Importance of Predicate Interface in Lambda Expression in Java

Predicate<T> is a generic functional interface that represents a single argument function that returns a boolean value (true or false). This interface available in java.util.function package and contains a test(T t) method that evaluates the predicate of a given argument.

Syntax

public interface Predicate {
 boolean test(T t);
}

Example

import java.util.*;
import java.util.functionPredicate;

public class LambdaPredicateTest {
   public static void main(String args[]) {
      Employee emp1 = new Employee("Raja", 26);
      Employee emp2 = new Employee("Jaidev", 24);
      Employee emp3 = new Employee("Adithya", 30);

      List<Employee> empList = new ArrayList<Employee>();
      empList.add(emp1);
      empList.add(emp2);
      empList.add(emp3);

      Predicate<Employee> predicateForAge = (e) -> e.age >= 25;
      Predicate<Employee> predicateForName = (e) -> e.name.startsWith("A");
      for(Employee emp : empList) {
         if(predicateForAge.test(emp)) {
            System.out.println(emp.name +" is eligible by age");
         }
      }
      System.out.println("----------------------------");
      for(Employee emp : empList) {
         if(predicateForName.test(emp)) {
            System.out.println(emp.name +" is eligible by name");
         }
      }
   }
}

// Employee class
class Employee {
   public String name;
   public int age;
   public Employee(String name,int age){
      this.name=name;
      this.age=age;
   }
}

Output

Raja is eligible by age
Adithya is eligible by age
----------------------------
Adithya is eligible by name