HelloDefineClass.java

package com.govuln.bytes;

import org.apache.commons.codec.binary.Base64;

import java.lang.reflect.Method;

public class HelloDefineClass {
    public static void main(String[] args) throws Exception {
        Method defineClass = ClassLoader.class.getDeclaredMethod("defineClass", String.class, byte[].class, int.class, int.class);
        defineClass.setAccessible(true);

        // source: bytecodes/Hello.java
        byte[] code = Base64.decodeBase64("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");
        Class hello = (Class)defineClass.invoke(ClassLoader.getSystemClassLoader(), "Hello", code, 0, code.length);
        hello.newInstance();
    }
}