for Loop in Java With Examples

Loop in any programming language is used to repeatedly execute a block of code until a condition to terminate the loop is satisfied. In Java there are three types of loops- while loop, do-while loop and for loop. In this post we’ll see how to use for loop in Java.

Java for loop

In Java there are two forms of for loop.

  1. Traditional for loop
  2. Enhanced for loop (for-each loop)

Syntax of the traditional for loop is as follows-

Block of code that is executed with in a loop is enclosed with in curly braces. If there is only one statement that has to be executed with in a for loop then curly braces are optional.

Java for loop execution flow

Following image shows the execution flow of the for loop.
for loop in Java
1. Initialization– When the execution of the for loop starts, first step is initialization which is executed only once in the beginning. Initialization step is generally used to set the initial value of the variable which controls the for loop. This variable is later incremented or decremented in the increment\decrement step of the loop.

2. Condition– Condition is a boolean expression that is evaluated in each iteration. If condition is true then the loop body is executed, if condition is false then the loop terminates.

3. Increment\decrement– In this step the variable that controls the loop is incremented or decremented.

Java for loop examples

1- First example uses for loop to print numbers from 1 to 10.

Output

1- First the variable is declared and initialized to 1.

2- Condition (i <= 10) is evaluated in each iteration, it returns true till value of i is less than 10. Condition is evaluated to false when value of i becomes 10 and the loop terminates.

3- Third part of the for loop increments the control variable.

In the next iteration of the for loop only step-2 and step-3 are executed as initialization happens only once.

You can see in the code that the variable declaration and initialization (int i = 0) both happened with in the for loop. Declared like this the scope of the variable is limited with in the loop.

2- Second example uses for loop to print numbers in reverse order 10 to 1.

Output

3- In the third example numbers 1 to 20 are added.

Output

You can see that the curly braces are not used here as curly braces are optional when there is a single statement with in the for loop.

4- Till now all the examples have used all the three parts of the for loop with in the loop statement but for loop is flexible about the initialization and increment/decrement part.

Output

In the code both initialization and increment/decrement part are moved out of the loop statement. Note that you still need to have semicolons for those.

For-each loop (Enhanced for loop) in Java

Java 5 onward there is another version of for loop available known as for-each loop or enhanced for loop.
Enhanced for loop is used to iterate a collection of objects like an array, list or set sequentially.

Syntax of the for-each loop is as follows-

Here type specifies the type of the elements in the collection.

var is the variable that is assigned the next element from the collection in each iteration.

collection specifies the collection that is iterated.

Java for-each loop examples

1- Iterating an array using for-each and getting the sum of all the elements in the array.

Output

In the code, in each iteration of the for-each loop num variable is assigned the next element of the array nums.

2- Iterating an ArrayList of Strings and displaying values.

Output

Nested for loop

In Java, like in most of the programming languages, for loop can be nested. So, you can have one for loop inside another. In the nested loops for each iteration of the outer for loop, inner for loop is iterated until the condition in the inner for loop is not satisfied.

For example following program prints the pyramid pattern using nested for loops.

Output

That’s all for the topic for Loop in Java With Examples. If something is missing or you have something to share about the topic please write a comment.


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