Java TreeMap pollLastEntry() Method

The TreeMap.pollLastEntry() method in Java is used to retrieve and remove the last (highest) key-value pair from a TreeMap. This guide will cover the method’s usage, explain how it works, and provide examples to demonstrate its functionality. We will also cover a real-world use case to show how TreeMap.pollLastEntry() can be used effectively.

Table of Contents

1. Introduction
2. pollLastEntry Method Syntax
3. Examples
   • Removing the Last Entry from a TreeMap
   • Handling an Empty TreeMap
4. Real-World Use Case
   • Example: Managing a Priority Queue of Tasks
5. Conclusion

Introduction

The TreeMap.pollLastEntry() method is a member of the TreeMap class in Java. It retrieves and removes the last (highest) key-value pair from the TreeMap. If the map is empty, it returns null. This method is useful when you need to process and remove the highest entry from a sorted map.

pollLastEntry() Method Syntax

The syntax for the pollLastEntry method is as follows:

public Map.Entry<K,V> pollLastEntry()

• The method does not take any parameters.
• The method returns a Map.Entry<K,V> representing the last (highest) key-value pair, or null if the map is empty.

Examples

Removing the Last Entry from a TreeMap

The pollLastEntry method can be used to remove the last key-value pair from a TreeMap.

Example

import java.util.TreeMap;
import java.util.Map;

public class PollLastEntryExample {
    public static void main(String[] args) {
        // Creating a TreeMap with String keys and Integer values
        TreeMap<String, Integer> treeMap = new TreeMap<>();

        // Adding entries to the TreeMap
        treeMap.put("Ravi", 25);
        treeMap.put("Priya", 30);
        treeMap.put("Vijay", 35);
        treeMap.put("Anita", 28);
        treeMap.put("Suresh", 40);

        // Removing the last entry from the TreeMap
        Map.Entry<String, Integer> lastEntry = treeMap.pollLastEntry();

        // Printing the removed entry
        System.out.println("Removed last entry: " + lastEntry);

        // Printing the TreeMap after removal
        System.out.println("TreeMap after removing last entry: " + treeMap);
    }
}

Output:

Removed last entry: Suresh=40
TreeMap after removing last entry: {Anita=28, Priya=30, Ravi=25, Vijay=35}

Handling an Empty TreeMap

The pollLastEntry method returns null if the TreeMap is empty.

Example

import java.util.TreeMap;
import java.util.Map;

public class EmptyTreeMapExample {
    public static void main(String[] args) {
        // Creating an empty TreeMap
        TreeMap<String, Integer> treeMap = new TreeMap<>();

        // Attempting to remove the last entry from an empty TreeMap
        Map.Entry<String, Integer> lastEntry = treeMap.pollLastEntry();

        // Printing the result
        System.out.println("Removed last entry from empty TreeMap: " + lastEntry);
    }
}

Output:

Removed last entry from empty TreeMap: null

Real-World Use Case

Example: Managing a Priority Queue of Tasks

A common real-world use case for TreeMap.pollLastEntry() is managing a priority queue of tasks where the highest priority task is processed and removed.

Example

import java.util.TreeMap;
import java.util.Map;

public class TaskManager {
    public static void main(String[] args) {
        // Creating a TreeMap to manage tasks with priorities
        TreeMap<Integer, String> taskQueue = new TreeMap<>();

        // Adding tasks to the TreeMap with their priorities
        taskQueue.put(1, "Complete report");
        taskQueue.put(3, "Schedule meeting");
        taskQueue.put(2, "Review code");
        taskQueue.put(5, "Fix bugs");
        taskQueue.put(4, "Update documentation");

        // Processing and removing the highest priority task
        Map.Entry<Integer, String> highestPriorityTask = taskQueue.pollLastEntry();

        // Printing the highest priority task
        System.out.println("Processed highest priority task: " + highestPriorityTask);

        // Printing the remaining tasks
        System.out.println("Remaining tasks: " + taskQueue);
    }
}

Output:

Processed highest priority task: 5=Fix bugs
Remaining tasks: {1=Complete report, 2=Review code, 3=Schedule meeting, 4=Update documentation}

In this example, TreeMap.pollLastEntry() is used to process and remove the highest priority task from a priority queue, making it easy to manage and update the task list.

Conclusion

The TreeMap.pollLastEntry() method in Java provides a way to retrieve and remove the last (highest) key-value pair from a TreeMap. By understanding how to use this method, you can efficiently manage collections of key-value pairs in your Java applications. The method allows you to process and remove the highest entries, making it a versatile tool for data management in various scenarios.