Optional 类

    @Test
    public void test2(){
        Girl girl = new Girl();
//        girl = null;
        //ofNullable(T t)：t可以为null
        Optional<Girl> optionalGirl = Optional.ofNullable(girl);
        System.out.println(optionalGirl);
        //orElse(T t1):如果单前的Optional内部封装的t是非空的，则返回内部的t.
        //如果内部的t是空的，则返回orElse()方法中的参数t1.
        Girl girl1 = optionalGirl.orElse(new Girl("赵丽颖"));
        System.out.println(girl1);

    }

 @Test
    public void test4(){
        Boy boy = new Boy();
        boy = null;
        String girlName = getGirlName1(boy);
        System.out.println(girlName);

    }

    //使用Optional类的getGirlName():
    public String getGirlName2(Boy boy){

        Optional<Boy> boyOptional = Optional.ofNullable(boy);
        //此时的boy1一定非空
        Boy boy1 = boyOptional.orElse(new Boy(new Girl("迪丽热巴")));

        Girl girl = boy1.getGirl();

        Optional<Girl> girlOptional = Optional.ofNullable(girl);
        //girl1一定非空
        Girl girl1 = girlOptional.orElse(new Girl("古力娜扎"));

        return girl1.getName();
    }