java单例模式的4种例子

饿汉式（线程不安全）java单例：
public class Hungry {

private static Hungry in= new Hungry();

private Hungry() {}

public static Hungry getIn() {
	return instance;
}

}
懒汉式（线程不安全）java单例：
public class Idler {

private static Idler =null;

private Hungry() {}

public static Idler getIdler () {
	if(instance==null) {
		instance=new S1();
	}
	return instance;
}

}
双重检查（线程安全）java实例：
public class Singleton {

private static volatile Singleton singleton;

private Singleton() {}

public static Singleton getInstance() {
    if (singleton == null) {
        synchronized (Singleton.class) {
            if (singleton == null) {
                singleton = new Singleton();
            }
        }
    }
    return singleton;
}

}
枚举java单例（线程安全）：
enum Color{
RED,GREEN,BLUE;
}
public class Hello {
public static void main(String[] args){
Color color=Color.RED;
int counter=10;
while (counter–>0){
switch (color){
case RED:
System.out.println(“Red”);
color=Color.BLUE;
break;
case BLUE:
System.out.println(“Blue”);
color=Color.GREEN;
break;
case GREEN:
System.out.println(“Green”);
color=Color.RED;
break;
}
}
}
}