Java 基础(Optional类)

Optional提供很多有用的方法，这样我们就不用显式进行空值检测。

OptionalTest.java

package com.klvchen.java4;

import org.junit.Test;

import java.util.Optional;

public class OptionalTest {

    /*
    Optional.of(T t) : 创建一个 Optional 实例，t 必须非空;
    Optional.empty() : 创建一个空的 Optional 实例
    Optional.ofNullable(T t): t 可以为 null
     */

    @Test
    public void test1(){
        Girl girl = new Girl();
        girl = null;
        Optional optionalGirl = Optional.of(girl);
    }

    @Test
    public void test2(){
        Girl girl = new Girl();
        girl = null;
        //ofNullable(T t): t可以为null
        Optional optionalGirl = Optional.ofNullable(girl);
        System.out.println(optionalGirl);
        // orElse(T t1):如果当前的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);
    }

    public String getGirlName(Boy boy){
        return boy.getGirl().getName();

    }

    @Test
    public void test3(){
        Boy boy = new Boy();
        boy = null;
        String girlName = getGirlName(boy);
        System.out.println(girlName);
    }

    //优化以后的getGirlName():
    public String getGirlName1(Boy boy) {
        if (boy != null) {
            Girl girl = boy.getGirl();
            if (girl != null) {
                return girl.getName();
            }
        }
        return null;
    }

    @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 boyOptional = Optional.ofNullable(boy);

        Boy boy1 = boyOptional.orElse(new Boy(new Girl("迪丽热巴")));

        Girl girl = boy1.getGirl();

        Optional girlOptional = Optional.ofNullable(girl);
        Girl girl1 = girlOptional.orElse(new Girl("古力娜扎"));

        return girl1.getName();
    }

    @Test
    public void test5(){
        Boy boy = null;
        boy = new Boy();
        boy = new Boy(new Girl("苍老师"));
        String girlName = getGirlName2(boy);
        System.out.println(girlName);
    }
}

OptionalTest2.java

package com.klvchen.java;

import org.junit.Test;

import java.lang.annotation.Target;
import java.util.Optional;

public class OptionalTest2 {

    @Test
    public void test1(){
        Optional