Guide: How to use Java decompilation tools

Guidelines for using Java decompilation tools

Introduction:
Java is a widely used programming language, and the written code cannot be read directly after deployment , which caused certain troubles. To solve this problem, we can use decompilation tools to reverse-transform the deployed Java code so that we can view, analyze, and modify it. This article will introduce how to use several commonly used Java decompilation tools and provide specific code examples.

1. JD-GUI
JD-GUI is a free Java decompilation tool that can convert compiled Java code into highly readable Java source code. It is very easy to use, just download and install it, and then open the Java class file that needs to be decompiled.

Sample code:

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, world!");
    }
}

Use JD-GUI to open the compiled HelloWorld.class file, and you can see the decompiled Java source code:

public class HelloWorld {
     public static void main(String[] paramArrayOfString) {
          System.out.println("Hello, world!");
     }
}

2. Bytecode Viewer
Bytecode Viewer is another commonly used Java decompilation tool. It supports decompilation of Java bytecode files and can convert them into more readable Java source code. Similar to JD-GUI, using Bytecode Viewer is also very simple. Just download and install it, and then open the bytecode file that needs to be decompiled.

Sample code:

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, world!");
    }
}

Use Bytecode Viewer to open the compiled HelloWorld.class file, and you can see the decompiled Java source code:

public class HelloWorld {
     public static void main(String[] paramArrayOfString) {
          System.out.println("Hello, world!");
     }
}

3. Procyon
Procyon is a powerful open source Java decompilation tool. It supports decompiling bytecode files of Java 5 and above, and the output Java source code is of high quality. Using the Procyon decompilation tool requires downloading and installing its runtime environment.

Sample code:

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, world!");
    }
}

Use Procyon’s command line tool to convert the compiled HelloWorld.class file into Java source code:

java -jar procyon-decompiler.jar HelloWorld.class

The output result is:

public class HelloWorld {
    public static void main(final String[] array) {
        System.out.println("Hello, world!");
    }
}

4. Cfr
Cfr is another commonly used open source Java decompilation tool. It supports decompilation of multiple versions of bytecode files, and the output Java source code has good readability. Using the Cfr decompilation tool requires downloading and installing its runtime environment.

Sample code:

public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello, world!");
    }
}

Use Cfr’s command line tool to convert the compiled HelloWorld.class file into Java source code:

java -jar cfr.jar HelloWorld.class

The output result is:

public class HelloWorld {
    public static void main(final String[] array) {
        System.out.println("Hello, world!");
    }
}

Summary:
Java decompilation tool is one of the must-have tools for developers. It can easily convert compiled Java code into more readable Java source code, which facilitates our code analysis. and modifications. This article introduces several commonly used Java decompilation tools and provides specific code examples. The above are just the basic usage methods of the tool. Readers can further learn and master more advanced usage skills according to their own needs. Hope this article is helpful to readers.

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