Pattern Matching for instanceof in Java

Java 14 introduces instanceof operator to have type test pattern as is a preview feature. Type test pattern has a predicate to specify a type with a single binding variable. It is a standard feature of Java from Java 17 onwards.

Syntax with Enhanced instanceof operator

In following code snippet, we've used instanceof operator to test person object being an Employee as well assign person object to Employee reference e which is then used to perform operation on Employee object.

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

Before this enhancement, developers have to typecast the object as shown below:

Syntax without Enhanced instanceof operator

In following code snippet, we're showing regular approach of testing person object with Employee class and then in if block, we're typecasting the person to Employee e to perform operation on Employee object.

if (person instanceof Employee) {
   // Unnecessary casting
   Employee e = (Employee)person;
   return e.getEmployeeId();
}

Example - Old Syntax

In this example, we've defined classes Person, Employee and Manager. Employee and Manager extends Person class. In APITester class, we've defined a method getId() which takes Person as input and using instanceof operator, we're testing the type of object as either Employee or Manager and then based on the result of if block, we're typecasting the object to either Employee or Manager and return the employeeId or managerId accordingly.

package com.tutorialspoint;

public class APITester {
   public static void main(String[] args) {
      // Create a Manager Instance   
      Person manager = new Manager(23, "Robert");
      // Get and print Id of the manager
      System.out.println(getId(manager));
   }
   // using instanceof operator
   // to test type of Person to be Employee or Manager
   public static int getId(Person person) {
      // If person is Employee, assign it to e
      // in next statement	  
      if (person instanceof Employee) {
         // Unnecessary typecasting	  
         Employee e = (Employee)person;	  
         return e.getEmployeeId();
      } 
      // If person is Manager, assign it to m
      // in same statement	
      else if (person instanceof Manager) {
         // Unnecessary typecasting	  
         Manager m = (Manager)person;
         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;
   }
}

Output

Let us compile and run the above program, this will produce the following result −

23

Example - New Syntax

In this example, we've defined classes Person, Employee and Manager. Employee and Manager extends Person class. In APITester class, we've defined a method getId() which takes Person as input and using instanceof operator, we're testing the type of object as either Employee or Manager and then within same if block, we're assigning the object to either Employee or Manager without typecasting and return the employeeId or managerId accordingly.

package com.tutorialspoint;

public class APITester {
   public static void main(String[] args) {
      // Create a Manager Instance   
      Person manager = new Manager(23, "Robert");
      // Get and print Id of the manager
      System.out.println(getId(manager));
   }
   // using instanceof operator
   // to test type of Person to be Employee or Manager
   public static int getId(Person person) {
      // If person is Employee, assign it to e
      // in same statement	  
      if (person instanceof Employee e) {
         return e.getEmployeeId();
      } 
      // If person is Manager, assign it to m
      // in same statement	
      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;
   }
}

Output

Let us compile and run the above program, this will produce the following result −

23