用lock实现多线程下的单例(懒汉式) - 黑马程序员技术交流社区

package test;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
*
* @author fjl
*
*/
class Single{
private static Single s=null;
//构造方法私有化
private Single(){}
//创建一个锁对象，由于getInstance()是静态方法,则必须是静态成员该方法才能访问，
//并将锁声明成final类型，保持该对象不变且只有一个Lock对象
private static final Lock lock=new ReentrantLock();
//获得单例实例
public static Single getInstance(){
//如果为空
if(s==null){
//获取锁
lock.lock();
//如果该锁未被其他线程保持（可以查看API），即该锁是空闲的
if(lock.tryLock()){
if(s==null){
//实例化Single对象
s=new Single();
}
}
}
//返回
return s;
}
}
//多线程下测试
class Test1 implements Runnable{
@Override
public void run() {
// TODO Auto-generated method stub
while(true){
try {
Thread.sleep(100);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println(this+"-->"+Single.getInstance());
}
}
}
//多线程测试
class Test2 implements Runnable{
@Override
public void run() {
// TODO Auto-generated method stub
while(true){
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println(this+"-->"+Single.getInstance());
}
}
}
public class Demo01 {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
// Single s1=Single.getInstance();
// Single s2=Single.getInstance();
// System.out.println(s1==s2);
//多线程下测试
Thread one=new Thread(new Test1());
Thread one1=new Thread(new Test1());
Thread one2=new Thread(new Test1());
Thread two=new Thread(new Test2());
Thread two1=new Thread(new Test2());
Thread two2=new Thread(new Test2());
two.start();
two1.start();
two2.start();
one.start();
one1.start();
one2.start();
}
}

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