Java For Loops Explained with Examples

Guide
1

For Loop

The for loop gives you a compact way to iterate over a range of values. A basic for statement has three parts: a variable initialization, a boolean expression, and an increment expression.

for (variable initialization; boolean expression; increment expression)
{  
    // Statements
}
  • initialization - Initializes the loop and is executed just once, at the beginning.

You can initialize more than one variable of the same type in the first part of the basic for loop declaration; each initialization must be separated by a comma. Remember that the variable(s) declared as the initialization will only be used within that for loop and nowhere else outside of the loop.

  • expression - Evaluated at the beginning of each iteration. If the expression evaluates to true , Statements will get executed.
  • increment - Invoked after each iteration through the loop. You can increase/decrease the value of variables here. Be sure the increment is working towards the expression value, to avoid an infinite loop.

A common way the for loop is used is if you need to iterate your code a specific number of times. For example, if you wanted to output the numbers 0-10, you would initialize the variable for your counter to 0, then check if the value is less than 10, and add one to the counter after every iteration.

Notice that you would check if the value is less than 10, not less than or equal to 10, since you are starting your counter at 0.

for (int iter_For = 0; iter_For < 10; iter_For++)
{
    System.out.print(iter_For + " ");
    // Iterated 10 times, iter_For 0,1,2...9
}

Note: It is also acceptable to declare a variable within the for loop as a single statement.

for (int iter_For = 0; iter_For < 10; iter_For++)
{
    System.out.print (iter_For + " ");
    // Iterated 10 times, iter_For 0,1,2...9
}

Output:

0 1 2 3 4 5 6 7 8 9
iter_For Value: 10

Another example of a for loop that adds the first 50 numbers would be like this. i++ means i = i+1.

int addUntil = 50;
int sum 0;

for (int i = 1; i <= addUntil; i++) 
{
    sum+=i
}

System.out.println("The sum of the first 50 numbers is: " + sum);

:rocket: Run Code

Extras

One thing to keep in mind is that for is also an entry controlled loop just like while loop, where condition is checked at the beginning. So, do keep that in mind before writing the starting condition of the loop.

You cannot use a number (old C-style language construct) or anything that does not evaluate to a boolean value as a condition for an if statement or looping construct. You can’t, for example, say if(x), unless x is a boolean variable.

Also, it is important to keep in mind that the boolean expression must, at some point, evaluate to true. Otherwise, your program will be stuck in an infinite loop.