https://github.com/cglib/cglib/cglib: cglib is a powerful, high performance and quality Code Generation Library, It is used to extend JAVA classes and implements interfaces at runtime. 
/*
 * Copyright 2003 The Apache Software Foundation
 *
 *  Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package net.sf.cglib.core;

import org.objectweb.asm.Label;

public class Block
{
    private CodeEmitter e;
    private Label start;
    private Label end;

    public Block(CodeEmitter e) {
        this.e = e;
        start = e.mark();
    }

    public CodeEmitter getCodeEmitter() {
        return e;
    }

    public void end() {
        if (end != null) {
            throw new IllegalStateException("end of label already set");
        }
        end = e.mark();
    }
    
    public Label getStart() {
        return start;
    }

    public Label getEnd() {
        return end;
    }
}