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@FunctionalInterface
interface GreetingService 
{
    void sayMessage(String message);
}

GreetingService greetService1 = message -> System.out.println("Hello " + message);

import java.util.Arrays;
import java.util.List;
import java.util.function.Predicate;

public class Java8Tester {
   public static void main(String args[]){
      List<Integer> list = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9);

      // Predicate<Integer> predicate = n -> true
      // n is a parameter passed to the test method of the Predicate interface
      // If n exists, the test method returns true

      System.out.println("Print all numbers:");

      // Pass parameter n
      eval(list, n->true);

      // Predicate<Integer> predicate1 = n -> n%2 == 0
      // n is a parameter passed to the test method of the Predicate interface
      // If n%2 is 0, the test method returns true

      System.out.println("Print all even numbers:");
      eval(list, n-> n%2 == 0 );

      // Predicate<Integer> predicate2 = n -> n > 3

// n is a parameter passed to the test method of the Predicate interface
// The test method returns true if n is greater than 3

System.out.println("Output all numbers greater than 3:");
eval(list, n -> n > 3);
}

public static void eval(List<Integer> list, Predicate<Integer> predicate) {
   for (Integer n : list) {

      if (predicate.test(n)) {
         System.out.println(n + " ");
      }
   }
}
}

$ javac Java8Tester.java 
$ java Java8Tester
Output all data:
1 
2 
3 
4 
5 
6 
7 
8 
9 
Output all even numbers:
2 
4 
6 
8 
Output all numbers greater than 3:
4 
5 
6 
7 
8 
9