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Arrays

Iterating Through Arrays

Looping through an array means going through each item in the array. There are two common ways to do this in Java.

Using a For Loop:

String[] friends = {"Rahul", "Simran", "Kiran", "Naina", "Aman"};
for (int i = 0; i < friends.length; i++) {
  System.out.println(friends[i]);
}

This code uses a for loop. It's like saying, "Start from the first name, go up to the last name, and print each one."

Using a For-Each Loop:

String[] friends = {"Rahul", "Simran", "Kiran", "Naina", "Aman"};
for (String friend : friends) {
  System.out.println(friend);
}

This code uses a for-each loop. It's simpler. It says, "For each car in the list, print it." No need to worry about counting or length.

Here's what's happening:

  • for is like saying "Let's do something repeatedly."
  • friends is the name of our array with some names in it.
  • String friend is like a temporary box to hold each string as we look at them one by one.

So, what happens in each round of the loop:

  • 1st time: It looks at the first name (Rahul) and prints it.
  • 2nd time: It looks at the second name (Simran) and prints it.
  • 3rd time: It looks at the third name (Kiran) and prints it.
  • 4th time: It looks at the fourth name (Naina) and prints it.
  • 5th time: It looks at the fifth name (Aman) and prints it.

That's it! The for-each loop makes it easy to check out all the names in an array without getting into the nitty-gritty details of the array's size and index. It's like saying, "Hey, show me each number, one at a time!"

Practice problem

Write a Java program to display the sum of all the elements in an array.

Input

Array size - 7
1 2 3 4 5 6 7

Output

Sum of all the elements - 28
Approach1 using a for loop 
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        int size, sum = 0;

        // Create a Scanner object for user input
        Scanner scanner = new Scanner(System.in);

        // Ask the user for the size of the array
        System.out.print("Enter the size of the array: ");
        size = scanner.nextInt();

        // Create an array to store user-input elements
        int array[] = new int[size];

        // Prompt the user to enter array elements
        System.out.println("Enter array elements:");

        // Loop to get input elements and calculate the sum
        for (int i = 0; i < size; i++) {
            array[i] = scanner.nextInt();
            sum = sum + array[i];
        }

        // Display the sum of the array
        System.out.println("Sum of the array is: " + sum);
    }
}
Approach2 using a for-each loop 
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        int size;

        // Create a Scanner object for user input
        Scanner scanner = new Scanner(System.in);

        // Ask the user for the size of the array
        System.out.print("Enter the size of the array: ");
        size = scanner.nextInt();

        // Create an array to store user-input elements
        int array[] = new int[size];

        // Prompt the user to enter array elements
        System.out.println("Enter array elements:");

        // Loop to get input elements and calculate the sum
        for (int i = 0; i < size; i++) {
            array[i] = scanner.nextInt();
        }

        int sum = 0;
		for(int num : array){
		   sum = sum + num;
		}

        // Display the sum of the array
        System.out.println("Sum of the array is: " + sum);
    }
}