Optional<T> 类(java.util.Optional) 是一个容器类，代表一个值存在或不存在，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。
常用方法 ：
下面的代码案例按照上面所列方法顺序给出。首先需要一个Employee类用作测试。
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,"张起灵",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,"张起灵",18,6666.66));
System.out.println(employee1);
Optional<Employee> op2 = Optional.ofNullable(new Employee());
Employee employee2 = op2.orElse(new Employee(1001,"张起灵",18,6666.66));
System.out.println(employee2);
}
@Test
public void test6() {
Optional<Employee> op1 = Optional.ofNullable(null);
Employee employee1 = op1.orElseGet(() -> new Employee(1001,"张起灵",18,6666.66));
System.out.println(employee1);
Optional<Employee> op2 = Optional.ofNullable(new Employee());
Employee employee2 = op2.orElseGet(() -> new Employee(1001,"张起灵",18,6666.66));
System.out.println(employee2);
}
@Test
public void test7() {
Optional<Employee> op1 = Optional.of(new Employee(1001,"张起灵",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());
}
