Course:
Learn Java Programming
[post-views]
In this lesson, you will learn.
for loop in Java is a control flow statement that allows code to be executed repeatedly for a certain number of times, based on a given condition.
Note: The for loop is often used when the number of iterations is known before entering the loop.
Note: While loop is preferred when the number of iterations is not known beforehand or depends on dynamic conditions.
Syntax
for (initialization; condition; update) {
// Statements to be executed
}
package ch5;
public class SimpleCounter {
public static void main(String[] args) {
for (int i = 0; i < 5; i++) {
System.out.println("Count: " + i);
}
}
}
Output
Count: 0
Count: 1
Count: 2
Count: 3
Count: 4
This loop prints numbers from 0 to 4. The loop initializes i to 0 and increments it by 1 each time until it reaches 4.
package ch5;
public class SumOfNumbers {
public static void main(String[] args) {
int sum = 0;
for (int i = 1; i <= 10; i++) {
sum += i;
}
System.out.println("Sum: " + sum);
}
}
Output
Sum: 55
This loop calculates the sum of numbers from 1 to 10.
package ch5;
public class ReverseLoop {
public static void main(String[] args) {
for (int i = 10; i > 0; i--) {
System.out.println("Reverse Count: " + i);
}
}
}
Output
Reverse Count: 10
Reverse Count: 9
Reverse Count: 8
Reverse Count: 7
Reverse Count: 6
Reverse Count: 5
Reverse Count: 4
Reverse Count: 3
Reverse Count: 2
Reverse Count: 1
This loop counts down from 10 to 1, decrementing i in each iteration.
package ch5;
public class LoopinString {
public static void main(String[] args) {
String greeting = "Hello";
for (int i = 0; i < greeting.length(); i++) {
System.out.println(greeting.charAt(i));
}
}
}
Output
H
e
l
l
o
This loop prints each character of the string “Hello”.
In Java, you can use multiple statements in the initialization and update parts of a for loop by separating them with commas.
Note: This is useful when you need to work with multiple variables within the loop. However, it’s important to note that the conditional part of the for loop can only contain one boolean expression.
Syntax
for (initial1, initial2; condition; update1, update2) {
// Code block to be executed
}
package ch5;
public class MultipleStatementLoop {
public static void main(String[] args) {
for (int i = 0, j = 10; i < j; i++, j--) {
System.out.println("i = " + i + ", j = " + j);
}
}
}
Output
i = 0, j = 10
i = 1, j = 9
i = 2, j = 8
i = 3, j = 7
i = 4, j = 6
In this example, i is initialized to 0 and j to 10. The loop runs until i is less than j. In each iteration, i is incremented and j is decremented.
package ch5;
public class SumAndAverage {
public static void main(String[] args) {
int sum = 0, count = 0;
for (int i = 1, j = 10; i <= j; i++, j--, count++) {
sum += i + j;
}
double average = (double) sum / count;
System.out.println("Sum: " + sum + ", Average: " + average);
}
}
Output
Sum: 55, Average: 11.0
Here, the loop calculates the sum of the numbers from 1 to 10 and their reverse (10 to 1) in each iteration. It also counts the number of iterations to calculate the average.
A nested for loop in Java refers to a for loop within another for loop.
Note: Nested for loop allows you to perform complex iterations, and it’s commonly used in scenarios where you need to work with multi-dimensional data structures like arrays.
package ch5;
public class NestedLoop {
public static void main(String[] args) {
for (int i = 1; i <= 10; i++) { // Outer loop
for (int j = 1; j <= 10; j++) { // Inner loop
System.out.print(i * j + "t"); // Print the product
}
System.out.println(); // New line after each row
}
}
}
Output
1 2 3 4 5 6 7 8 9 10
2 4 6 8 10 12 14 16 18 20
3 6 9 12 15 18 21 24 27 30
4 8 12 16 20 24 28 32 36 40
5 10 15 20 25 30 35 40 45 50
6 12 18 24 30 36 42 48 54 60
7 14 21 28 35 42 49 56 63 70
8 16 24 32 40 48 56 64 72 80
9 18 27 36 45 54 63 72 81 90
10 20 30 40 50 60 70 80 90 100
This code prints a 10×10 multiplication table.
package ch5;
public class CreatingPatternForLoop {
public static void main(String[] args) {
int rows = 5;
for (int i = 1; i <= rows; i++) { // Outer loop for rows
for (int j = 1; j <= i; j++) { // Inner loop for columns
System.out.print("* "); // Print a star
}
System.out.println(); // New line after each row
}
}
}
Output
*
* *
* * *
* * * *
* * * * *
This code will print a left-aligned pyramid of stars with 5 rows.
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