ClassGen cg = new ClassGen("Test1","java.lang.Object",ACC_PUBLIC|ACC_SUPER);

FieldGen fg = cg.addField("message",Type.STRING,ACC_PRIVATE|ACC_STATIC);
fg.setConstantValue("Hello, World");

MethodGen mg = cg.addMethod("main",Type.VOID,new Type[]{Type.arrayType(Type.STRING)},ACC_STATIC|ACC_PUBLIC);
mg.add(LDC,10);
mg.add(ISTORE_0);

int top = mg.size();
mg.add(GETSTATIC,new FieldRef("java.lang.System","out",new Type.Object("java.io.PrintStream")));
mg.add(NEW,Type.STRINGBUFFER);
mg.add(DUP);
mg.add(INVOKESPECIAL,new MethodRef(Type.STRINGBUFFER,"<init>",Type.VOID,Type.NO_ARGS));
mg.add(GETSTATIC,new FieldRef("Test1","message",Type.STRING));
mg.add(INVOKEVIRTUAL,new MethodRef(Type.STRINGBUFFER,"append",Type.STRINGBUFFER,new Type[]{Type.STRING}));
mg.add(LDC," - ");
mg.add(INVOKEVIRTUAL,new MethodRef(Type.STRINGBUFFER,"append",Type.STRINGBUFFER,new Type[]{Type.STRING}));
mg.add(ILOAD_0);
mg.add(INVOKEVIRTUAL,new MethodRef(Type.STRINGBUFFER,"append",Type.STRINGBUFFER,new Type[]{Type.INT}));

mg.add(ILOAD_0);
mg.add(ICONST_1);
mg.add(IAND);
int b1 = mg.add(IFNE);
mg.add(LDC,'!');
mg.add(INVOKEVIRTUAL,new MethodRef(Type.STRINGBUFFER,"append",Type.STRINGBUFFER,new Type[]{Type.CHAR}));
mg.setArg(b1,mg.size());

mg.add(INVOKEVIRTUAL,new MethodRef(Type.STRINGBUFFER,"toString",Type.STRING,Type.NO_ARGS));
mg.add(INVOKEVIRTUAL,new MethodRef("java.io.PrintStream","println",Type.VOID,new Type[]{Type.STRING}));

mg.add(IINC,new MethodGen.Pair(0,-1));

mg.add(ILOAD_0);
mg.add(IFGT,top);

mg.add(RETURN);

cg.dump("Test1.class");

public class Test1 extends java.lang.Object{
private static java.lang.String message;

public static void main(java.lang.String[]);
   throws 
  Code:
   0:   bipush  10
   2:   istore_0
   3:   getstatic       #10; //Field java/lang/System.out:Ljava/io/PrintStream;
   6:   new     #12; //class StringBuffer
   9:   dup
   10:  invokespecial   #16; //Method java/lang/StringBuffer."<init>":()V
   13:  getstatic       #20; //Field message:Ljava/lang/String;
   16:  invokevirtual   #24; //Method java/lang/StringBuffer.append:(Ljava/lang/String;)Ljava/lang/StringBuffer;
   19:  ldc     #26; //String  - 
   21:  invokevirtual   #24; //Method java/lang/StringBuffer.append:(Ljava/lang/String;)Ljava/lang/StringBuffer;
   24:  iload_0
   25:  invokevirtual   #29; //Method java/lang/StringBuffer.append:(I)Ljava/lang/StringBuffer;
   28:  iload_0
   29:  iconst_1
   30:  iand
   31:  ifne    39
   34:  bipush  33
   36:  invokevirtual   #32; //Method java/lang/StringBuffer.append:(C)Ljava/lang/StringBuffer;
   39:  invokevirtual   #36; //Method java/lang/StringBuffer.toString:()Ljava/lang/String;
   42:  invokevirtual   #42; //Method java/io/PrintStream.println:(Ljava/lang/String;)V
   45:  iinc    0, -1
   48:  iload_0
   49:  ifgt    3
   52:  return

}

Hello, World - 10!
Hello, World - 9
Hello, World - 8!
Hello, World - 7
Hello, World - 6!
Hello, World - 5
Hello, World - 4!
Hello, World - 3
Hello, World - 2!
Hello, World - 1