From 432679d8fccadbf6a41f505ba9f63b3c377e66ba Mon Sep 17 00:00:00 2001 From: Priyesh Date: Tue, 29 Jul 2025 02:47:58 +0530 Subject: [PATCH 1/3] [Term Entry] Java Queue: isEmpty() --- .../concepts/queue/terms/isEmpty/isEmpty.md | 249 ++++++++++++++++++ 1 file changed, 249 insertions(+) create mode 100644 content/java/concepts/queue/terms/isEmpty/isEmpty.md diff --git a/content/java/concepts/queue/terms/isEmpty/isEmpty.md b/content/java/concepts/queue/terms/isEmpty/isEmpty.md new file mode 100644 index 00000000000..f533a9d46ff --- /dev/null +++ b/content/java/concepts/queue/terms/isEmpty/isEmpty.md @@ -0,0 +1,249 @@ +--- +Title: '.isEmpty()' +Description: 'Returns true if the queue contains no elements, false otherwise.' +Subjects: + - 'Code Foundations' + - 'Computer Science' +Tags: + - 'Collections' + - 'Queues' + - 'Data Structures' + - 'Methods' +CatalogContent: + - 'learn-java' + - 'paths/computer-science' +--- + +The **`.isEmpty()`** method is a built-in method of the [ Queue ](https://www.codecademy.com/resources/docs/java/queue) interface in Java that returns `true` if the queue contains no elements, and `false` otherwise. This method is inherited from the `Collection` interface and provides a convenient way to check if a queue is empty before performing operations that require elements. The method has O(1) time complexity in most implementations, making it an efficient way to validate queue state. + +## Syntax + +```pseudo +queue.isEmpty() +``` + +**Parameters:** + +- None + +**Return value:** + +The `.isEmpty()` method returns a `boolean` value: +- `true` if the queue contains no elements +- `false` if the queue contains one or more elements + +## When to Use `.isEmpty()` + +The `.isEmpty()` method is particularly useful in the following scenarios: + +1. **Before polling elements**: To avoid `null` returns or exceptions +2. **In loop conditions**: To process all elements safely +3. **Validation checks**: Before performing operations that require elements +4. **Algorithm implementations**: In data structure algorithms and queue-based solutions + +## Example 1: Basic Usage of `.isEmpty()` + +In this example, `.isEmpty()` is used to check if a queue is empty before and after adding elements: + +```java +import java.util.LinkedList; +import java.util.Queue; + +public class Main { + public static void main(String[] args) { + Queue queue = new LinkedList(); + + // Check if queue is empty initially + System.out.println("Is queue empty? " + queue.isEmpty()); + System.out.println("Queue contents: " + queue); + + // Add elements to the queue + queue.offer("First"); + queue.offer("Second"); + queue.offer("Third"); + + // Check if queue is empty after adding elements + System.out.println("Is queue empty after adding elements? " + queue.isEmpty()); + System.out.println("Queue contents: " + queue); + System.out.println("Queue size: " + queue.size()); + + // Remove all elements + queue.poll(); + queue.poll(); + queue.poll(); + + // Check if queue is empty after removing all elements + System.out.println("Is queue empty after removing all elements? " + queue.isEmpty()); + System.out.println("Queue contents: " + queue); + } +} +``` + +The output of this code is: + +```shell +Is queue empty? true +Queue contents: [] +Is queue empty after adding elements? false +Queue contents: [First, Second, Third] +Queue size: 3 +Is queue empty after removing all elements? true +Queue contents: [] +``` + +## Example 2: Using `.isEmpty()` in a Loop + +This example demonstrates how `.isEmpty()` can be used to safely process all elements in a queue: + +```java +import java.util.LinkedList; +import java.util.Queue; + +public class Main { + public static void main(String[] args) { + Queue numbers = new LinkedList(); + + // Add some numbers to the queue + numbers.offer(10); + numbers.offer(20); + numbers.offer(30); + numbers.offer(40); + numbers.offer(50); + + System.out.println("Initial queue: " + numbers); + System.out.println("Processing all elements in the queue:"); + + int elementCount = 0; + // Process all elements until queue is empty + while (!numbers.isEmpty()) { + Integer number = numbers.poll(); + elementCount++; + System.out.println("Processing element #" + elementCount + ": " + number); + System.out.println("Remaining elements: " + numbers.size()); + } + + System.out.println("Queue is now empty: " + numbers.isEmpty()); + System.out.println("Total elements processed: " + elementCount); + } +} +``` + +The output of this code is: + +```shell +Initial queue: [10, 20, 30, 40, 50] +Processing all elements in the queue: +Processing element #1: 10 +Remaining elements: 4 +Processing element #2: 20 +Remaining elements: 3 +Processing element #3: 30 +Remaining elements: 2 +Processing element #4: 40 +Remaining elements: 1 +Processing element #5: 50 +Remaining elements: 0 +Queue is now empty: true +Total elements processed: 5 +``` + + + +## Codebyte Example + +Here's a runnable example showing advanced usage of `.isEmpty()` with error handling: + +```codebyte/java +import java.util.LinkedList; +import java.util.Queue; + +public class Main { + public static void main(String[] args) { + Queue taskQueue = new LinkedList(); + + // Method to safely add tasks + addTask(taskQueue, "Initialize system"); + addTask(taskQueue, "Load configuration"); + addTask(taskQueue, "Start services"); + + // Process all tasks + processAllTasks(taskQueue); + + // Try to process empty queue + processAllTasks(taskQueue); + } + + public static void addTask(Queue queue, String task) { + queue.offer(task); + System.out.println("Added task: " + task); + System.out.println("Queue empty: " + queue.isEmpty() + ", Size: " + queue.size()); + } + + public static void processAllTasks(Queue queue) { + if (queue.isEmpty()) { + System.out.println("No tasks to process"); + return; + } + + System.out.println("\nProcessing tasks:"); + int taskNumber = 1; + while (!queue.isEmpty()) { + String task = queue.poll(); + System.out.println("Task " + taskNumber + ": " + task); + taskNumber++; + } + System.out.println("All tasks completed. Queue empty: " + queue.isEmpty()); + } +} +``` + +## Performance Considerations + +- **Time Complexity**: O(1) - constant time for most queue implementations +- **Space Complexity**: O(1) - no additional space required +- **Thread Safety**: The `.isEmpty()` method itself is typically not synchronized. For thread-safe operations, consider using `ConcurrentLinkedQueue` or synchronize access manually + +## Best Practices + +1. **Always check before polling**: Use `.isEmpty()` before calling `.poll()` to avoid getting `null` values +2. **Prefer over size comparison**: Use `.isEmpty()` instead of `.size() == 0` for better readability +3. **Combine with other checks**: Use `.isEmpty()` in conjunction with other validation methods +4. **Loop conditions**: Use `!queue.isEmpty()` as loop conditions for processing all elements + +## Frequently Asked Questions + +### 1. What's the difference between `.isEmpty()` and checking `.size() == 0`? + +Both `.isEmpty()` and `.size() == 0` will give the same result, but `.isEmpty()` is generally preferred because: +- It's more readable and expresses intent clearly +- Some implementations might optimize `.isEmpty()` to be faster than calculating the size +- It follows Java naming conventions for boolean methods + +### 2. Can `.isEmpty()` be used with all Queue implementations? + +Yes, `.isEmpty()` is available for all classes that implement the `Queue` interface, including: +- `LinkedList` +- `ArrayDeque` +- `PriorityQueue` +- `ConcurrentLinkedQueue` +- And any custom implementations + +### 3. Is it safe to call `.isEmpty()` on a null queue? + +No, calling `.isEmpty()` on a `null` reference will throw a `NullPointerException`. Always ensure your queue is properly initialized: + +```java +Queue queue = null; +// This will throw NullPointerException +// boolean empty = queue.isEmpty(); + +// Safe approach +if (queue != null && !queue.isEmpty()) { + // Process queue +} +``` + +### 4. Does `.isEmpty()` modify the queue? + +No, `.isEmpty()` is a read-only operation that doesn't modify the queue's contents or structure. It only returns information about the current state. + From 6d69b66bb1855db424dbd79cc67f3984d8a1b07d Mon Sep 17 00:00:00 2001 From: Priyesh Date: Tue, 29 Jul 2025 03:01:09 +0530 Subject: [PATCH 2/3] [Term Entry] Java Queue: isEmpty() #7369 --- .../concepts/queue/terms/isEmpty/isEmpty.md | 38 +++++++++---------- 1 file changed, 19 insertions(+), 19 deletions(-) diff --git a/content/java/concepts/queue/terms/isEmpty/isEmpty.md b/content/java/concepts/queue/terms/isEmpty/isEmpty.md index f533a9d46ff..b1973b4b913 100644 --- a/content/java/concepts/queue/terms/isEmpty/isEmpty.md +++ b/content/java/concepts/queue/terms/isEmpty/isEmpty.md @@ -14,7 +14,7 @@ CatalogContent: - 'paths/computer-science' --- -The **`.isEmpty()`** method is a built-in method of the [ Queue ](https://www.codecademy.com/resources/docs/java/queue) interface in Java that returns `true` if the queue contains no elements, and `false` otherwise. This method is inherited from the `Collection` interface and provides a convenient way to check if a queue is empty before performing operations that require elements. The method has O(1) time complexity in most implementations, making it an efficient way to validate queue state. +The **`.isEmpty()`** method is a built-in method of the [Queue](https://www.codecademy.com/resources/docs/java/queue) interface in Java that returns `true` if the queue contains no elements, and `false` otherwise. This method is inherited from the `Collection` interface and provides a convenient way to check if a queue is empty before performing operations that require elements. The method has O(1) time complexity in most implementations, making it an efficient way to validate queue state. ## Syntax @@ -29,6 +29,7 @@ queue.isEmpty() **Return value:** The `.isEmpty()` method returns a `boolean` value: + - `true` if the queue contains no elements - `false` if the queue contains one or more elements @@ -52,26 +53,26 @@ import java.util.Queue; public class Main { public static void main(String[] args) { Queue queue = new LinkedList(); - + // Check if queue is empty initially System.out.println("Is queue empty? " + queue.isEmpty()); System.out.println("Queue contents: " + queue); - + // Add elements to the queue queue.offer("First"); queue.offer("Second"); queue.offer("Third"); - + // Check if queue is empty after adding elements System.out.println("Is queue empty after adding elements? " + queue.isEmpty()); System.out.println("Queue contents: " + queue); System.out.println("Queue size: " + queue.size()); - + // Remove all elements queue.poll(); queue.poll(); queue.poll(); - + // Check if queue is empty after removing all elements System.out.println("Is queue empty after removing all elements? " + queue.isEmpty()); System.out.println("Queue contents: " + queue); @@ -102,17 +103,17 @@ import java.util.Queue; public class Main { public static void main(String[] args) { Queue numbers = new LinkedList(); - + // Add some numbers to the queue numbers.offer(10); numbers.offer(20); numbers.offer(30); numbers.offer(40); numbers.offer(50); - + System.out.println("Initial queue: " + numbers); System.out.println("Processing all elements in the queue:"); - + int elementCount = 0; // Process all elements until queue is empty while (!numbers.isEmpty()) { @@ -121,7 +122,7 @@ public class Main { System.out.println("Processing element #" + elementCount + ": " + number); System.out.println("Remaining elements: " + numbers.size()); } - + System.out.println("Queue is now empty: " + numbers.isEmpty()); System.out.println("Total elements processed: " + elementCount); } @@ -147,8 +148,6 @@ Queue is now empty: true Total elements processed: 5 ``` - - ## Codebyte Example Here's a runnable example showing advanced usage of `.isEmpty()` with error handling: @@ -160,31 +159,31 @@ import java.util.Queue; public class Main { public static void main(String[] args) { Queue taskQueue = new LinkedList(); - + // Method to safely add tasks addTask(taskQueue, "Initialize system"); addTask(taskQueue, "Load configuration"); addTask(taskQueue, "Start services"); - + // Process all tasks processAllTasks(taskQueue); - + // Try to process empty queue processAllTasks(taskQueue); } - + public static void addTask(Queue queue, String task) { queue.offer(task); System.out.println("Added task: " + task); System.out.println("Queue empty: " + queue.isEmpty() + ", Size: " + queue.size()); } - + public static void processAllTasks(Queue queue) { if (queue.isEmpty()) { System.out.println("No tasks to process"); return; } - + System.out.println("\nProcessing tasks:"); int taskNumber = 1; while (!queue.isEmpty()) { @@ -215,6 +214,7 @@ public class Main { ### 1. What's the difference between `.isEmpty()` and checking `.size() == 0`? Both `.isEmpty()` and `.size() == 0` will give the same result, but `.isEmpty()` is generally preferred because: + - It's more readable and expresses intent clearly - Some implementations might optimize `.isEmpty()` to be faster than calculating the size - It follows Java naming conventions for boolean methods @@ -222,6 +222,7 @@ Both `.isEmpty()` and `.size() == 0` will give the same result, but `.isEmpty()` ### 2. Can `.isEmpty()` be used with all Queue implementations? Yes, `.isEmpty()` is available for all classes that implement the `Queue` interface, including: + - `LinkedList` - `ArrayDeque` - `PriorityQueue` @@ -246,4 +247,3 @@ if (queue != null && !queue.isEmpty()) { ### 4. Does `.isEmpty()` modify the queue? No, `.isEmpty()` is a read-only operation that doesn't modify the queue's contents or structure. It only returns information about the current state. - From c0c8f0082e2a8eb36006eaf4f807f8b22dbf0cc0 Mon Sep 17 00:00:00 2001 From: Mamta Wardhani Date: Sat, 2 Aug 2025 12:44:55 +0530 Subject: [PATCH 3/3] minor content fixes --- .../concepts/queue/terms/isEmpty/isEmpty.md | 110 +----------------- 1 file changed, 5 insertions(+), 105 deletions(-) diff --git a/content/java/concepts/queue/terms/isEmpty/isEmpty.md b/content/java/concepts/queue/terms/isEmpty/isEmpty.md index b1973b4b913..48a475efb46 100644 --- a/content/java/concepts/queue/terms/isEmpty/isEmpty.md +++ b/content/java/concepts/queue/terms/isEmpty/isEmpty.md @@ -6,25 +6,25 @@ Subjects: - 'Computer Science' Tags: - 'Collections' - - 'Queues' - 'Data Structures' - 'Methods' + - 'Queues' CatalogContent: - 'learn-java' - 'paths/computer-science' --- -The **`.isEmpty()`** method is a built-in method of the [Queue](https://www.codecademy.com/resources/docs/java/queue) interface in Java that returns `true` if the queue contains no elements, and `false` otherwise. This method is inherited from the `Collection` interface and provides a convenient way to check if a queue is empty before performing operations that require elements. The method has O(1) time complexity in most implementations, making it an efficient way to validate queue state. +The **`.isEmpty()`** method is a built-in method of the [`Queue`](https://www.codecademy.com/resources/docs/java/queue) interface in Java that returns `true` if the queue contains no elements, and `false` otherwise. This method is inherited from the [`Collection`](https://www.codecademy.com/resources/docs/java/collection) interface and provides a convenient way to check if a queue is empty before performing operations that require elements. The method has O(1) time complexity in most implementations, making it an efficient way to validate queue state. ## Syntax ```pseudo -queue.isEmpty() +queueName.isEmpty() ``` **Parameters:** -- None +- The `.isEmpty()` method does not take any parameters. **Return value:** @@ -42,7 +42,7 @@ The `.isEmpty()` method is particularly useful in the following scenarios: 3. **Validation checks**: Before performing operations that require elements 4. **Algorithm implementations**: In data structure algorithms and queue-based solutions -## Example 1: Basic Usage of `.isEmpty()` +## Example 1: Basic Usage of `.isEmpty()` Method In this example, `.isEmpty()` is used to check if a queue is empty before and after adding elements: @@ -147,103 +147,3 @@ Remaining elements: 0 Queue is now empty: true Total elements processed: 5 ``` - -## Codebyte Example - -Here's a runnable example showing advanced usage of `.isEmpty()` with error handling: - -```codebyte/java -import java.util.LinkedList; -import java.util.Queue; - -public class Main { - public static void main(String[] args) { - Queue taskQueue = new LinkedList(); - - // Method to safely add tasks - addTask(taskQueue, "Initialize system"); - addTask(taskQueue, "Load configuration"); - addTask(taskQueue, "Start services"); - - // Process all tasks - processAllTasks(taskQueue); - - // Try to process empty queue - processAllTasks(taskQueue); - } - - public static void addTask(Queue queue, String task) { - queue.offer(task); - System.out.println("Added task: " + task); - System.out.println("Queue empty: " + queue.isEmpty() + ", Size: " + queue.size()); - } - - public static void processAllTasks(Queue queue) { - if (queue.isEmpty()) { - System.out.println("No tasks to process"); - return; - } - - System.out.println("\nProcessing tasks:"); - int taskNumber = 1; - while (!queue.isEmpty()) { - String task = queue.poll(); - System.out.println("Task " + taskNumber + ": " + task); - taskNumber++; - } - System.out.println("All tasks completed. Queue empty: " + queue.isEmpty()); - } -} -``` - -## Performance Considerations - -- **Time Complexity**: O(1) - constant time for most queue implementations -- **Space Complexity**: O(1) - no additional space required -- **Thread Safety**: The `.isEmpty()` method itself is typically not synchronized. For thread-safe operations, consider using `ConcurrentLinkedQueue` or synchronize access manually - -## Best Practices - -1. **Always check before polling**: Use `.isEmpty()` before calling `.poll()` to avoid getting `null` values -2. **Prefer over size comparison**: Use `.isEmpty()` instead of `.size() == 0` for better readability -3. **Combine with other checks**: Use `.isEmpty()` in conjunction with other validation methods -4. **Loop conditions**: Use `!queue.isEmpty()` as loop conditions for processing all elements - -## Frequently Asked Questions - -### 1. What's the difference between `.isEmpty()` and checking `.size() == 0`? - -Both `.isEmpty()` and `.size() == 0` will give the same result, but `.isEmpty()` is generally preferred because: - -- It's more readable and expresses intent clearly -- Some implementations might optimize `.isEmpty()` to be faster than calculating the size -- It follows Java naming conventions for boolean methods - -### 2. Can `.isEmpty()` be used with all Queue implementations? - -Yes, `.isEmpty()` is available for all classes that implement the `Queue` interface, including: - -- `LinkedList` -- `ArrayDeque` -- `PriorityQueue` -- `ConcurrentLinkedQueue` -- And any custom implementations - -### 3. Is it safe to call `.isEmpty()` on a null queue? - -No, calling `.isEmpty()` on a `null` reference will throw a `NullPointerException`. Always ensure your queue is properly initialized: - -```java -Queue queue = null; -// This will throw NullPointerException -// boolean empty = queue.isEmpty(); - -// Safe approach -if (queue != null && !queue.isEmpty()) { - // Process queue -} -``` - -### 4. Does `.isEmpty()` modify the queue? - -No, `.isEmpty()` is a read-only operation that doesn't modify the queue's contents or structure. It only returns information about the current state.