Java 15 instanceof的模式匹配

Java 14引入了instanceof运算符作为预览特性，以具有类型测试模式。类型测试模式具有一个谓词来指定一个带有单个绑定变量的类型。在Java 15中，它仍然是一个预览特性。

语法

if (person instanceof Employee e) {   return e.getEmployeeId();}

示例

考虑以下示例 –

ApiTester.java

public class APITester {   public static void main(String[] args) {      Person manager = new Manager(23, "Robert");      manager.name = "Robert";      System.out.println(getId(manager));   }   public static int getId(Person person) {      if (person instanceof Employee e) {         return e.getEmployeeId();      }       else if (person instanceof Manager m) {         return m.getManagerId();      }      return -1;   }}abstract sealed class Person permits Employee, Manager {   String name;   String getName() {      return name;   }}final class Employee extends Person {   String name;   int id;   Employee(int id, String name){      this.id = id;      this.name = name;   }   int getEmployeeId() {      return id;   }}non-sealed class Manager extends Person {   int id;   Manager(int id, String name){      this.id = id;      this.name = name;   }   int getManagerId() {      return id;   }}

编译和运行程序

$javac -Xlint:preview --enable-preview -source 14 APITester.java$java --enable-preview APITester

输出

23