Java For loop, Examples, Nested For Loop

For Loop in Java:

In java, for loop has two versions.

1) Basic for loop (Old style)
2) Enhanced for loop (For-each or for-in loop)

First, we will discuss about basic for loop then next discuss about Enhanced loop.
Enhanced loop is designed mainly for Arrays or Collection. We will discuss in next tutorial.

Enhanced for loop and Examples.

Basic for loop:

Basic loop has flexibility to use it as per our needs. This is very useful if we know how many times it needs to be executed.

It has three sections.

1) Variable declaration and its initialization
2) Condition: Untill condition is true, loop will be executed.
3) Variable increment/decrement

Syntax:

for(declaration ; condition ; increment/decrement)
{
    // some repetited code here
}

All these three are separated by semicolon (;).

Rules:

1) Declarations can be multiple and are separated by comma(,).
2) Condition should be only one. This can be logical expression or function which returns boolean.
3) multiple Increment/Decrement statements are allowed and separated by comma(,).
4) All these sections are optional but there should be semicolons.
5) Variables declared inside for loop are not accessible outside its loop. Scope is only limited to for loop.
6) All variables must be same data type.

For loop execution:

First initializes the variables
Second checks the condition. if condition is true then executes the statements inside loop.
Third increemnt or decreemnt variable
Then repeats the second and third points untill condition is false.

For loop Examples:

package com.java.s3schools.switchdemo;
public class ForLoopExample {
    public static void main(String[] args) {
        for (int i = 1; i <= 10; i++) {
            System.out.println("i value : " + i);
        }
    }
}

Output:

i value : 1
i value : 2
i value : 3
i value : 4
i value : 5
i value : 6
i value : 7
i value : 8
i value : 9
i value : 10

More about:

If , If-else, nested if else condition in java

While loop in java, Examples

Switch Statement in java

Inner For loop or Nested loop example:

package com.java.s3schools.switchdemo;

public class InnerForLoopExample {
    public static void main(String[] args) {
        for (int i = 1; i <= 3; i++) {
            for (int j = 1; j <= 5; j++) {
                System.out.println("i value :: " + i + ", j value :: " + j);
            }
            System.out.println("-----------------------------");
        }
    }
}

Output:

i value :: 1, j value :: 1
i value :: 1, j value :: 2
i value :: 1, j value :: 3
i value :: 1, j value :: 4
i value :: 1, j value :: 5
-----------------------------
i value :: 2, j value :: 1
i value :: 2, j value :: 2
i value :: 2, j value :: 3
i value :: 2, j value :: 4
i value :: 2, j value :: 5
-----------------------------
i value :: 3, j value :: 1
i value :: 3, j value :: 2
i value :: 3, j value :: 3
i value :: 3, j value :: 4
i value :: 3, j value :: 5
-----------------------------

Draw backs of For loop:

The following are drawbacks for basic for loop which makes the code less readable and all are legal to use.

1) As mentioned varaible declaration, condition, increment variable are optional. If we remove these three then loop becomes infinate loop.

for ( ; ; )
{
    System.out.println("inside loop")
}

2) If variable initialization is done outside for loop then it looks like while loop.

int i=0;

for ( ; i <= 10 ;)
{
    i++;
    // code here
}

3) In increment/decrement section, we can write any code as following.

int i=1;

for( ; i < 3; System.out.println("loop...."))
{
    i++;
}

Output:

loop....
loop....

All these drawbacks are fixed by enhanced for loop.

Next, will see For each loop in java, Enhanced loop in java, Enhanced loop Example.