三、singleton(单例化)一个对象的几种方法

@Test
    public void test13() {
        A215 a=A215.a;
        A215 b=A215.a;
        System.out.println(a==b);//true
    }

class A215{
    public static final A215 a=new A215();
    private A215(){}
}

@Test
    public void test20() {
        A211 a1=A211.getA211();
        A211 a2=A211.getA211();
        System.out.println(a1==a2);//true
    }

class A211{
    private static final A211 a=new A211();
    public static A211 getA211(){
        return a;
    }
}

@Test
    public void test12() {
        A216 a217 = A216.A217;
        A216 a218 = A216.A217;
        System.out.println(a217==a218);//true
    }
}
enum A216{
    A217;
    private A217 a=null;
    private A216(){
        a=new A217();
        a.name="wangyang";
    }
    public A217 getA217(){
        return a;
    }
    
}
class A217{
    public String name;
    public void hello(){
        System.out.println("hello "+name);
    }
}