http://www.javassist.org/: Javassist (JAVA programming ASSISTant) makes Java bytecode manipulation simple. It is a class library for editing bytecodes in Java. (Shigeru Chiba, www.javassist.org) 
/*
 * Javassist, a Java-bytecode translator toolkit.
 * Copyright (C) 1999- Shigeru Chiba. All Rights Reserved.
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License.  Alternatively, the contents of this file may be used under
 * the terms of the GNU Lesser General Public License Version 2.1 or later,
 * or the Apache License Version 2.0.
 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 */

package javassist.bytecode.stackmap;

import javassist.bytecode.StackMapTable;

public interface TypeTag {
    String TOP_TYPE = "*top*";
    TypeData.BasicType TOP = new TypeData.BasicType(TOP_TYPE, StackMapTable.TOP, ' ');
    TypeData.BasicType INTEGER = new TypeData.BasicType("int", StackMapTable.INTEGER, 'I');
    TypeData.BasicType FLOAT = new TypeData.BasicType("float", StackMapTable.FLOAT, 'F');
    TypeData.BasicType DOUBLE = new TypeData.BasicType("double", StackMapTable.DOUBLE, 'D');
    TypeData.BasicType LONG = new TypeData.BasicType("long", StackMapTable.LONG, 'J');

    // and NULL, THIS, OBJECT, UNINIT
}