Day12 单例模式

一个类在一个系统中，从头到尾只有一个对象

范例：懒汉式

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

public class TextSingleton {
    public static void main(String[] args) {
        Singleton s1=Singleton.getInstance();
        Singleton s2=Singleton.getInstance();
        System.out.println(s1);
        System.out.println(s2);
        System.out.println(s1==s2);
    }

范例：饿汉式

public class Singleton {
    private static Singleton s;
    private Singleton(){}
    static {
        s=new Singleton();
    }
    public static Singleton getInstance(){
        return s;
    }
}