Use Java 8's New Predicate To Manipulate Collections

Java 8 introduced functional interfaces and lambda expressions to simplify the manipulation of collections. One such functional interface is Predicate, which represents a boolean-valued function of one argument. You can use Predicate along with the Stream API and lambda expressions to filter, modify, or query collections in a more concise and readable way. Here's a tutorial on using Java 8's Predicate to manipulate collections.

Import necessary classes:

First, import the necessary classes from the java.util and java.util.function packages.

import java.util.ArrayList;
import java.util.List;
import java.util.function.Predicate;
import java.util.stream.Collectors;

Create a sample collection:

Create a sample collection, such as a List of integers, to demonstrate the use of Predicate.

List<Integer> numbers = new ArrayList<>();
numbers.add(1);
numbers.add(2);
numbers.add(3);
numbers.add(4);
numbers.add(5);

Define a Predicate:

Define a Predicate using a lambda expression. For example, create a predicate that checks whether a number is even.

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

Filter a collection using a Predicate:

You can use the Stream API's filter() method along with a Predicate to filter elements in a collection. For example, create a new list containing only the even numbers from the numbers list.

List<Integer> evenNumbers = numbers.stream()
                                   .filter(isEven)
                                   .collect(Collectors.toList());

System.out.println(evenNumbers); // Output: [2, 4]

Combine multiple Predicates:

You can also combine multiple predicates using the and(), or(), and negate() methods. For example, create two predicates to check whether a number is even and greater than 2, and then filter the list using both predicates.

Predicate<Integer> isEven = n -> n % 2 == 0;
Predicate<Integer> greaterThanTwo = n -> n > 2;

// Combine predicates
Predicate<Integer> evenAndGreaterThanTwo = isEven.and(greaterThanTwo);

List<Integer> filteredNumbers = numbers.stream()
                                       .filter(evenAndGreaterThanTwo)
                                       .collect(Collectors.toList());

System.out.println(filteredNumbers); // Output: [4]

This tutorial demonstrated how to use Java 8's Predicate functional interface and the Stream API to manipulate collections. By leveraging Predicate and lambda expressions, you can write more concise and readable code when filtering, modifying, or querying collections.