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);
    }
}

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 +
                '}';
    }
}

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 + '\'' +
                '}';
    }
}