In this example we shall show you how to use the for-each loop.
This new way of iteration was introduced in Java 5 and offers a more convenient way of iterating over arrays and collections. It is an extension to the classic for loop and it is widly known as “enhanced for” or “for-each”. The phrase “for-in loop” is also used, but less often.
The main difference between the classic for loop and the new loop is the fact that it hides the iteration variable. As a result, usage of the for-each loop leads to a more readable code with one less variable to consider each time we want to create a loop thus the possibility of ending up with a logic error is smaller.
However, hiding the iterator has some drawbacks as well. For instance, we cannot use it to remove or replace items in a list and iteration over multiple collections in parallel is not possible. This means that it cannot replace the classic for loop everywhere. We can use it whenever access to only a single element in each iteration is needed.
We can use it over both arrays and collections, as well as over any class that implements the interface Iterable.
1. Syntax
The syntax of this new loop is very simple since it hides the iterator.
- To iterate over the containts of an array:
for (type variable: Array){} - To iterave over the elements of a colletion:
for (type variable: Collection){}
2. Example 1
The following example demonstrates the use of for-each loop in different occasions:
foreachExample.java:
package com.javacodegeeks.core.for_each;
import java.util.ArrayList;
import java.util.List;
public class foreachExample {
public static void main(String Args[]) {
// Example 1
System.out.println("Example 1");
// Using for-each over a single dimension Array
int myArray[] = { 1, 2, 3, 4, 5 };
for (int var : myArray) {
System.out.println(var);
}
// Example 2
System.out.println("Example 2");
// Using for-each over a two dimensions Array
// we create an Array and initialize it using the classic for loop
int myArray2[][] = new int[2][2];
for (int i = 0; i < 2; i++) {
for (int j = 0; j < 2; j++) {
myArray2[i][j] = i + j;
}
}
// we print all its values using the for-each loop
for (int[] x : myArray2) {
for (int y : x) {
System.out.println(y);
}
}
// Example 3
System.out.println("Example 3");
// Using for-each over a Collection
// We create and initialize our list
List myArrayList = new ArrayList();
myArrayList.add("A");
myArrayList.add("B");
myArrayList.add("C");
// we print all its values using the for-each loop
for (String str : myArrayList)
System.out.println(str);
}
}
Output:
Example 1 1 2 3 4 5 Example 2 0 1 1 2 Example 3 A B C
3. Example 2
The following example demonstrates how to use for-each example in your own class. As mentioned above, all we have to do to is implement the interface Iterable in our class. The following class ClassRoom implements the interface, so we can use the for-each loop to iterate over the students names that are inside each room.
ClassRoom.java:
package com.javacodegeeks.core.for_each;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.NoSuchElementException;
public class ClassRoom implements Iterable, Iterator {
ArrayList students;
int count = 0;
public ClassRoom() {
// We initialize our ClassRoom with a few random Students
students = new ArrayList();
students.add("Tom");
students.add("Mike");
students.add("John");
students.add("John");
students.add("Bill");
}
@Override
public Iterator iterator() {
count = 0;
return this;
}
@Override
public boolean hasNext() {
if (count < students.size()) {
return true;
}
return false;
}
@Override
public String next() {
if (count == students.size())
throw new NoSuchElementException();
return students.get(count++);
}
@Override
public void remove() {
// TODO Auto-generated method stub
}
public static void main(String Args[]) {
// we create our ClassRoom's instance
ClassRoom room_A = new ClassRoom();
// We use for-each loop to print all students names in the classroom
for (String str : room_A) {
System.out.println(str);
}
}
}Output:
Tom Mike John John Bill
Download Source Code
This was an example of using for-each loop in Java.
Download the Eclipse project of this example: ForEachExample.zip
