Java 8 forEach() Method
Java 8 forEach() method defined in Iterable interface. It is used to iterate over collections such as Sets, Lists, and Maps in a readable and concise way. It was introduced as part of the functional programming features in Java 8, allows us to directly pass actions such as Method references or Lambda expressions. Instead of writing long loops, we can use forEach() along with a lambda expression to perform operations on each element.
Syntax:
- default:The default keyword means the method has a default implementation inside the interface.
- void: The void keywordrepresents the return type of the method. The forEach() method does not return any value; it only performs an action on each element.
- forEach:It is the method name. It indicates that the method performs an operation on each element of the collection.
- (Consumer<? super T> action): It is a parameter of the method. It is a functional interface belongs to the java.util.function package. It accepts an argumentand returns no result. We usually pass a lambda expression
Example: Iterating Over List
The following Java program demonstrates how to use Java 8's forEach() method with a lambda expression to iterate through an ArrayList.
Java
import java.util.ArrayList;
import java.util.List;
public class Main {
// main method
public static void main(String[] args) {
List gamesList = new ArrayList(); // Creating a new ArrayList to store games
// Adding games to the list
gamesList.add("Football");
gamesList.add("Cricket");
gamesList.add("Chess");
gamesList.add("Hockey");
// Printing a separator
System.out.println("------------Iterating by passing lambda expression--------------");
// Iterating over the list using forEach and printing each element using a lambda expression
gamesList.forEach(game -> System.out.println(game));
}
}
Output:
------------Iterating by passing lambda expression-------------- Football Cricket Chess Hocky
Example: Iterating Over Map
The following Java program demonstrates how to use a HashMap and the forEach() method with a lambda expression to iterate through all key-value pairs.
Java
import java.util.HashMap;
import java.util.Map;
public class Main {
// main method
public static void main(String[] args) {
// creating a HashMap
Map map = new HashMap<>();
map.put("A1", 110);
map.put("B1", 210);
map.put("C1", 310);
map.put("D1", 410);
map.put("E1", 510);
map.put("F1", 610);
// for each using lambda
map.forEach((k, v) -> System.out.println("Key : " + k + ", Value : " + v));
}
}
Output:
Key : A1, Value : 110 Key : F1, Value : 610 Key : E1, Value : 510 Key : D1, Value : 410 Key : C1, Value : 310 Key : B1, Value : 210
Example: Using forEach() Method with Consumer Interface
This Java program demonstrates how to use a Consumer functional interface with both a List and a Stream to convert strings into their hexadecimal character representations.
Java
import java.util.function.Consumer;
import java.util.*;
import java.util.stream.Stream;
public class Main {
// main method
public static void main(String[] args) {
List list1 = Arrays.asList("def", "Python", "Java");
Stream stream1 = Stream.of("def", "Python", "Java");
// convert a String to a Hexadecimal
Consumer displayTextInHexConsmer = (String s) -> {
StringBuilder sbObj = new StringBuilder();
for (char ch : s.toCharArray()) {
String h = Integer.toHexString(ch);
sbObj.append(h);
}
System.out.print(String.format("%n%-10s:%s", s, sbObj.toString()));
};
// passing a Consumer
list1.forEach(displayTextInHexConsmer);
stream1.forEach(displayTextInHexConsmer);
}
}
Output:
def :646566 python :707974686f6e Java :6a617661 def :646566 Python :707974686f6e Java :6a617661
Example: Using forEach() with Method Reference
In this example, the forEach() method uses a method reference instead of a lambda expression.
Java
import java.util.List;
import java.util.ArrayList;
public class Main {
public static void main(String[] args) {
List gamesList = new ArrayList();
gamesList.add("Football");
gamesList.add("Cricket");
gamesList.add("Chess");
gamesList.add("Hockey");
//iterating over list
gamesList.forEach(System.out::println);
}
}
Output:
Football Cricket Chess Hockey
Java forEach() Method Vs. Traditional Loop
| Feature | forEach() Method | Traditional Loop (for, while) |
|---|---|---|
| Paradigm | It is declarative (we state what to do). | It is imperative (we state how to do it). |
| Control Flow | It does not support break or continue statement. | It supports break, continue, and return statement. |
| Data Scope | It creates a new block scope for each callback. | It shares the same scope across all iterations. |
| Asynchronous Behavior | It does not wait for async/await promises. | It seamlessly supports async/await step-by-step. |
| Applicability | It is specific to arrays or collections. | It is used for general purpose. It can run without a collection. |
| Performance | It is slightly slower due to function call overhead. | It is faster, highly optimized by compilers. |
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