import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;

import org.objectweb.asm.*;

public class ASMBeispiel {
	public static ClassWriter beispiel1() throws IOException{
		
		ClassWriter cw = new ClassWriter( ClassWriter.COMPUTE_FRAMES | ClassWriter.COMPUTE_MAXS);
		
		cw.visit(Opcodes.V1_8,                  //Version 
				 Opcodes.ACC_PUBLIC,            //Access
				 "Bytecode",                    //Name
				 null,                          //Signatur
				 "java/lang/Object",            //Superklasse
				 null);                         //implemntierte Interfaces
		
		MethodVisitor constructor = 
				cw.visitMethod(Opcodes.ACC_PUBLIC,
				               "<init>",        //Name
				               "()V",           //Typ (Descriptor)
				               null,            //Signatur
				               null);           //Exceptions
		
		MethodVisitor method = 
				cw.visitMethod(Opcodes.ACC_PUBLIC, "m", "()V", null, null);
		
		//Konstruktor erstellen Start
		constructor.visitCode();               //Start-Initialisierung
		// aload_0
		constructor.visitVarInsn(Opcodes.ALOAD, 0);
		// invokespecial
		constructor.visitMethodInsn(Opcodes.INVOKESPECIAL,  //invoke-Befehl 
				                    "java/lang/Object",     //Owner-Klasse
				                    "<init>",               //Name
				                    "()V",                  //Typ (Descriptor)
				                    false);                 //is interface?
		// return
		constructor.visitInsn(Opcodes.RETURN); 
		
		constructor.visitMaxs(0, 0);          //maximale Anzahl des Stacks bzw. der lokalen Veriablen
		
		constructor.visitEnd();               //Ende-Initialisierung
		//Konstruktor erstellen Ende
		
		//Methode m erstellen Start 
		method.visitCode();
		// getstatic 
		method.visitFieldInsn(Opcodes.GETSTATIC,
		                      "java/lang/System", "out",
		                      "Ljava/io/PrintStream;");
		// ldc "Bytecode"
		method.visitLdcInsn("Bytecode");
		// invokevirtual 
		method.visitMethodInsn(Opcodes.INVOKEVIRTUAL,
		                       "java/io/PrintStream", "println", "(Ljava/lang/String;)V", false);
		// return
		method.visitInsn(Opcodes.RETURN); 
		
		method.visitMaxs(0, 0); 
		
		method.visitEnd();
		//Methode m erstellen Ende
		
		cw.visitEnd();
		
		return cw;
	}
	
	public static ClassWriter beispiel2() throws IOException{
		
		ClassWriter cw = new ClassWriter( ClassWriter.COMPUTE_FRAMES | ClassWriter.COMPUTE_MAXS);
		
		cw.visit(Opcodes.V1_8,                  //Version 
				 Opcodes.ACC_PUBLIC,            //Access
				 "Bytecode2",                    //Name
				 null,                          //Signatur
				 "java/lang/Object",            //Superklasse
				 null);                         //implemntierte Interfaces
		
		MethodVisitor constructor = 
				cw.visitMethod(Opcodes.ACC_PUBLIC,
				               "<init>",        //Name
				               "()V",           //Typ (Descriptor)
				               null,            //Signatur
				               null);           //Exceptions
		
		MethodVisitor method = 
				cw.visitMethod(Opcodes.ACC_PUBLIC, "m", "()V", null, null);
		
		//Konstruktor erstellen Start
		constructor.visitCode();               //Start-Initialisierung
		// aload_0
		constructor.visitVarInsn(Opcodes.ALOAD, 0);
		// invokespecial
		constructor.visitMethodInsn(Opcodes.INVOKESPECIAL,  //invoke-Befehl 
				                    "java/lang/Object",     //Owner-Klasse
				                    "<init>",               //Name
				                    "()V",                  //Typ (Descriptor)
				                    false);                 //is interface?
		// return
		constructor.visitInsn(Opcodes.RETURN); 
		
		constructor.visitMaxs(0, 0);          //maximale Anzahl des Stacks bzw. der lokalen Veriablen
		
		constructor.visitEnd();               //Ende-Initialisierung
		//Konstruktor erstellen Ende
		
		//Methode m erstellen Start 
		Label start = new Label(); 
		Label loop = new Label(); 
		Label end = new Label();
		
		method.visitLabel(start); 
		method.visitInsn(Opcodes.ICONST_0); 
		method.visitVarInsn(Opcodes.ISTORE, 1);
		
		method.visitLabel(loop);
		method.visitVarInsn(Opcodes.ILOAD, 1); 
		method.visitInsn(Opcodes.ICONST_5); 
		method.visitJumpInsn(Opcodes.IF_ICMPGE, end);
		
		method.visitFieldInsn(Opcodes.GETSTATIC, "java/lang/System", "out", "Ljava/io/PrintStream;");
		method.visitLdcInsn("Bytecode");
		method.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "java/io/PrintStream", "println",
		                       "(Ljava/lang/String;)V", false);
		
		method.visitIincInsn(1, 1); 
		method.visitJumpInsn(Opcodes.GOTO, loop);
		
		method.visitLabel(end);
		method.visitInsn(Opcodes.RETURN);
		
		method.visitMaxs(0, 0); 
		method.visitEnd();
		//Methode m erstellen Ende

		cw.visitEnd();
		
		return cw;
	}
		
     static void writeClassfile(ClassWriter cw) throws IOException{
    	byte[] bytes = cw.toByteArray();
    	String className = new ClassReader(bytes).getClassName();
		File outputFile = new File("./", className + ".class");
		FileOutputStream output = new FileOutputStream(outputFile);
		output.write(bytes);
		output.close();
	}
	
	
	public static void main(String args[]) throws IOException{
		writeClassfile(beispiel1());
		writeClassfile(beispiel2());
	}
}