饿汉模式：
/**
* 单例-饿汉模式(即静态创建)
* 优点:线程安全,实现简单
* 缺点:SingleInstance 在类加载的时候就实例化了,即便不用。(如果不用的话会造成内存浪费)
* @author Rambo(浩祥)
* @create 2017-09-21
**/
public final class SingleInstance1 {
private static SingleInstance1 singleInstance = new SingleInstance1();
private SingleInstance1(){}
public static SingleInstance1 getSingleInstance(){
return singleInstance;
}
}
懒汉模式1
/**
* 单例--懒汉模式1(即用到的时候再去创建)
* 优点:不用场景下,比懒汉模式节省内存
* 缺点:非线程安全,耗时比懒汉模式长
* @author Rambo(浩祥)
* @create 2017-08-25
**/
public final class SingleInstance2 {
private static SingleInstance2 singleInstance = null;
private SingleInstance2(){
}
public static SingleInstance2 getSingleInstance(){
try {
if (singleInstance == null){
// 休眠50ms构造线程非安全的场景
Thread.sleep(50);
singleInstance = new SingleInstance2();
}
} catch (InterruptedException e) {
e.printStackTrace();
}
return singleInstance;
}
}
懒汉模式2
/**
* 单例-懒汉模式2
* 优点:较懒汉模式1比线程安全
* 缺点:较懒汉模式1耗时,因为要进行线程同步
* @author Rambo(浩祥)
* @create 2017-09-21
**/
public class SingleInstance3 {
private static SingleInstance3 singleInstance = null;
private SingleInstance3(){
}
public static synchronized SingleInstance3 getSingleInstance(){
try {
if (singleInstance == null){
// 休眠50ms构造线程非安全的场景
Thread.sleep(50);
singleInstance = new SingleInstance3();
}
} catch (InterruptedException e) {
e.printStackTrace();
}
return singleInstance;
}
}
懒汉模式3
/**
* 单例-懒汉模式3
* 优点-线程安全,比懒汉模式2节约用时
* @author Rambo(浩祥)
* @create 2017-09-21
**/
public class SingleInstance4 {
private static SingleInstance4 singleInstance = null;
private SingleInstance4(){
}
public static SingleInstance4 getSingleInstance(){
try {
if (singleInstance == null){
// 休眠50ms构造线程非安全的场景
Thread.sleep(50);
synchronized (SingleInstance4.class){
if (singleInstance == null){
singleInstance = new SingleInstance4();
}
}
}
} catch (InterruptedException e) {
e.printStackTrace();
}
return singleInstance;
}
}
懒汉模式4
/**
* 单例-懒汉模式4
*
* @author Rambo(浩祥)
* @create 2017-09-21
**/
public class SingleInstance5 {
private static class GetInstance{
private static SingleInstance5 singleInstance = new SingleInstance5();
}
private SingleInstance5(){
}
// 只有调用到该方法是GetInstance才会加载,singleInstance才会初始化
public static SingleInstance5 getSingleInstance(){
return GetInstance.singleInstance;
}
}
测试程序
验证不同单例模式的实例获取时间、内存占用、线程安全等
import com.rambo.memory.MemoryCounter;
/**
* @author Rambo(浩祥)
* @create 2017-03-09
**/
public class Practice {
// MemoryCounter是自己写的对象内存的计算类
private static MemoryCounter memoryCounter = new MemoryCounter();
public static void main(String[] args) {
Thread getInstanceThread = new Thread(new Runnable() {
@Override
public void run() {
getInstance();
}
});
getInstanceThread.start();
Thread getInstanceThread2 = new Thread(new Runnable() {
@Override
public void run() {
getInstance();
}
});
getInstanceThread2.start();
}
private static void getInstance() {
long startTime = System.currentTimeMillis();
// SingleInstance1 singleInstance1 = SingleInstance1.getSingleInstance();
// System.out.println(Thread.currentThread().getName() + ":singleInstance1获取对象消耗用时:" + (System.currentTimeMillis() - startTime));
// System.out.println(Thread.currentThread().getName() + ":singleInstance1对象hashCode:" + Integer.toString(singleInstance1.hashCode()));
// System.out.println(Thread.currentThread().getName() + ":singleInstance1线程对象大小:" + memoryCounter.estimate(singleInstance1));
// SingleInstance2 singleInstance2 = SingleInstance2.getSingleInstance();
// System.out.println(Thread.currentThread().getName() + ":singleInstance2获取对象消耗用时:" + (System.currentTimeMillis() - startTime));
// System.out.println(Thread.currentThread().getName() + ":singleInstance2对象hashCode:" + Integer.toString(singleInstance2.hashCode()));
// System.out.println(Thread.currentThread().getName() + ":singleInstance2线程对象大小:" + memoryCounter.estimate(singleInstance2));
//
// SingleInstance3 singleInstance3 = SingleInstance3.getSingleInstance();
// System.out.println(Thread.currentThread().getName() + ":singleInstance3获取对象消耗用时:" + (System.currentTimeMillis() - startTime));
// System.out.println(Thread.currentThread().getName() + ":singleInstance3对象hashCode:" + Integer.toString(singleInstance3.hashCode()));
// System.out.println(Thread.currentThread().getName() + ":singleInstance3线程对象大小:" + memoryCounter.estimate(singleInstance3));
//
// SingleInstance4 singleInstance4 = SingleInstance4.getSingleInstance();
// System.out.println(Thread.currentThread().getName() + ":singleInstance4获取对象消耗用时:" + (System.currentTimeMillis() - startTime));
// System.out.println(Thread.currentThread().getName() + ":singleInstance4对象hashCode:" + Integer.toString(singleInstance4.hashCode()));
// System.out.println(Thread.currentThread().getName() + ":singleInstance4线程对象大小:" + memoryCounter.estimate(singleInstance4));
//
SingleInstance5 singleInstance5 = SingleInstance5.getSingleInstance();
System.out.println(Thread.currentThread().getName() + ":singleInstance5获取对象消耗用时:" + (System.currentTimeMillis() - startTime));
System.out.println(Thread.currentThread().getName() + ":singleInstance5对象hashCode:" + Integer.toString(singleInstance5.hashCode()));
System.out.println(Thread.currentThread().getName() + ":singleInstance5线程对象大小:" + memoryCounter.estimate(singleInstance5));
}
}
运行结果如下：
饿汉
懒汉1，非线程安全
懒汉2
懒汉3
懒汉4
注：耗时大于50的是因为加了sleep（50）模拟线程非安全
注：实际应用建议应用懒汉4的方式
