解决多线程下单例模式中"懒汉模式"（延迟加载）的问题

获取单例对象的代码

public class MyObject {
private MyObject(){}
private static MyObject object;
public static MyObject getInstance() {
try {
if (object == null) {

object = new MyObject()；
}
} catch (InterruptedException e) {
e.printStackTrace();
}

return object;
}
}

当启动多个线程执行MyObject.getInstance()的时候，获取到的对象会有多个，解决办法：

在getInstance()方法上加synchronized关键字
public class MyObject {   		   private MyObject(){}
private static MyObject object;
synchronized public static MyObject getInstance() {
try {
if (object == null) {

object = new MyObject()；
}
} catch (InterruptedException e) {
e.printStackTrace();
}

return object;
}
}

这样整个方法会被上锁，效率低。

使用DCL双检查锁机制
public class MyObject {   		   private MyObject(){}
private static MyObject object;
public static MyObject getInstance() {
try {
if (object == null) {

synchronized(Myobject.class){

if(object==null){

object = new MyObject()；

}

}
}
} catch (InterruptedException e) {
e.printStackTrace();
}

return object;
}
}

使用静态内置类实现单例
			public class MyObject {
private MyObject(){}

private static class MyObjectHandler{
private static MyObject myObject = new MyObject();
}
public static MyObject getInstance() {

return MyObjectHandler.myObject;
}
}

该方法在序列化及序列化的时候前后得到的对象会发生变化，添加readResove()方法即可：

			public class MyObject implements Serializable {
private static final long serialVersionUID = 1L;
private MyObject(){}
private static class MyObjectHandler{
private static final MyObject myObject = new MyObject();
}
public static MyObject getInstance() {
return MyObjectHandler.myObject;
}
protected Object readResolve() throws ObjectStreamException{
System.out.println("调用了readResolve方法! ");
return MyObjectHandler.myObject;
}
}