How to Create a List<Double> That Uses the Memory of a double[] Array in Java?

How can I create a List<Double> in Java that shares the same memory as a double[] array?

// The code snippet for creating a List<Double> from a double[] array is shown below:
double[] array = {1.0, 2.0, 3.0};
List<Double> list = new AbstractList<Double>() {
    @Override
    public Double get(int index) {
        return array[index];
    }

    @Override
    public int size() {
        return array.length;
    }
};

In Java, while the standard List implementation (like ArrayList) does not directly share memory with an array, you can create a custom implementation of a List that leverages a double[] array for memory efficiency. This is particularly useful in scenarios where you want to work with primitives but need the flexibility of a List interface.

// Custom List implementation sample
double[] array = {1.0, 2.0, 3.0};
List<Double> list = new AbstractList<Double>() {
    @Override
    public Double get(int index) {
        return array[index];  // Retrieve from double[]
    }
    @Override
    public int size() {
        return array.length;  // Return size from double[]
    }
};

Causes

• Java's List interface does not directly support primitive types, necessitating boxing and unboxing with Double and List<Double>.
• Memory overhead from creating a new List implementation, as it would typically create objects for each element.

Solutions

• Implement a custom List that extends AbstractList and overrides the necessary methods to delegate to the underlying double[] array.
• Use a library such as Eclipse Collections or Apache Commons that provides specialized collections for primitive types.

Mistake: Not handling index out-of-bounds for the List implementation.

Solution: Always ensure to check the index within the bounds of the double[] array.

Mistake: Boxing and unboxing can lead to performance degradation.

Solution: Use a custom implementation that avoids boxing whenever possible.