1. What are the different types of loops in Java?
There are four primary types of loops used for iteration:
1. For Loop
Used when the number of iterations is known. It runs for a specified number of times, with initialization, condition, and increment/decrement.
2. While Loop
Runs as long as the condition is true, with the condition checked before each iteration. It’s used when the number of iterations is unknown.
3.Do-While Loop
Similar to the while loop but guarantees at least one iteration, as the condition is checked after the loop runs. It’s useful when you need to execute the loop at least once.Top of Form
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4. For Each Loop
The for-each loop is a control structure in Java used to traverse through each element of an array or collection directly, without using an index variable.
2. Explain the syntax of a for loop in Java. How does it work?
Syntax :
for (initialization; condition; increment/decrement) {
// code to be executed
}
Initialization: Initializes the loop variable (executed once at the start).
Condition: A boolean expression that is checked before each iteration. The loop continues if it’s true.
Increment/Decrement: Updates the loop variable after each iteration.
How it works:
- Initialization – Runs once at the beginning (e.g., int i = 0).
- Condition – Checked before each iteration. If true, the loop continues.
- Update – Executes after each iteration (e.g., i++).
3. Explain the syntax of a while loop in java?
The syntax of a while loop in Java is:
while (condition) {
// code to be executed
}
- The condition is checked before each iteration.
- If the condition is true, the loop body runs.
- This repeats until the condition becomes false.
4. Explain the syntax of a do-while loop in java?
The syntax of a do-while loop in Java is:
do {
// code to be executed
} while (condition);
- The code inside the loop is executed at least once, regardless of the condition.
- The condition is checked after the loop executes, and if true, the loop continues.
5. What is the difference between while and do-while loops in Java?
while loop:
- Checks the condition before executing the loop body.
- The loop may not run at all if the condition is false.
do-while loop:
- Executes the loop body at least once, then checks the condition.
- The loop runs at least once, even if the condition is false initially.
6. When would you use a for loop instead of a while loop and vice versa?
- Use a for loop when the number of iterations is known or controlled by a counter (e.g., looping 10 times, iterating through arrays).
- Use a while loop when the number of iterations is unknown and depends on a condition that may change during execution (e.g., reading input until a condition is met).
7. How do you break out of a loop in Java?
You can use the break statement to exit a loop immediately, even if the loop condition is still true.
Example:
| for (int i = 0; i < 10; i++) { if (i == 5) { break; // Exits the loop when i equals 5 } System.out.println(i); } Output: 1 2 3 4 |
8. What does the continue statement do in a loop? Provide an example?
The continue statement skips the current iteration of a loop and moves to the next iteration.
Example:
| for (int i = 1; i <= 5; i++) { if (i == 3) { continue; // Skips the iteration when i is 3 } System.out.println(i); } |
9. How does a for-each loop work in Java? Provide an example?
A for-each loop in Java is used to iterate over elements in an array or a collection, without the need for an index. It simplifies the code and provides a clean way to access each element.
Syntax:
for (type variable : collection) {
// body of the loop
}
Example:
| int[] numbers = {1, 2, 3, 4, 5}; for (int num : numbers) { System.out.println(num); } |
Output:
| 1 2 3 4 5 |
10. Can you have an infinite loop in java? If yes, explain how?
Yes, an infinite loop in Java is possible. It happens when the loop is designed so that its condition never becomes false or the termination condition is omitted entirely, causing the loop to run endlessly.
Example:
| while loop: while (true) { System.out.println(“This is an infinite loop”); } |
11. What happens if you have a continue statement inside a nested loop? How does it behave?
When a continue statement is inside a nested loop, it only affects the innermost loop. It skips the current iteration of that loop and moves to the next iteration of the inner loop, not the outer loop.
Example:
| for (int i = 1; i <= 3; i++) { for (int j = 1; j <= 3; j++) { if (j == 2) { continue; // Skips when j is 2, only affects the inner loop } System.out.println(“i: ” + i + “, j: ” + j); } } |
12. How can you exit from multiple nested loops in Java?
To exit from multiple nested loops in Java, you can use a labeled break statement. By labeling the outer loop, you can break out of it directly from within the inner loop.
Example:
| outerLoop: for (int i = 1; i <= 3; i++) { for (int j = 1; j <= 3; j++) { if (j == 2) { break outerLoop; // Exits both loops when j equals 2 } System.out.println(“i: ” + i + “, j: ” + j); } } |
13. How can you skip an iteration of an outer loop when the inner loop completes in Java?
To skip an iteration of an outer loop when the inner loop completes in Java, you can use a continuestatement in conjunction with a labeled continue for the outer loop.
Example:
| outerLoop: for (int i = 1; i <= 3; i++) { for (int j = 1; j <= 3; j++) { if (j == 2) { continue outerLoop; // Skips the current iteration of the outer loop } System.out.println(“i: ” + i + “, j: ” + j); } } |
14. How do you exit a loop prematurely without using break?
You can exit a loop prematurely without using break by modifying the loop’s condition so that it becomes false. This can be done by using a flag variable or by directly changing the loop control variable.
15. What is the difference between the for loop and for each loop?
The for loop and for-each loop are both used for iteration, but they differ in how they work:
- For loop:
- Uses an index or counter.
- Offers more control (e.g., access to index, custom step size).
- Syntax: for (int i = 0; i < arr.length; i++)
- For-each loop:
- Iterates directly over elements in a collection or array.
- Simpler and cleaner when you don’t need the index.
- Syntax: for (int item : arr)
Main difference:
- Use for loop when you need the index or want custom iteration.
- Use for-each loop for simpler, direct element access.
