避免空指针异常。
package com.expgiga.Java8; import java.util.Optional; /** * */ public class TestOptional { /* * Optional.of(T t):创建实例 * Optional.empty():创建一个空的Optional实例 * Optional.ofNullable(T t):若t不为null，创建Optional实例，否则创建空实例 * isPresent():判断是否包含值 * orElse(T t):如果调用对象包含值，返回该值，否则返回t * orElseGet(Supplier s):如果调用对象包含该值，返回该值，否则返回s获取的值 * map(Function f):如果有值对其处理，并返回处理后的Optional，否则返回Optional.empty() * flatMap(Function mapper):与map类似，要去返回值必须是Optional * */ public static void main(String[] args) { Optional<Employee> op = Optional.of(new Employee()); System.out.println(op.get()); Optional<Employee> op1 = Optional.empty(); System.out.println(op1.get()); Optional<Employee> op2 = Optional.ofNullable(new Employee()); System.out.println(op2.get()); Optional<Employee> op3 = Optional.ofNullable(null); if (op3.isPresent()) { System.out.println(op3.get()); } Employee emp = op3.orElse(new Employee("ss", 16, 2000, Employee.Status.FREE)); System.out.println(emp); Employee emp1 = op3.orElseGet(() -> new Employee()); System.out.println(emp1); //map Optional<Employee> op4 = Optional.ofNullable(new Employee("ss", 16, 2000, Employee.Status.FREE)); Optional<String> str = op4.map((e) -> e.getName()); System.out.println(str.get()); //flatMap Optional<String> str2 = op4.flatMap((e) -> Optional.of(e.getName())); System.out.println(str2.get()); } }
