java单例模式实现的几种方式
单例模式好多书上都是这么写的：
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public class singleton1 {
private singleton1(){
}
private static singleton1 instance = null;
public static singleton1 getinstance(){
if(instance == null){
instance = new singleton1();
}
return instance;
}
}
但是实际开发中是不会这么写的，因为有一个严重的问题，多线程并发访问的时候，可能会产生多个实例！！
下面列举几个常用的方法：
1.使用synchronized 关键字
package singleton;
public class singleton1 {
private singleton1(){
}
private static singleton1 instance = null;
//多线程问题解法一，但是效率不高！因为每次调用都会加锁！
public static synchronized singleton1 getinstance(){
if(instance == null){
instance = new singleton1();
}
return instance;
}
public void print(){
system.out.println("thread_id:"+thread.currentthread().getid());
}
private static object object = new object();
//很巧妙的方法，只有在null的时候加锁，之后就不加啦
public static singleton1 getinstance2(){
if(instance == null){
synchronized (object){
instance = new singleton1();
}
}
return instance;
}
}
2.加锁
package singleton;
import java.util.concurrent.locks.reentrantlock;
public class singleton2 {
private singleton2(){
}
private static reentrantlock lock = new reentrantlock();
private static singleton2 instance = null;
public void print(){
system.out.println("thread_id:"+thread.currentthread().getid());
}
public static singleton2 getinstance2(){
if(instance == null){
lock.lock();
if(instance == null){ //注意这里还要判断下！！
instance = new singleton2();
}
lock.unlock();
}
return instance;
}
}
3.利用静态变量：
package singleton;
public class singleton3 {
public static void print(){
system.out.println("thread_id:"+thread.currentthread().getid());
}
public static nested getnested(){
return nested.instance;
}
//这个是单例创建的类
static class nested{
private nested(){
}
static nested instance = new nested();
}
}
以上就是常用的创建单例的模式：
test测试代码：
package singleton;
import singleton.singleton3.nested;
public class test2 {
public static void main(string[] args) {
// todo auto-generated method stub
nested singleton;
myrunnable mm = new myrunnable();
myrunnable m1 = new myrunnable();
myrunnable2 m2 = new myrunnable2();
new thread(m1).start();
new thread(m2).start();
if(m1.singleton == m2.singleton){ //是同一个
system.out.println("是同一个");
}else{
system.out.println("不是同一个");
}
}
}
class myrunnable implements runnable{
nested singleton;
@override
public void run() {
// todo auto-generated method stub
singleton = singleton3.getnested();
singleton3.print();
}
}
class myrunnable2 implements runnable{
nested singleton;
@override
public void run() {
// todo auto-generated method stub
singleton = singleton3.getnested();
singleton3.print();
}
}
输出：
是同一个
thread_id:11
thread_id:10
以上就是对java 单例模式的资料整理，后续继续补充相关资料，谢谢大家对本站的支持！
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