags 0x21
public class target/exercise1/DemoClass {

// compiled from: DemoClass.java

// access flags 0x2
private I counter

// access flags 0x1
public <init>()V
  L0
    LINENUMBER 3 L0
    ALOAD 0
    INVOKESPECIAL java/lang/Object.<init> ()V
  L1
    LINENUMBER 4 L1
    ALOAD 0
    ICONST_0
    PUTFIELD target/exercise1/DemoClass.counter : I
    RETURN
  L2
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L2 0
    MAXSTACK = 2
    MAXLOCALS = 1

// access flags 0x1
public updateCounter()I
    TRYCATCHBLOCK L0 L1 L2 null
    TRYCATCHBLOCK L2 L3 L2 null
  L4
    LINENUMBER 6 L4
    ALOAD 0
    DUP
    ASTORE 1
    MONITORENTER
  L0
    LINENUMBER 7 L0
    ALOAD 0
    ALOAD 0
    GETFIELD target/exercise1/DemoClass.counter : I
    ICONST_1
    IADD
    PUTFIELD target/exercise1/DemoClass.counter : I
  L5
    LINENUMBER 8 L5
    ALOAD 1
    MONITOREXIT
  L1
    GOTO L6
  L2
    FRAME FULL [target/exercise1/DemoClass java/lang/Object] 
      [java/lang/Throwable]
    ASTORE 2
    ALOAD 1
    MONITOREXIT
  L3
    ALOAD 2
    ATHROW
  L6
    LINENUMBER 9 L6
    FRAME CHOP 1
    ALOAD 0
    GETFIELD target/exercise1/DemoClass.counter : I
    IRETURN
  L7
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L4 L7 0
    MAXSTACK = 3
    MAXLOCALS = 3
}
JRetStmt
JBreakpointStmt

models a Breakpoint set by a Debugger (usually not relevant for static analyses)

Immediate

An Immediate has a given Type and consists of a Local ("a Variable", "Something that contains a Value") or a Constant ("Something that is a Value").

Type

VoidType 

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public class target.exercise1.DemoClass extends java.lang.Object
{
  public void <init>()
  {
  target.exercise1.DemoClass this;
  this := @this: target.exercise1.DemoClass;
  specialinvoke this.<java.lang.Object: void <init>()>();
  return;
  }

  public void voidMethod()
  {
  java.io.PrintStream $stack1;
  target.exercise1.DemoClass this;
  this := @this: target.exercise1.DemoClass;
  $stack1 = <java.lang.System: java.io.PrintStream out>;
  virtualinvoke $stack1.<java.io.PrintStream: 
      void println(java.lang.String)>("In voidMethod().");
  return;
  }
}
/*
  For the SootMethod - <target.exercise1.DemoClass: void voidMethod()>, 
    returnType is instance of VoidType.
*/

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package target.exercise1;

public class DemoClass {
  public void voidMethod(){
  System.out.println("In voidMethod().");
  }
}

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// class version 52.0 (52)
// access flags 0x21
public class target/exercise1/DemoClass {

// compiled from: DemoClass.java

// access flags 0x1
public <init>()V
  L0
    LINENUMBER 3 L0
    ALOAD 0
    INVOKESPECIAL java/lang/Object.<init> ()V
    RETURN
  L1
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L1 0
    MAXSTACK = 1
    MAXLOCALS = 1

// access flags 0x1
public voidMethod()V
  L0
    LINENUMBER 5 L0
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    LDC "In voidMethod()."
    INVOKEVIRTUAL java/io/PrintStream.println (Ljava/lang/String;)V
  L1
    LINENUMBER 6 L1
    RETURN
  L2
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L2 0
    MAXSTACK = 2
    MAXLOCALS = 1
}

PrimaryType

BooleanType, ByteType, CharType, ShortType, IntType, LongType, DoubleType, FloatType 

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public class target.exercise1.DemoClass extends java.lang.Object
{
  public void <init>()
  {
      target.exercise1.DemoClass this;
      this := @this: target.exercise1.DemoClass;
      specialinvoke this.<java.lang.Object: void <init>()>();
      return;
  }


  public void display()
  {
      java.io.PrintStream $stack11, $stack13, $stack15, 
        $stack17, $stack19, $stack21, $stack23, $stack25;
      int $stack12, $stack14, $stack16, $stack18;
      long $stack20;
      double $stack22;
      float $stack24;
      target.exercise1.DemoClass this;
      boolean $stack26;

      this := @this: target.exercise1.DemoClass;

      $stack11 = <java.lang.System: java.io.PrintStream out>;

      goto label1;

   label1:
      $stack26 = 0;
      virtualinvoke $stack11.<java.io.PrintStream: 
        void println(boolean)>($stack26);

      $stack13 = <java.lang.System: java.io.PrintStream out>;
      $stack12 = 127 - 1;
      virtualinvoke $stack13.<java.io.PrintStream: 
        void println(int)>($stack12);

      $stack15 = <java.lang.System: java.io.PrintStream out>;
      $stack14 = 97 + 1;
      virtualinvoke $stack15.<java.io.PrintStream: 
        void println(int)>($stack14);

      $stack17 = <java.lang.System: java.io.PrintStream out>;
      $stack16 = 1123 + 1;
      virtualinvoke $stack17.<java.io.PrintStream: 
        void println(int)>($stack16);

      $stack19 = <java.lang.System: java.io.PrintStream out>;
      $stack18 = 123456 + 1;
      virtualinvoke $stack19.<java.io.PrintStream: 
        void println(int)>($stack18);

      $stack21 = <java.lang.System: java.io.PrintStream out>;
      $stack20 = 10L + 1L;
      virtualinvoke $stack21.<java.io.PrintStream: 
        void println(long)>($stack20);

      $stack23 = <java.lang.System: java.io.PrintStream out>;
      $stack22 = 10.1 + 1.0;
      virtualinvoke $stack23.<java.io.PrintStream: 
        void println(double)>($stack22);

      $stack25 = <java.lang.System: java.io.PrintStream out>;
      $stack24 = 10.1F + 1.0F;
      virtualinvoke $stack25.<java.io.PrintStream: 
        void println(float)>($stack24);

      return;
  }
}
/*
  The JimpleLocal $stack12, $stack14, $stack16, $stack18 are of IntType. 
  Similarly, $stack20 is of LongType, $stack22 is of DoubleType and so on.
*/

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package target.exercise1;

public class DemoClass {
  public void display(){
    boolean varBoolean = true;
    byte varByte = 127;
    char varChar = 'a';
    short varShort = 1123;
    int varInt = 123456;
    long varLong = 10L;
    double varDouble = 10.10;
    float varFloat = 10.10f;

    System.out.println(!varBoolean);
    System.out.println(varByte-1);
    System.out.println(varChar+1);
    System.out.println(varShort+1);
    System.out.println(varInt+1);
    System.out.println(varLong+1);
    System.out.println(varDouble+1);
    System.out.println(varFloat+1);

  }
}

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// class version 52.0 (52)
// access flags 0x21
public class target/exercise1/DemoClass {

// compiled from: DemoClass.java

// access flags 0x1
public <init>()V
  L0
    LINENUMBER 3 L0
    ALOAD 0
    INVOKESPECIAL java/lang/Object.<init> ()V
    RETURN
  L1
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L1 0
    MAXSTACK = 1
    MAXLOCALS = 1

// access flags 0x1
public display()V
  L0
    LINENUMBER 5 L0
    ICONST_1
    ISTORE 1
  L1
    LINENUMBER 6 L1
    BIPUSH 127
    ISTORE 2
  L2
    LINENUMBER 7 L2
    BIPUSH 97
    ISTORE 3
  L3
    LINENUMBER 8 L3
    SIPUSH 1123
    ISTORE 4
  L4
    LINENUMBER 9 L4
    LDC 123456
    ISTORE 5
  L5
    LINENUMBER 10 L5
    LDC 10
    LSTORE 6
  L6
    LINENUMBER 11 L6
    LDC 10.1
    DSTORE 8
  L7
    LINENUMBER 12 L7
    LDC 10.1
    FSTORE 10
  L8
    LINENUMBER 14 L8
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    ILOAD 1
    IFNE L9
    ICONST_1
    GOTO L10
  L9
    FRAME FULL [target/exercise1/DemoClass I I I I I J D F] 
      [java/io/PrintStream]
    ICONST_0
  L10
    FRAME FULL [target/exercise1/DemoClass I I I I I J D F] 
      [java/io/PrintStream I]
    INVOKEVIRTUAL java/io/PrintStream.println (Z)V
  L11
    LINENUMBER 15 L11
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    ILOAD 2
    ICONST_1
    ISUB
    INVOKEVIRTUAL java/io/PrintStream.println (I)V
  L12
    LINENUMBER 16 L12
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    ILOAD 3
    ICONST_1
    IADD
    INVOKEVIRTUAL java/io/PrintStream.println (I)V
  L13
    LINENUMBER 17 L13
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    ILOAD 4
    ICONST_1
    IADD
    INVOKEVIRTUAL java/io/PrintStream.println (I)V
  L14
    LINENUMBER 18 L14
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    ILOAD 5
    ICONST_1
    IADD
    INVOKEVIRTUAL java/io/PrintStream.println (I)V
  L15
    LINENUMBER 19 L15
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    LLOAD 6
    LCONST_1
    LADD
    INVOKEVIRTUAL java/io/PrintStream.println (J)V
  L16
    LINENUMBER 20 L16
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    DLOAD 8
    DCONST_1
    DADD
    INVOKEVIRTUAL java/io/PrintStream.println (D)V
  L17
    LINENUMBER 21 L17
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    FLOAD 10
    FCONST_1
    FADD
    INVOKEVIRTUAL java/io/PrintStream.println (F)V
  L18
    LINENUMBER 23 L18
    RETURN
  L19
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L19 0
    LOCALVARIABLE varBoolean Z L1 L19 1
    LOCALVARIABLE varByte B L2 L19 2
    LOCALVARIABLE varChar C L3 L19 3
    LOCALVARIABLE varShort S L4 L19 4
    LOCALVARIABLE varInt I L5 L19 5
    LOCALVARIABLE varLong J L6 L19 6
    LOCALVARIABLE varDouble D L7 L19 8
    LOCALVARIABLE varFloat F L8 L19 10
    MAXSTACK = 5
    MAXLOCALS = 11
}

ReferenceType

ClassType, ArrayType NullType 

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public class target.exercise1.DemoClass extends java.lang.Object
{
public void <init>()
  {
  target.exercise1.DemoClass this;
  this := @this: target.exercise1.DemoClass;
  specialinvoke this.<java.lang.Object: void <init>()>();
  return;
  }

  public target.exercise1.DemoClass getObject(target.exercise1.DemoClass)
  {
  target.exercise1.DemoClass obj, this;
  this := @this: target.exercise1.DemoClass;
  obj := @parameter0: target.exercise1.DemoClass;
  return obj;
  }

  public void compute(boolean)
  {
  int[] b;
  java.io.PrintStream $stack5, $stack6;
  boolean check;
  target.exercise1.DemoClass this;
  int i;
  null_type $r0;
  java.lang.NullPointerException soot0;
  this := @this: target.exercise1.DemoClass;
  check := @parameter0: boolean;
  b = newarray (int)[5];
  i = 0;

  label1:
    if i >= 5 goto label3;
      if check == 0 goto label2;
      $r0 = (null_type) i;
      soot0 = new java.lang.NullPointerException;
      specialinvoke soot0.<java.lang.NullPointerException: 
        void <init>(java.lang.String)>
          ("This statement would have triggered an Exception: a[i#1] = $r0");
      throw soot0;

  label2:
  b[i] = i;
      i = i + 1;
      goto label1;

  label3:
      $stack5 = <java.lang.System: java.io.PrintStream out>;
      virtualinvoke $stack5.<java.io.PrintStream: 
        void println(java.lang.Object)>(b);
      $stack6 = <java.lang.System: java.io.PrintStream out>;
      virtualinvoke $stack6.<java.io.PrintStream: 
        void println(java.lang.Object)>(null);
      return;
  }
}
/*
  The JimpleLocal b is of ArrayType,
    and JimpleLocal $r0 is of NullType.
*/

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package target.exercise1;

public class DemoClass {

  public DemoClass getObject(DemoClass obj){
    return obj;
  }

  public void compute(boolean check){
    int a[] = null;
    int b[] = new int[5];
    for (int i = 0; i < 5; i++) {
      if(check){
        a[i] = i;
      }
        b[i] = i;
    }
    System.out.println(b);
    System.out.println(a);
  }
}

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// class version 52.0 (52)
// access flags 0x21
public class target/exercise1/DemoClass {

// compiled from: DemoClass.java

// access flags 0x1
public <init>()V
  L0
    LINENUMBER 3 L0
    ALOAD 0
    INVOKESPECIAL java/lang/Object.<init> ()V
    RETURN
  L1
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L1 0
    MAXSTACK = 1
    MAXLOCALS = 1

// access flags 0x1
public getObject(Ltarget/exercise1/DemoClass;)Ltarget/exercise1/DemoClass;
  L0
    LINENUMBER 6 L0
    ALOAD 1
    ARETURN
  L1
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L1 0
    LOCALVARIABLE obj Ltarget/exercise1/DemoClass; L0 L1 1
    MAXSTACK = 1
    MAXLOCALS = 2

// access flags 0x1
public compute(Z)V
  L0
    LINENUMBER 10 L0
    ACONST_NULL
    ASTORE 2
  L1
    LINENUMBER 11 L1
    ICONST_5
    NEWARRAY T_INT
    ASTORE 3
  L2
    LINENUMBER 12 L2
    ICONST_0
    ISTORE 4
  L3
    FRAME APPEND [[I [I I]
    ILOAD 4
    ICONST_5
    IF_ICMPGE L4
  L5
    LINENUMBER 13 L5
    ILOAD 1
    IFEQ L6
  L7
    LINENUMBER 14 L7
    ALOAD 2
    ILOAD 4
    ILOAD 4
    IASTORE
  L6
    LINENUMBER 16 L6
    FRAME SAME
    ALOAD 3
    ILOAD 4
    ILOAD 4
    IASTORE
  L8
    LINENUMBER 12 L8
    IINC 4 1
    GOTO L3
  L4
    LINENUMBER 18 L4
    FRAME CHOP 1
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    ALOAD 3
    INVOKEVIRTUAL java/io/PrintStream.println (Ljava/lang/Object;)V
  L9
    LINENUMBER 19 L9
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    ALOAD 2
    INVOKEVIRTUAL java/io/PrintStream.println (Ljava/lang/Object;)V
  L10
    LINENUMBER 20 L10
    RETURN
  L11
    LOCALVARIABLE i I L3 L4 4
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L11 0
    LOCALVARIABLE check Z L0 L11 1
    LOCALVARIABLE a [I L1 L11 2
    LOCALVARIABLE b [I L2 L11 3
    MAXSTACK = 3
    MAXLOCALS = 5
}

Local

1
$i0
A Local is a variable and its scope is inside its method i.e. no referencing from outside a method. Values can be assigned to Locals via JIdentityStmt or JAssignStmt. 

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public class target.exercise1.DemoClass extends java.lang.Object
{
  public void <init>()
  {
    target.exercise1.DemoClass this;
    this := @this: target.exercise1.DemoClass;
    specialinvoke this.<java.lang.Object: void <init>()>();
    return;
  }

  public void compute()
  {
    java.io.PrintStream $stack2, $stack3;
    target.exercise1.DemoClass this;
    int local#2;

    this := @this: target.exercise1.DemoClass;
    $stack2 = <java.lang.System: java.io.PrintStream out>;
    virtualinvoke $stack2.<java.io.PrintStream: void println(int)>(1);

    local#2 = this.<target.exercise1.DemoClass: int global>;
    $stack3 = <java.lang.System: java.io.PrintStream out>;
    virtualinvoke $stack3.<java.io.PrintStream: void println(int)>(local#2);
    return;
  }
}
/*
  $stack2, this, $stack3, local#2 are all JimpleLocal.

  "this := @this: target.exercise1.DemoClass" is JIdentityStmt

  "$stack2 = <java.lang.System: java.io.PrintStream out>", 
    "local#2 = this.<target.exercise1.DemoClass: int global>", 
      "$stack3 = <java.lang.System: java.io.PrintStream out>" 
        are JAssignStmt

*/  

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package target.exercise1;

public class DemoClass {

  private int global;

  public void compute(){
    int local;
    local = 1;
    System.out.println(local);
    local = this.global;
    System.out.println(local);
  }
}

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// class version 52.0 (52)
// access flags 0x21
public class target/exercise1/DemoClass {

// compiled from: DemoClass.java

// access flags 0x2
private I global

// access flags 0x1
public <init>()V
  L0
    LINENUMBER 3 L0
    ALOAD 0
    INVOKESPECIAL java/lang/Object.<init> ()V
    RETURN
  L1
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L1 0
    MAXSTACK = 1
    MAXLOCALS = 1

// access flags 0x1
public compute()V
  L0
    LINENUMBER 9 L0
    ICONST_1
    ISTORE 1
  L1
    LINENUMBER 10 L1
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    ILOAD 1
    INVOKEVIRTUAL java/io/PrintStream.println (I)V
  L2
    LINENUMBER 11 L2
    ALOAD 0
    GETFIELD target/exercise1/DemoClass.global : I
    ISTORE 1
  L3
    LINENUMBER 12 L3
    GETSTATIC java/lang/System.out : Ljava/io/PrintStream;
    ILOAD 1
    INVOKEVIRTUAL java/io/PrintStream.println (I)V
  L4
    LINENUMBER 14 L4
    RETURN
  L5
    LOCALVARIABLE this Ltarget/exercise1/DemoClass; L0 L5 0
    LOCALVARIABLE local I L1 L5 1
    MAXSTACK = 2
    MAXLOCALS = 2
}

Constant

represents a value itself. don't confuse it with a variable/Local which has a immutable (i.e. final) attribute.

There exists a constant entity for every Type - that way all value types can have a representation.

Expr

An expression is a language construct that returns a value. E.g. a binary operation such as addition.

Ref

JArrayRef

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$arr[1]
referencing a position inside an array.

JFieldRef (JStaticFieldRef & JInstanceFieldRef)

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<SomePackage.ExampleClass: fieldname>
// or
$r1.<SomePackage.ExampleClass: fieldname>
referencing a Field via its FieldSignature and if necessary (i.e. with JInstanceFieldRef) the corresponding Local instance that points to the object instance.

IdentityRef

The IdentityRef makes those implicit special value assignments explicit.

JThisRef

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@this: package.fruit.Banana
represents the this pointer of the current class.

JCaughtExceptionRef

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@caughtexception
represents the value of the thrown exception (caught by this exceptionhandler).

JParameterRef

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2
$i0 := @parameter0
$i1 := @parameter1
represents a parameter of a method, identified by its index.