Optional类的使用举例

最新推荐文章于 2024-09-17 11:50:15 发布

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本文介绍了Java中的Optional类，用于避免空指针异常。通过示例展示了Optional.of()、Optional.ofNullable()、orElse()等方法的用法，并在Boy和Girl类的示例中应用Optional来优化代码，提高程序安全性。

Boy类：
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：
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 + '\'' +
                '}';
    }
}

/*
 Optional类：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();
        //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;
        //ofNullable(T t):t可以为null
        Optional<Girl> 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t是空的，则返回orElse()方法中的参数t1
        Girl girl1 = optionalGirl.orElse(new Girl("李知恩"));
        System.out.println(girl1);
    }

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

    @Test
    public void test3(){
        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){
            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);
        //此时的boy1一定非空
        Boy boy1 = boyOptional.orElse(new Boy(new Girl("李知恩")));

        Girl girl = boy1.getGirl();
        Optional<Girl> girlOptional = Optional.ofNullable(girl);
        //girl1一定非空
        Girl girl1 = girlOptional.orElse(new Girl("李知恩"));

        return girl1.getName();
    }

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

}