Reverse Engineering for Beginners

CHAPTER 54. JAVA CHAPTER 54. JAVA

stack=2, locals=2, args_size=2

0: new #3 // class java/lang/StringBuilder

3: dup

4: invokespecial #4 // Method java/lang/StringBuilder."<init>":()V

7: aload_0

8: invokevirtual #5 // Method java/lang/StringBuilder.append:(Ljava/⤦

Çlang/String;)Ljava/lang/StringBuilder;

11: aload_1

12: invokevirtual #5 // Method java/lang/StringBuilder.append:(Ljava/⤦

Çlang/String;)Ljava/lang/StringBuilder;

15: invokevirtual #6 // Method java/lang/StringBuilder.toString:()⤦

ÇLjava/lang/String;

18: areturn

Another example:

public static void main(String[] args)

{

String s="Hello!";

int n=123;

System.out.println("s=" + s + " n=" + n);

}

And again, the strings are constructed using theStringBuilderclass and itsappendmethod, then the constructed string
is passed toprintln:

public static void main(java.lang.String[]);

flags: ACC_PUBLIC, ACC_STATIC

Code:

stack=3, locals=3, args_size=1

0: ldc #2 // String Hello!

2: astore_1

3: bipush 123

5: istore_2

6: getstatic #3 // Field java/lang/System.out:Ljava/io/⤦

ÇPrintStream;

9: new #4 // class java/lang/StringBuilder

12: dup

13: invokespecial #5 // Method java/lang/StringBuilder."<init>":()V

16: ldc #6 // String s=

18: invokevirtual #7 // Method java/lang/StringBuilder.append:(Ljava/⤦

Çlang/String;)Ljava/lang/StringBuilder;

21: aload_1

22: invokevirtual #7 // Method java/lang/StringBuilder.append:(Ljava/⤦

Çlang/String;)Ljava/lang/StringBuilder;

25: ldc #8 // String n=

27: invokevirtual #7 // Method java/lang/StringBuilder.append:(Ljava/⤦

Çlang/String;)Ljava/lang/StringBuilder;

30: iload_2

31: invokevirtual #9 // Method java/lang/StringBuilder.append:(I)Ljava⤦

Ç/lang/StringBuilder;

34: invokevirtual #10 // Method java/lang/StringBuilder.toString:()⤦

ÇLjava/lang/String;

37: invokevirtual #11 // Method java/io/PrintStream.println:(Ljava/lang⤦

Ç/String;)V

40: return

54.15Exceptions.

Let’s rework ourMonthexample (54.13.4 on page 605) a bit:

Listing 54.10: IncorrectMonthException.java

public class IncorrectMonthException extends Exception
{
private int index;

public IncorrectMonthException(int index)