二、单例模式（饿汉式）

类加载时创建。

public class SingleTon01 {
    public static void main(String[] args) {
        GirlFriend xh = GirlFriend.getInstance();
        GirlFriend xb = GirlFriend.getInstance();
        System.out.println(xh);
        System.out.println(xb);
        System.out.println(xh == xb);//true
    }
}

class GirlFriend {
    private String name;
    private static GirlFriend gf = new GirlFriend("小红");

    private GirlFriend(String name) {
        this.name = name;
    }

    public static GirlFriend getInstance() {
        return gf;
    }
 }

为了解决单例模式饿汉式创建构造方法没有使用，出现了懒汉式。

（一）懒汉式

使用时创建。

public class SingleTon02 {
    public static void main(String[] args) {
//        System.out.println(Cat.n1 );
        Cat instance=Cat.getInstance();
        System.out.println(instance);

        Cat instance2=Cat.getInstance();
        System.out.println(instance2);
    }
}

class Cat {
    private String name;
    public static int n1 = 999;
    private static Cat cat;

    private Cat(String name) {
        System.out.println("构造器调用");
        this.name = name;
    }

    public static Cat getInstance() {
        if (cat == null) {
            cat = new Cat("小可爱");
        }
        return cat;
    }
}