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AP Computer Science A

•

Dec 7, 2025

•

29 pages

Mastering Loops in Java Programming

Samantha Montez

@samanthamontez_kjgf

Loops are essential programming structures that let you repeat code... Show more

1 / 10

Loops: While and Do-While

Loops are programming structures that help you execute the same code multiple times. Instead of writing the same lines of code over and over, loops let your program repeat actions automatically.

Think of loops like putting your music player on repeat - the same song plays again and again until you tell it to stop.

In this section, we'll explore the two main types of loops: while loops and do-while loops, which are essential tools for any programmer.

Fundamentals of Looping: Iteration

When you use a loop, each complete run through the loop is called an iteration. Think of it as one complete cycle through the loop.

For example, if you want to print numbers from 1 to 10, your loop will go through 10 iterations - once for each number you need to print. The loop repeats the print instruction 10 separate times, rather than you having to write 10 separate lines of code.

💡 Iterations are like laps around a track - each time you complete the full circuit, that's one iteration!

Fundamentals of Looping: Accumulator

An accumulator is a special variable that collects or builds up a value during a loop. It's like a running total that changes with each iteration.

For example, instead of just printing numbers 1 through 10, you might want to calculate their sum (1+2+3...+10). The accumulator stores this running total as your loop progresses.

Think of an accumulator like a snowball rolling down a hill - it gets bigger as it picks up more snow along the way.

Example: Summing Numbers

Let's say we want to find the sum of numbers from 1 to 10. The final answer should be 55 (1+2+3+4+5+6+7+8+9+10).

To solve this with a loop, we need to add each number as we go through the sequence. Our loop will run 10 times (10 iterations), adding each number to our running total.

This is much more efficient than writing out the entire calculation by hand, especially if we needed to sum hundreds or thousands of numbers!

💡 This pattern of accumulating values is super common in programming - you'll use it for everything from calculating averages to building strings!

Using an Accumulator in Practice

When calculating a sum, our accumulator starts at zero and grows with each loop iteration. As the loop counts from 1 to 10, we add each number to our accumulator.

For example:

Start with sum = 0
First iteration: sum becomes 0+1 = 1
Second iteration: sum becomes 1+2 = 3
Third iteration: sum becomes 3+3 = 6
And so on until we reach 55

Accumulators aren't just for addition! They can be used for multiplication (like calculating factorials) or even building strings character by character.

Counter Variables

A counter is a variable that keeps track of how many iterations your loop has completed. It's like the lap counter at a race track.

Counters typically start at a specific value (like 0 or 1) and increase or decrease with each loop iteration. They serve two important purposes:

They track how many times the loop has run
They often provide values for your calculations inside the loop

For example, if you're adding numbers 1-10, your counter might start at 1 and increase until it reaches 10, with each value being added to your accumulator along the way.

💡 Counter variables are often named with single letters like i, j, or k by convention, though descriptive names like "count" work too!

Types of Loops: Infinite Loop

An infinite loop is a loop that never ends - it just keeps running forever. This usually happens because of a mistake in your code.

Infinite loops occur when the condition that's supposed to eventually stop the loop never becomes false. For example:

while (true) {
    System.out.println("This will never end!");
}

These loops can crash your program or make it unresponsive. If you accidentally create one while coding, you'll usually need to force-quit your program.

💡 Be careful with your loop conditions! Always make sure there's a way for your loop to eventually end.

Types of Loops: Pre-Condition Loops

Pre-condition loops like WHILE and FOR check whether they should run before executing any code. They follow this pattern:

Check if the condition is true
If true, run the loop body
Go back to step 1
If false, skip the loop entirely

This means a while loop might execute zero times if the condition is false from the start.

while (condition) {
    // Loop body - only runs if condition is true
}

Pre-condition loops are great when you might not need to run the loop at all depending on the initial conditions.

Types of Loops: Post-Condition Loops

A post-condition loop (like DO-WHILE) runs its code block first, then checks the condition to see if it should run again. This guarantees the loop body runs at least once.

do {
    // Loop body - always runs at least once
} while (condition);

The key difference from pre-condition loops is timing - do-while executes its code first, then checks if it should continue.

This type of loop is perfect when you need to ensure your code runs at least once, like when validating user input or processing at least one item in a collection.

💡 Remember: while loops might run zero times, but do-while loops always run at least once!

Implementing Loops in Programs

Now that we understand the theory behind loops, let's see how to implement them in actual programs.

In programming languages like Java, loops have specific syntax and rules. We'll focus on the practical aspects of creating while and do-while loops in code.

The examples that follow will demonstrate how to translate loop concepts into working programs that solve real problems. Pay close attention to how we set up the loop conditions and how we modify our counter variables within the loops.

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iOS user

Samantha Klich

Android user

Anna

iOS user

Thomas R

iOS user

Brad T

Android user

Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍

David K

iOS user

Sudenaz Ocak

Android user

In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.

Greenlight Bonnie

Android user

Aubrey

iOS user

Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀

Marco B

iOS user

Elisha

iOS user

Paul T

iOS user

Subjects

AP Computer Science A

•

Dec 7, 2025

•

29 pages

Mastering Loops in Java Programming

Samantha Montez

@samanthamontez_kjgf

Loops are essential programming structures that let you repeat code sections without writing them multiple times. They save time and make your code more efficient by automating repetitive tasks through different types of structures like while and do-while loops.

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Loops: While and Do-While

Loops are programming structures that help you execute the same code multiple times. Instead of writing the same lines of code over and over, loops let your program repeat actions automatically.

Think of loops like putting your music player on repeat - the same song plays again and again until you tell it to stop.

In this section, we'll explore the two main types of loops: while loops and do-while loops, which are essential tools for any programmer.

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Fundamentals of Looping: Iteration

When you use a loop, each complete run through the loop is called an iteration. Think of it as one complete cycle through the loop.

💡 Iterations are like laps around a track - each time you complete the full circuit, that's one iteration!

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Fundamentals of Looping: Accumulator

An accumulator is a special variable that collects or builds up a value during a loop. It's like a running total that changes with each iteration.

For example, instead of just printing numbers 1 through 10, you might want to calculate their sum (1+2+3...+10). The accumulator stores this running total as your loop progresses.

Think of an accumulator like a snowball rolling down a hill - it gets bigger as it picks up more snow along the way.

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Example: Summing Numbers

Let's say we want to find the sum of numbers from 1 to 10. The final answer should be 55 (1+2+3+4+5+6+7+8+9+10).

To solve this with a loop, we need to add each number as we go through the sequence. Our loop will run 10 times (10 iterations), adding each number to our running total.

This is much more efficient than writing out the entire calculation by hand, especially if we needed to sum hundreds or thousands of numbers!

💡 This pattern of accumulating values is super common in programming - you'll use it for everything from calculating averages to building strings!

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Using an Accumulator in Practice

When calculating a sum, our accumulator starts at zero and grows with each loop iteration. As the loop counts from 1 to 10, we add each number to our accumulator.

For example:

Start with sum = 0
First iteration: sum becomes 0+1 = 1
Second iteration: sum becomes 1+2 = 3
Third iteration: sum becomes 3+3 = 6
And so on until we reach 55

Accumulators aren't just for addition! They can be used for multiplication (like calculating factorials) or even building strings character by character.

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Counter Variables

A counter is a variable that keeps track of how many iterations your loop has completed. It's like the lap counter at a race track.

Counters typically start at a specific value (like 0 or 1) and increase or decrease with each loop iteration. They serve two important purposes:

They track how many times the loop has run
They often provide values for your calculations inside the loop

For example, if you're adding numbers 1-10, your counter might start at 1 and increase until it reaches 10, with each value being added to your accumulator along the way.

💡 Counter variables are often named with single letters like i, j, or k by convention, though descriptive names like "count" work too!

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Types of Loops: Infinite Loop

An infinite loop is a loop that never ends - it just keeps running forever. This usually happens because of a mistake in your code.

Infinite loops occur when the condition that's supposed to eventually stop the loop never becomes false. For example:

while (true) {
    System.out.println("This will never end!");
}

These loops can crash your program or make it unresponsive. If you accidentally create one while coding, you'll usually need to force-quit your program.

💡 Be careful with your loop conditions! Always make sure there's a way for your loop to eventually end.

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Types of Loops: Pre-Condition Loops

Pre-condition loops like WHILE and FOR check whether they should run before executing any code. They follow this pattern:

Check if the condition is true
If true, run the loop body
Go back to step 1
If false, skip the loop entirely

This means a while loop might execute zero times if the condition is false from the start.

while (condition) {
    // Loop body - only runs if condition is true
}

Pre-condition loops are great when you might not need to run the loop at all depending on the initial conditions.

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Types of Loops: Post-Condition Loops

A post-condition loop (like DO-WHILE) runs its code block first, then checks the condition to see if it should run again. This guarantees the loop body runs at least once.

do {
    // Loop body - always runs at least once
} while (condition);

The key difference from pre-condition loops is timing - do-while executes its code first, then checks if it should continue.

This type of loop is perfect when you need to ensure your code runs at least once, like when validating user input or processing at least one item in a collection.

💡 Remember: while loops might run zero times, but do-while loops always run at least once!

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Implementing Loops in Programs

Now that we understand the theory behind loops, let's see how to implement them in actual programs.

In programming languages like Java, loops have specific syntax and rules. We'll focus on the practical aspects of creating while and do-while loops in code.

We thought you’d never ask...

What is the Knowunity AI companion?

Where can I download the Knowunity app?

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Is Knowunity really free of charge?

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Stefan S

iOS user

Samantha Klich

Android user

Anna

iOS user

Thomas R

iOS user

Brad T

Android user

Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍

David K

iOS user

Sudenaz Ocak

Android user

In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.

Greenlight Bonnie

Android user

Aubrey

iOS user

Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀

Marco B

iOS user

Elisha

iOS user

Paul T

iOS user

Stefan S

iOS user

Samantha Klich

Android user

Anna

iOS user

Thomas R

iOS user

Brad T

Android user

Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍

David K

iOS user

Sudenaz Ocak

Android user

In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.

Greenlight Bonnie

Android user

Aubrey

iOS user

Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀

Marco B

iOS user

Elisha

iOS user

Paul T

iOS user

Mastering Loops in Java Programming

Loops: While and Do-While

Fundamentals of Looping: Iteration

Fundamentals of Looping: Accumulator

Example: Summing Numbers

Using an Accumulator in Practice

Counter Variables

Types of Loops: Infinite Loop

Types of Loops: Pre-Condition Loops

Types of Loops: Post-Condition Loops

Implementing Loops in Programs

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Loops: While and Do-While

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Fundamentals of Looping: Iteration

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Fundamentals of Looping: Accumulator

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Example: Summing Numbers

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Using an Accumulator in Practice

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Implementing Loops in Programs

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Most popular content: Loop

Loop statements java programming

Loops on Java Programming

Most popular content in AP Computer Science A

python

HTML tags, codes, definition

AP CSP Notes

Understanding Data Types in Python

Entrepreneurship

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FAR NOTES- CPM

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