for Loop

Loops in any programming language are used to execute a block of code again and again until a base condition is achieved. As soon as a base condition is satisfied the loop is terminated and the control is returned to the main body of the program.

There are three types of loops in java:

• for loop
• while loop
• do……while loop

 

for loop:

Whenever a loop needs to be run a specific number of times, we use a for loop.

Syntax:

for (initializeVariable, testCondition, increment/decrement){
//block of code
}

• initializeVariable: initialize a new variable or use an already existing one.
• testCondition: It checks the testing condition of the loop after each iteration and returns a Boolean value, which determines if the loop should be terminated or not.
• Increment/decrement: It is used to increment or decrement the variable after each iteraton.

 

Example:

public class ForLoop1 {
    public static void main(String[] args) {
        for(int i=1; i<=10; i++) {
            System.out.println("2 * "+ i+ " = "+ 2*i);
        }
    }
}

Output:

2 * 1 = 2
2 * 2 = 4
2 * 3 = 6
2 * 4 = 8
2 * 5 = 10
2 * 6 = 12
2 * 7 = 14
2 * 8 = 16
2 * 9 = 18
2 * 10 = 20

 

We also have a special syntax for iterating through arrays and other collection objects, also called as a for-each loop.

Syntax:

for (type variable : collectionObject){
    //block of code
}

 

Example:

public class ForEach1 {
    public static void main(String[] args) {
        int[] prime = {1,3,5,7,11,13,17,19};
        System.out.println("Prime numbers are:");
        for(int i : prime) {
            System.out.println(i);
        }
    }
}

Output:

Prime numbers are:
1
3
5
7
11
13
17
19

 

And lastly we have an infinite for loop, wherein the expression always evaluates to true, hence running indefinitely.

Example:

public class ForLoop1 {
    public static void main(String[] args) {
        for(int i=1; i<=10; i--) {
            System.out.println(i);
        }
    }
}

 

Output:

-3832975
-3832976
-3832977
-3832978
-3832979
-3832980
-3832981
-3832982
-3832983
-3832984
-3832985
.
.
.
.

The loop will keep on running until you halt the program.