🔍 What is a Predicate?

A Predicate in Java is a functional interface that represents a boolean-valued function (i.e., it returns true or false) for a single input.

✅ Used mainly in filtering, validations, and conditional logic, especially in Streams and Lambdas.

📦 Predicate Interface Declaration

@FunctionalInterface
public interface Predicate<T> {
    boolean test(T t);
}

  • It’s in the package: java.util.function.Predicate

🧪 Basic Example

Predicate<Integer> isEven = x -> x % 2 == 0;

System.out.println(isEven.test(10)); // true
System.out.println(isEven.test(7));  // false

🔁 Using Predicate with Streams

List<String> names = Arrays.asList("Aftab", "Nitin", "Ankit", "Neha");

Predicate<String> startsWithA = name -> name.startsWith("A");

names.stream()
     .filter(startsWithA)
     .forEach(System.out::println);
// Output: Aftab, Ankit

🔗 Predicate Methods

Method Description Example
test(T t) Returns true or false isEven.test(4) → true
and(Predicate other) Combines two predicates with logical AND isEven.and(gtTen)
or(Predicate other) Combines with logical OR isEven.or(gtTen)
negate() Reverses the condition isEven.negate()
isEqual(Object o) Static method to check equality Predicate.isEqual("test")

🧠 Example with and():

Predicate<Integer> isEven = x -> x % 2 == 0;
Predicate<Integer> gtTen = x -> x > 10;

Predicate<Integer> evenAndGT10 = isEven.and(gtTen);

System.out.println(evenAndGT10.test(12)); // true
System.out.println(evenAndGT10.test(8));  // false

✅ Summary

Feature Value
Type Functional Interface
Package java.util.function
Method boolean test(T t)
Use Cases Filters, validations, conditions
Lambda-Friendly ✅ Yes
Back to blog

Leave a comment

Please note, comments need to be approved before they are published.