Infinite Loop in Java

Introduction

All the loops such as while, for, and do-while loops have one thing in common: the condition. Loops are executed till the condition evaluates to true. In this blog, we will discuss the scenario where the condition always evaluates to true i.e. the condition never fails.

• This will lead to an infinite loop that will keep on executing unless the application is closed or the system crashes.
• Most of the time infinite loops are created as a programming error but in some cases, infinite loops are created intentionally for some code to execute periodically.
• These loops are terminated only on the termination of the application or if the system crashes.

Let's see how infinite loops in Java are implemented using while, for, and do-while loops.

Using While Loop

Syntax of While Loop

The code part inside the body of while loop is executed if the condition is true else the while loop is terminated. So we have to provide a condition that will always evaluate to true and this can be achieved by passing true itself as the condition in the above loop.

Code:

Output:

Explanation:

If we try to run the above code, the code will print Hello World as the while loop keeps on executing for infinite time.

IMPORTANT: If there is a time limit on the period of execution, TimeLimitExceeded error will be thrown.

Using For Loop

Syntax of for loop

Let's have a brief recap of for loop in Java, the initialization expression is used to initialize the counter, and the condition expression tests whether we have to execute the body of the for loop or we have to terminate the loop. The updation expression is executed after each execution of the for loop.

Let's have an example of for loop in Java,

Output:

Explanation:

• In the initialization part, the variable i is assigned the value $0$, and if i is less than $3$ the body of the for loop is executed.
• After each execution of the for loop, i is incremented by $1$. After executing the for loop for $i=2$, i becomes $3$, and the condition $i<3$ evaluates to false thus resulting in the termination of the for loop.

So in the case of for loop in Java, we can also pass the condition expression as true so that the for loop executes for infinite time.

Output:

Explanation:

• In the code above, the body of the loop is executed till i is less than 3.
• However, instead of incrementing the value of i, we are decreasing it in the updation statement.
• As a result, the condition is always true and the loop executes infinitely.

But here is a twist, in the case of for loop the expressions initialization, condition, and updation are optional whereas in the case of the while loop the condition expression was mandatory. So if we leave this expression as empty, the above for loop will execute for infinite time.

Output:

Using a do-While Loop

Syntax of do-while loop

The do-while loop in Java is similar to the while loop in Java, but with one minor change. The do-while loop executes the do block of the loop and then checks the condition. So the do-while loop is executed atleast once even if the condition is false.

Let's have an example of this:

Output:

And just like the while loop, the condition expression is mandatory.

Like we did in the while loop, we will pass true as the condition and the above loop will execute for infinite time.

Output:

Now we have learned the infinite loops in Java, let's move on to the intentional infinite loops in Java.

Intentional Infinite Loops

Sometimes we intentionally want an infinite loop for example in a web server. A typical web server accepts a request for a web page, such as a communicative message, and returns a web page while waiting for the next request.

Thus the web server needs to be active always to read and process upcoming requests. This can be achieved by using infinite loops as,

or,