Pair Class in Java

In Java, a Pair class is often used to represent a simple container for two objects (often referred to as a “tuple” in other languages). The Pair class is not a built-in part of Java’s standard library (prior to Java 8), but it can be easily implemented.

You might also come across Pair in various Java libraries, such as Apache Commons Lang, which has a Pair class.

Here’s an example of a simple Pair class in Java:

Custom Pair Class:

public class Pair<T, U> {
    private T first;
    private U second;

    // Constructor to initialize the Pair
    public Pair(T first, U second) {
        this.first = first;
        this.second = second;
    }

    // Getter for the first element
    public T getFirst() {
        return first;
    }

    // Getter for the second element
    public U getSecond() {
        return second;
    }

    // Setter for the first element
    public void setFirst(T first) {
        this.first = first;
    }

    // Setter for the second element
    public void setSecond(U second) {
        this.second = second;
    }

    // Override toString for better readability
    @Override
    public String toString() {
        return "(" + first + ", " + second + ")";
    }

    // Override equals and hashCode if necessary (for comparing pairs)
    @Override
    public boolean equals(Object obj) {
        if (this == obj) return true;
        if (obj == null || getClass() != obj.getClass()) return false;
        Pair<?, ?> pair = (Pair<?, ?>) obj;
        return first.equals(pair.first) && second.equals(pair.second);
    }

    @Override
    public int hashCode() {
        return 31 * first.hashCode() + second.hashCode();
    }
}

Usage of the Pair class:

public class Main {
    public static void main(String[] args) {
        // Creating a pair of Integer and String
        Pair<Integer, String> pair = new Pair<>(1, "Java");

        // Accessing the elements of the pair
        System.out.println("First: " + pair.getFirst());
        System.out.println("Second: " + pair.getSecond());

        // Modifying the elements
        pair.setFirst(2);
        pair.setSecond("Python");

        System.out.println("Updated Pair: " + pair);
    }
}

Output:

First: 1
Second: Java
Updated Pair: (2, Python)

Java Libraries with Pair:

If you want to avoid writing your own Pair class, libraries like Apache Commons Lang and JavaFX provide implementations:

• Apache Commons Lang: org.apache.commons.lang3.tuple.Pair
• JavaFX: javafx.util.Pair

For example, using Apache Commons Lang’s Pair:

import org.apache.commons.lang3.tuple.Pair;

public class Main {
    public static void main(String[] args) {
        Pair<Integer, String> pair = Pair.of(1, "Java");

        System.out.println("First: " + pair.getLeft());
        System.out.println("Second: " + pair.getRight());
    }
}