Optional.of(T t) : 創(chuàng)建一個(gè) Optional 實(shí)例
Optional.empty() : 創(chuàng)建一個(gè)空的 Optional 實(shí)例
Optional.ofNullable(T t) : 若 t 不為 null，創(chuàng)建 Optional 實(shí)例；否則創(chuàng)建空實(shí)例
isPresent() : 判斷是否包含值
orElse(T t) : 如果調(diào)用對(duì)象包含值，返回該值，否則返回t
orElseGet(Supplier s) : 如果調(diào)用對(duì)象包含值，返回該值，否則返回 s 獲取的值
map(Function f) : 如果有值對(duì)其處理，并返回處理后的Optional，否則返回 Optional.empty()
flatMap(Function mapper) : 與 map 類似，要求返回值必須是Optional

2.應(yīng)用舉例

下面的代碼案例按照上面所列方法順序給出。首先需要一個(gè)Employee類用作測(cè)試。

package com.szh.java8;
 
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
 
/**
 *
 */
@Data
@NoArgsConstructor
@AllArgsConstructor
public class Employee {
 
    private Integer id;
    private String name;
    private Integer age;
    private Double salary;
 
}

    @Test
    public void test1() {
        Optional<Employee> op = Optional.of(new Employee());
        Employee employee = op.get();
        System.out.println(employee);
    }

    @Test
    public void test2() {
        Optional<Employee> op = Optional.empty();
        System.out.println(op.get());
    }

    @Test
    public void test3() {
        Optional<Employee> op = Optional.ofNullable(new Employee(1001,"張起靈",18,6666.66));
        System.out.println(op.get());
    }

    @Test
    public void test4() {
        Optional<Employee> op = Optional.of(new Employee());
        if (op.isPresent()) {
            System.out.println(op.get());
        }
    }

    @Test
    public void test5() {
        Optional<Employee> op1 = Optional.ofNullable(null);
        Employee employee1 = op1.orElse(new Employee(1001,"張起靈",18,6666.66));
        System.out.println(employee1);
 
        Optional<Employee> op2 = Optional.ofNullable(new Employee());
        Employee employee2 = op2.orElse(new Employee(1001,"張起靈",18,6666.66));
        System.out.println(employee2);
    }

    @Test
    public void test6() {
        Optional<Employee> op1 = Optional.ofNullable(null);
        Employee employee1 = op1.orElseGet(() -> new Employee(1001,"張起靈",18,6666.66));
        System.out.println(employee1);
 
        Optional<Employee> op2 = Optional.ofNullable(new Employee());
        Employee employee2 = op2.orElseGet(() -> new Employee(1001,"張起靈",18,6666.66));
        System.out.println(employee2);
    }

    @Test
    public void test7() {
        Optional<Employee> op1 = Optional.of(new Employee(1001,"張起靈",18,6666.66));
 
        Optional<String> op2 = op1.map(Employee::getName);
        System.out.println(op2.get());
 
        Optional<String> op3 = op1.flatMap((e) -> Optional.of(e.getName()));
        System.out.println(op3.get());
    }