1、饿汉式
public class SingleObject{
//创建SingleObject 的一个对象
private static SingleObject instance = new SingleObject();
private SingleObject(){}
public static SingleObject getInstance(){
return instance;
}
}
2、懒汉式，线程不安全
public class SingleObject{
private static SingleObject instace= null;
private SingleObject(){}
public static SingleObject getInstance(){
if(instance == null){
instance = new SingleObject();
}
return instance;
}
}
3、懒汉式、线程安全
public class SingleObject{
private static SingleObjct instance;
private SingleObject(){}
public static synchronized SingleObject getInstance(){
if(instance == null){
instance == new SingleObject()
}
return instance;
}
}
4、懒汉式双检锁/双重校验锁（DCL double-checked locking）、线程安全
public class SingleObject{
private static volatile SingleObject instance;
private SingleObject(){}
public static SingleObject getInstance(){
synchronize(SingleObject.class){
if(instance == null){
instance= new SingleObject();
}
return instance;
}
}
}
5、登记式/静态内部类
public class SingleObject{
private static class SingletonHolder {
private static final Singleton INSTANCE = new Singleton();
}
private SingleObject(){}
public static final SingleObject getInstance(){
return SingletonHolder.INSTANCE ;
}
}
}
6、枚举实现单例
publicclass EnumSingleton{
private EnumSingleton(){}
public static EnumSingleton getInstance(){
return Singleton.INSTANCE.getInstance();
}
private static enum Singleton{
INSTANCE;
private EnumSingleton singleton;
//JVM会保证此方法绝对只调用一次
private Singleton(){
singleton =new EnumSingleton();
}
public EnumSingleton getInstance(){
return singleton;
}
}
}
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