String類型作爲鎖的弊端

package com.freeflying.thread.sync;
/**
 * 使用String類型作爲鎖
 * @ClassName: ConstantPoolString  
 * @Description:
 * @author freeflying
 * @date 2018年7月5日
 */
public class ConstantPoolString {
	public static void main(String[] args) {
		ConstantPoolStringEx constantPoolStringEx=new ConstantPoolStringEx();
		ConstantPoolStringA constantPoolStringA=new ConstantPoolStringA(constantPoolStringEx);
		constantPoolStringA.setName("A");
		constantPoolStringA.start();
		ConstantPoolStringB constantPoolStringB=new ConstantPoolStringB(constantPoolStringEx);
		constantPoolStringB.setName("B");
		constantPoolStringB.start();
	}
}
class ConstantPoolStringEx{
	public static void print(String string) {
		try {
			synchronized (string) {
				while (true) {
					System.out.println(Thread.currentThread().getName());
					Thread.sleep(1000);
				}
			}
		} catch (Exception e) {
			// TODO: handle exception
		}
	}
}
class ConstantPoolStringA extends Thread{
	private ConstantPoolStringEx constantPoolStringEx;
	public ConstantPoolStringA(ConstantPoolStringEx constantPoolStringEx) {
		this.constantPoolStringEx=constantPoolStringEx;
	}
	@Override
	public void run() {
		constantPoolStringEx.print("AA");
	}
}
class ConstantPoolStringB extends Thread{
	private ConstantPoolStringEx constantPoolStringEx;
	public ConstantPoolStringB(ConstantPoolStringEx constantPoolStringEx) {
		this.constantPoolStringEx=constantPoolStringEx;
	}
	@Override
	public void run() {
		constantPoolStringEx.print("AA");
	}
}

結果

A
A
A
A
A
A
A
A
A
A
A
A

結論：

因爲在JVM中具有String常量池(如果兩個String具有相同的值，那麼他們的地址是相同的，都保存在這個常量池中)。當以String作爲鎖的時候，如果值相同則，那麼線程持有相同的鎖。這樣就造成了另外一個線程不能執行