Singleton_单例模式：

Singleton_单例模式：

常规实现：
public class Singleton{

private Singleton(){
}

private final static Singleton INSTANCE=new Singleton();

public static Singleton getInstance(){
return INSTANCE;
}

public static void main(String[] args){
for(int=0;i<100:i++){
new Thread(()->{
System.out.println(Singleton.getInstance().hashCode());
}).start();
}
}
}

内部类实现：
public class Singleton{

private Singleton(){
}

private static class SingletonHlder{
private final static Singleton INSTANCE=new Singleton();
}

public static Singleton getInstance(){
return SingletonHlder.INSTANCE;
}

public static void main(String[] args){
for(int=0;i<100:i++){
new Thread(()->{
System.out.println(Singleton.getInstance().hashCode());
}).start();
}
}
}

枚举类型实现：
public enum Singleton{
INSTANCE;

public static void main(String[] args){
for(int=0;i<100:i++){
new Thread(()->{
System.out.println(Singleton.INSTANCE.hashCode());
}).start();
}
}
}