Java PriorityQueue clear() Method

In Java, the PriorityQueue class provides the clear() method to remove all elements from the queue.

Table of Contents

1. Introduction
2. clear Method Syntax
3. Examples
   • Clearing Elements from a PriorityQueue
   • Handling an Already Empty PriorityQueue
4. Real-World Use Case
   • Use Case: Task Management System
5. Conclusion

Introduction

The PriorityQueue.clear() method is used to remove all elements from the PriorityQueue. This method is useful when you need to reset the queue, ensuring that it is empty and ready for new elements.

clear Method Syntax

The syntax for the clear method is as follows:

public void clear()

• The method does not take any parameters.
• The method does not return any value.

Examples

Clearing Elements from a PriorityQueue

The clear method can be used to remove all elements from a PriorityQueue.

Example

import java.util.PriorityQueue;

public class PriorityQueueClearExample {
    public static void main(String[] args) {
        // Creating a PriorityQueue of Strings
        PriorityQueue<String> tasks = new PriorityQueue<>();

        // Adding elements to the PriorityQueue
        tasks.add("Complete project report");
        tasks.add("Email client updates");
        tasks.add("Prepare presentation");

        // Printing the PriorityQueue before clearing
        System.out.println("PriorityQueue before clear: " + tasks);

        // Clearing the PriorityQueue
        tasks.clear();

        // Printing the PriorityQueue after clearing
        System.out.println("PriorityQueue after clear: " + tasks);
    }
}

Output:

PriorityQueue before clear: [Complete project report, Email client updates, Prepare presentation]
PriorityQueue after clear: []

Handling an Already Empty PriorityQueue

When the PriorityQueue is already empty, calling clear will simply leave the queue empty without any exceptions.

Example

import java.util.PriorityQueue;

public class EmptyPriorityQueueClearExample {
    public static void main(String[] args) {
        // Creating an empty PriorityQueue of Strings
        PriorityQueue<String> tasks = new PriorityQueue<>();

        // Printing the PriorityQueue before clearing
        System.out.println("PriorityQueue before clear: " + tasks);

        // Clearing the PriorityQueue
        tasks.clear();

        // Printing the PriorityQueue after clearing
        System.out.println("PriorityQueue after clear: " + tasks);
    }
}

Output:

PriorityQueue before clear: []
PriorityQueue after clear: []

Real-World Use Case

Use Case: Task Management System

In a task management system, there may be scenarios where you need to clear all tasks from the queue, such as when resetting the system or starting a new project cycle. The clear method can be used to achieve this functionality.

Example

import java.util.PriorityQueue;

public class TaskManagementSystem {
    public static void main(String[] args) {
        // Creating a PriorityQueue to store tasks
        PriorityQueue<Task> tasks = new PriorityQueue<>();

        // Adding initial tasks with different priorities
        tasks.add(new Task("Complete project report", 2));
        tasks.add(new Task("Email client updates", 1));
        tasks.add(new Task("Prepare presentation", 3));

        // Printing the tasks before clearing
        System.out.println("Tasks before clear: " + tasks);

        // Clearing the tasks
        tasks.clear();

        // Printing the tasks after clearing
        System.out.println("Tasks after clear: " + tasks);
    }
}

class Task implements Comparable<Task> {
    private String description;
    private int priority;

    public Task(String description, int priority) {
        this.description = description;
        this.priority = priority;
    }

    @Override
    public int compareTo(Task other) {
        return Integer.compare(this.priority, other.priority);
    }

    @Override
    public String toString() {
        return description + " (Priority: " + priority + ")";
    }
}

Output:

Tasks before clear: [Email client updates (Priority: 1), Complete project report (Priority: 2), Prepare presentation (Priority: 3)]
Tasks after clear: []

Conclusion

By using PriorityQueue.clear() method, you can easily reset the queue, removing all elements and preparing it for new or elements. This method is particularly useful in applications like task management systems, where you may need to clear and restart the task queue periodically.