[Java知识库]Java学习(尚硅谷)Optional类学习

package com.atguigu.java3;

import org.junit.Test;

import java.util.Optional;

/**
 * Optional类：为了在程序中避免空指针异常而出现的
 * 常用方法：ofNullable(T t)
 *          orElse(T t)
 * @author 
 * @create 2022-05-09-9:53
 */
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<Girl> optionalGirl = Optional.of(girl);//of(T t)必须保证t是非空的

        Optional<Girl> girl1 = Optional.ofNullable(girl);//ofNullable(T t):t可以为null
        System.out.println(girl1);//Optional.empty
        //orElse(T t):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t是空的，则返回
        //orElse()方法中的t.
        Girl girl2 = girl1.orElse(new Girl("小红"));
        System.out.println(girl2);

    }

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

    @Test
    public void test2(){
        Boy boy = new Boy();
        String girlName = getGirlName(boy);
        System.out.println(girlName);
    }


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

    //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);
        //girl1一定非空
        Girl girl1 = girlOptional.orElse(new Girl("古力娜扎"));

        return girl1.getName();
    }

    @Test
    public void test3(){
        Boy boy=null;
        boy=new Boy();

        String girlName = getGirlName2(boy);
        System.out.println(girlName);

    }

}

package com.atguigu.java3;

/**
 * @author 
 * @create 2022-05-09-9:50
 */
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 +
                '}';
    }
}

package com.atguigu.java3;

/**
 * @author 
 * @create 2022-05-09-9:51
 */
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 + '\'' +
                '}';
    }
}

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