在 Java 中实现一对 class 的最佳方法

Question

I have written the following code for a Pair class in Java using Map.Entry. Does anyone have any recommendations for improving it? The most important criteria for me that the class needed to meet were that it would be easy to construct a Pair and that.equals would work the way I wanted it to (equality of the two objects in the Pair in the same order means equality of the Pairs). The code seems to function as intended and is not used in anything that is taxing my system's memory yet, but any optimizations would be appreciated.

import java.util.*;

public class Pair {
    // Return a map entry (key-value pair) from the specified values
    public static <T, U> Map.Entry<T, U> of(T first, U second) {
        return new AbstractMap.SimpleEntry<>(first, second);
    }

    private Map.Entry entry;

    public Pair (Object x, Object y) {
        Set<Map.Entry> entries = new HashSet<>();
        entries.add(Pair.of(x, y));
        Object[] setArray = entries.toArray();
        this.entry = (Map.Entry) setArray[0];
    }

    public Object getKey() {
        return entry.getKey();
    }
    public Object getValue() {
        return entry.getValue();
    }


    @Override
    public boolean equals(Object o)
    {
        if (o instanceof Pair) {
            Pair pair = (Pair) o;
            return ( (entry.getKey().equals(pair.getKey())) && (entry.getValue().equals(pair.getValue())) );
        }
        return false;
    }

    @Override
    public int hashCode() {
            return Objects.hash(entry.getKey(), entry.getValue());
    }

    @Override
    public String toString() {
            return String.format( "(" +entry.getKey().toString() + ", " + entry.getValue().toString() + ")" );
    }
}

I have been considering using Collections.singletonMap instead of Map.Entry.

So far, I have successfully tested my code using the following:

import java.util.HashMap;

public class Main {

    public static void main(String[] args) {
        HashMap<Pair, Integer> testMap = new HashMap<>();
        Pair onThrup = new Pair(1, 3);
        System.out.println(onThrup); //Prints contents of Pair, not hash
        testMap.put(onThrup, 7);
        Pair unoTres = new Pair(1, 3);
        System.out.println(onThrup.equals(unoTres));
        System.out.println(testMap.containsKey(onThrup));
        System.out.println(unoTres.hashCode() == onThrup.hashCode());
        System.out.println(testMap.containsKey(unoTres)); // Should be, and is, true
    }
}

Answer 1

Java 16 includes Record Classes :

public record Pair<K, V>(K key, V value) {
    // intentionally empty
}

Creates a class with final fields, methods to retrieve key and value , equals , hashCode and toString methods.

Usage example:

var one = new Pair<Integer, String>(1, "one");
var two = new Pair(2, "two");
System.out.println(one);   // Pair[key=1, value=one]
if (!one.equals(two))
    System.out.printf("not same as Pair for %d%n", two.key());

^{not sure what is best, if available (java 16) I would use that}

JLS 8.10
JEP 395