How to store an array of pairs in Java?

Question

I am new to Java, I want to store an array of pair of doubles. My code looks like this:

import java.util.ArrayList;
import java.util.Map.Entry;

List

        

Answer 1

Another approach, and probably the most efficient way to store and array of double pairs is to use a single array of doubles, and use (2*i) and (2*i + 1) as your indexing scheme. Additionally you gain the advantage that the array will be initialized to all 0s when you create it, no additional steps required. Unfortunately there is a little extra coding overhead to implement add() and remove(), but surprisingly, it's probably less than creating your own container class for the pair.

class MyClass {
    double[] values;
    int count;

    MyClass(int initialCapacity) {
        values = new double[initialCapacity*2];
    }

    // adding a pair
    void addPair(double x, double y) {
        if (count*2 >= values.length) {
            values = Arrays.copyOf(values, values.length*2);
        }
        values[count*2] = x;
        values[count*2 + 1] = y;
        count++;
    }

    void remove(int index) {
        if (index >= count) throw new IndexOutOfBoundsException();

        if (index < --count) {
            System.arraycopy(values, (index+1)*2, values, index*2, (count - index) * 2);
        }
    }

    int size() { return count; }

    // both these should check that index < count.
    double getX(int index) { return values[index*2]; }
    double getY(int index) { return values[index*2 + 1]; }

    void exampleIteration() {
        // getX/Y accessors are examples of how to get
        // the values, but it will be more efficient
        // in most cases to just access the array
        // array directly as so...
        for (int i=0 ; i