@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();

    }