import org.objectweb.asm.*; import org.objectweb.asm.tree.*; public class ASMTreeExample { public static void main(String[] args) { ClassReader cr = new ClassReader("ExampleClass"); ClassNode cn = new ClassNode(); cr.accept(cn, 0); for (MethodNode mn : cn.methods) { InsnList instructions = mn.instructions; instructions.clear(); instructions.add(new FieldInsnNode(Opcodes.GETSTATIC, "java/lang/System", "out", "Ljava/io/PrintStream;")); instructions.add(new LdcInsnNode("Hello, ASM Tree!")); instructions.add(new MethodInsnNode(Opcodes.INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V")); instructions.add(new InsnNode(Opcodes.RETURN)); } cn.accept(cw); byte[] modifiedBytes = cw.toByteArray(); // ... // ... } }