# Java8之Optional类

**Repository Path**: fpfgitmy_admin/java8-optional-class

## Basic Information

- **Project Name**: Java8之Optional类
- **Description**: No description available
- **Primary Language**: Unknown
- **License**: Not specified
- **Default Branch**: master
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 1
- **Forks**: 0
- **Created**: 2021-04-28
- **Last Updated**: 2021-04-28

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

### Java8之Optional类
+ Optional<T> 类(java.util.Optional)是一个容器类,它可以保存类型T的值,代表这个值存在.后者仅仅保存null,表示这个值不存在。将原来用null表示一个值不存在，现在Optional可以更好的表达这个概念。并且可以避免空指针异常

#### Optional类的方法

| 返回值 | 方法 | 示意 | 扩展 |
| --- | --- | --- | --- |
| static <T> Optional<T> | of(T value) | 创建一个Optional实例,t必须非空 | - |
| static<T> Optional<T> | empty() | 创建一个空的Optional实例 | - |
| static <T> Optional<T> | ofNullable(T value) |创建一个Optional实例,t可以为null  | - |
| boolean | isPresent() | 判断是否包含对象 | - |
| void | ifPresent(Consumer<? super T> consumer) | 如果有值,就执行Consumer接口的实现代码,别该值会作为参数传给它 | - |
| T | get() | 如果Optional容器对象包含值,返回该值,否则抛异常 | - |
| T | orElse(T other) | 如果Optional容器对象有值则将其返回,否则返回其指定的other对象 | - |
| T | orElseGet(Supplier<? extends T> other) | 如果Optional容器有值则将其返回,否则返回由Supplier接口实现提供的对象 | - |
| <X extends Throwable> T | orElseThrow(Supplier<? extends X> exceptionSupplier) throws X | 如果Optional容器有值则返回,否则抛出由Supplier接口实现提供的异常 | - |

##### 代码示例

+ 提供的model
```
public class Boy {

    private Girl girl;

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

    public Boy() {

    }

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

    public Girl getGirl() {
        return girl;
    }

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

```
public class Girl extends Boy{

    private String name;

    public String getName() {
        return name;
    }

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

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

    public Girl() {
    }

    @Override
    public String toString() {
        return "Girl{" +
                "name='" + name + '\'' +
                '}';
    }
}
```
+ 实际操作的代码

```
    @Test
    public void test1() {
        Girl girl = new Girl();
        Optional<Girl> og = Optional.of(girl);
        System.out.println("创建参数不能为空的实例" + og.get());
        System.out.println("------------------------------");
        girl = null;
        Optional<Girl> og1 = Optional.ofNullable(girl);
        System.out.println("创建参数可以为空的实例" + og1);
        System.out.println("------------------------------");

    }

    public String getGirlName(Boy boy) {
        //Java8之前写法
        if (boy != null) {
            if (boy.getGirl() != null) {
                return boy.getGirl().getName();
            }
        }
        return null;
    }

    public String getGirlNameForJDK8(Boy boy) {
        // Java8写法
        Optional<Boy> ob = Optional.ofNullable(boy);
        // 此时的boy1一定非空
        Boy boy1 = ob.orElse(new Boy(new Girl("哈哈哈")));
        Girl girl = boy1.getGirl();
        Optional<Girl> oj = Optional.ofNullable(girl);
        // 此时的girl1一定非空
        Girl girl1 = oj.orElse(new Girl("滴滴滴"));
        return girl1.getName();
    }

    @Test
    public void test2() {
        // 情况1：实例非null
        Boy boy = new Boy();
        String girlName = getGirlName(boy);
        System.out.println("Java8之前的写法" + girlName);
        System.out.println("------------------------------");
        // 情况2：实例是null
        //boy = null;
        // 情况3：实例有值
        boy = new Boy(new Girl("贷款的贷款"));
        String girlNameForJDK8 = getGirlNameForJDK8(boy);
        System.out.println("Java8的写法" + girlNameForJDK8);
    }

```