java8新特性：Optional类

Optional类

• ​​代码​​

• ​​OptionalTest类​​
• ​​Boy类​​
• ​​Girl类​​

• ​​图片​​

总结于​​尚硅谷​​学习视频
​​​视频链接​​​​ https://www.bilibili.com/video/BV1Kb411W75N?p=685​​

代码

OptionalTest类

package com.day0330_1;

import org.junit.jupiter.api.Test;

import java.util.Optional;

/**
 * 为了在程序中避免出现空指针异常而创建的
 *
 * 常用的方法：ofNullable(T t)
 *          orElse(T t)
 */
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;//NullPointerException
        //of(T t)：保证t是非空的
        Optional<Girl> optionalGirl = Optional.of(girl);

    }

    @Test
    public void test2(){
        Girl girl = new Girl();
        girl=null;//NullPointerException
//        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<Boy> boyOptional = Optional.ofNullable(boy);

        //此时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);

        //此时girl1一定非空
        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);

    }

}

Boy类

package com.day0330_1;

public class Boy {
    private Girl girl;

    public Boy() {
    }

    public Boy(Girl girl) {
        this.girl = girl;
    }

    public Girl getGirl() {
        return girl;
    }

    public void setGirl(Girl girl) {
        this.girl = girl;
    }

    @Override
    public String toString() {
        return "Boy{" +
                "girl=" + girl +
                '}';
    }

}

Girl类

package com.day0330_1;


public class Girl {
    private String name;

    public Girl() {
    }

    public Girl(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Girl{" +
                "name='" + name + '\'' +
                '}';
    }
}

图片