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Java forEach

 Java, forEach is a method introduced in Java 8 in the Iterable interface. It's a part of the Stream API and provides a way to iterate over elements of a collection and perform an action on each element. It takes a functional interface as an argument, typically a lambda expression or a method reference, which represents the action to be performed on each element.

Here's the syntax of forEach method:

void forEach(Consumer<? super T> action)

Where:

  • action is the action to be performed for each element.
  • Consumer is a functional interface from the java.util.function package. It represents an operation that accepts a single input argument and returns no result.

Let's see some examples:

Example 1: Basic usage with ArrayList

import java.util.ArrayList; public class ForEachExample {
public static void main(String[] args) { ArrayList<String> names =
ArrayList<String> names = new ArrayList<>(); names.add(
 names.add("Alice"); names.add(
 names.add("Bob"); names.add(
 names.add("Charlie");

// Using forEach to print each name
 names.forEach(name -> System.out.println(name));
 }
}

Example 2: Using method reference

import java.util.ArrayList; public class ForEachExample {
public static void main(String[] args) { ArrayList<Integer> numbers =
ArrayList<Integer> numbers = new ArrayList<>(); numbers.add(
 numbers.add(1); numbers.add(
 numbers.add(2); numbers.add(
 numbers.add(3);

// Using forEach with method reference to print each number
 numbers.forEach(System.out::println);
 }
}

Example 3: Modifying elements

import java.util.ArrayList; public class ForEachExample {
public static void main(String[] args) { ArrayList<Integer> numbers =
ArrayList<Integer> numbers = new ArrayList<>(); numbers.add(
 numbers.add(1); numbers.add(
 numbers.add(2); numbers.add(
 numbers.add(3);

// Using forEach to double each number
 numbers.forEach(num -> System.out.println(num * 2)); } }
 }
}


Example 4: Using custom functional interface

import java.util.ArrayList; import java.util.function.Consumer; public class ForEachExample {
public static void main(String[] args) { ArrayList<String> names =
ArrayList<String> names = new ArrayList<>(); names.add(
 names.add("Alice"); names.add(
 names.add("Bob"); names.add(
 names.add("Charlie");

// Custom functional interface for printing names
 Consumer<String> printName = name -> System.out.println("Name: " + name);

// Using forEach with custom functional interface
 names.forEach(printName);
 }
}

In each of these examples, the forEach method is used to iterate over the elements of a collection (ArrayList in these cases) and perform specific actions on each element.

It provides a concise and expressive way to perform operations on collections in Java.



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