Loops in Java: Repeat your code multiple times


Keywords: loops, iterations sets, conditional loops, counting loops, while loop, for loop, do-while loop

Loops Java Programming

This chapter will look at loops in Java which is a way to repeat an operation an arbitrary number of times. We will see that there are different types of loops that you can use and we will, of course, go through how they are used and when it is best to use the different types of loops.

Loops in Java

When programming, it is prevalent that you want to repeat parts of your code several times. To do this we use loops, also called iteration sets. Loops are beneficial when programming if you’re going to reuse a certain code sequence several times. In this chapter, we will see the three iteration sets, the while loop, the for loop, and the do-while loop

More specifically, we will go through which loop is beneficial to use depending on whether you want to operate a specific number of times, or if you want to repeat an operation until a particular condition is met. This chapter contains the following articles where we will learn what it means with the different loops with a series of examples for each loop. 

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What is a loop?

When you want to repeat an operation or a code sequence several times, you should use a loop. The loop is used to repeat a statement or block of statements as long as a particular condition is true. The term “control flow statement” is often used to refer to loops in Java programming generally. There are usually two different types of loops, namely the conditional loop or the counting loop, that is used. 

Java provides three repetition statements/looping statements that enable programmers to control the flow of execution by repetitively performing a set of statements as long as the continuation condition remains true

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How to use loops in Java?

Loops are one of the most basic and useful parts of basically all programming languages. A loop repeats a code sequence until a specified state is reached. The loop checks if a condition is met, and repeats the loop as long as the condition is met. The same process is repeated over and over until the condition is no longer met, and then the program continues.

Let us illustrate a loop using the flow chart below

Loops Java Programming

Figure 1: Loop in Java

Let’s have a look what happens in Figure 1

  1. The code sequence begins at Start and then checks if the loop conditions are met.
  2. If the condition is met, true, the program performs the operation, if the condition is not met, the program proceeds.
  3. The loop then repeats the process and goes back and examines if the condition is met.

What is a conditional loop in Java?

We use the condition loop when we want to repeat a code sequence, over and over again, until a specified condition is fulfilled. This means that the code block is executed as long as a condition is met and the loop will after each execution of the code block go back and evaluate if the condition is met. The condition loops that we will take a closer look at in this chapter are the while loop and the do-while loop.

Example of conditional loops in Java

There are countless uses for conditional loops in Java programming, but if we are going to take some, that will give you an idea of how it can be used. For example, you have programmed a program to run as long as the user does not give the exit command. Thus, there will be a condition that as long as input from the user is not “quit”, the loop will run. 

Furthermore, another example of uses could be that you want to go through a list or collection of data until you find a particular keyword. If you have a large amount of data and are looking for one, or more, elements, you can use a condition loop until you find the right element. Your condition will then be that as long as you have not found what you are looking for, the loop should check the next place in the data list.

What is a counting loop in Java?

The counting loop repeats a code sequence a predetermined number of times. Therefore, we use the counting loop when we want to repeat an operation a specific number of times. You often want to run a code block several times in a row. The counting loop that we are going to look at in this chapter is the for loop.

Example of counting loop in Java

We use counting loops when the number of iterations is fixed. Therefore, we usually use counting loops to go through lists or a predetermined number of iterations. For example, a list of participants and based on information, a command must be executed. It may be a teacher who has a list of his students who continuously updates their grades based on a number of different tests. Instead of having the teacher go through the list manually, the counting loop can do so and then collect and modify the information. 

In general, when it comes to counting loops, it is possible to iterate from the beginning to the end, or vice versa. You can also modify the loop so that you take every other step, or maybe every third step. As you realize, it is possible to adjust the calculation loop to several different purposes.

Infinity loops in Java

So-called infinity loops are loops that never gets terminated. The condition of the loop is never met, therefore, the loop continues forever. An infinity loop can be due to several reasons; for example, that you forget to update the variables that are in the loop. However,  your compiler will end the loop. Thus, it will also cause your program to shut down, and you will receive an error message

Summary: Loops in Java

Loops in Java is used to repeat a statement or block of statements as long as a particular condition is true. We use loops as a command that iterates part of the program several times. Furthermore, we use two different types of loops, the conditional loop that runs until a specified condition is fulfilled, and the count loop that repeats a code sequence a predetermined number of times. The three loops in Java are While loop, For loop and Do-while loop.

FAQ: Loops in Java

What is the condition loop and count loop?

The conditional loop runs the code block until a specified condition is fulfilled, and the count loop executes the code sequence a predetermined number of times. Therefore, you could say that the count loop is a conditional loop, since the predetermined number of times is a condition.

Which are the loops used in Java?

The three most common loops in Java are: While loop, For loop and Do-while loop.

What is an infinity loop and how do you avoid them?

An infinity loop is a loop that does not proceed in the program and thus gets stuck inside the loop without being able to move on. The infinity loop can be due to several reasons. However, usually, you forget to initiate or update the variables that are inside the loop that enables the loop to end.