How to Convert `int[]` to `Integer[]` in Java for Use in a Map

How can I convert `int[]` to `Integer[]` in Java?

int[] primitiveArray = {1, 2, 3}; 
Integer[] objectArray = Arrays.stream(primitiveArray)
                              .boxed()
                              .toArray(Integer[]::new);

In Java, there's a difference between primitive arrays and their wrapper counterparts, which can cause issues when working with collections like `Map`. This guide will show you how to convert an `int[]` to an `Integer[]`, allowing you to store the arrays in a `Map` object.

Map<Integer[], Double> frequencies = new HashMap<>();

for (int[] q : data) {
    Integer[] qInteger = Arrays.stream(q)
                                .boxed()
                                .toArray(Integer[]::new);
                                
    frequencies.put(qInteger, frequencies.getOrDefault(qInteger, 0.0) + p);
}

Causes

• Java distinguishes between primitive types (`int`, `double`, etc.) and their wrapped object types (`Integer`, `Double`, etc.). This means collections like `Map` cannot accept primitive types directly.
• `int[]` is considered a primitive array, while `Integer[]` is an object array, resulting in type mismatch errors.

Solutions

• Use the `java.util.Arrays` utility class to convert an `int[]` to an `Integer[]`. This can be done using the `boxed` method from Java Streams.
• Example code: ```java int[] primitiveArray = {1, 2, 3}; Integer[] objectArray = Arrays.stream(primitiveArray) .boxed() .toArray(Integer[]::new); ```
• Now you can use this `Integer[]` in your `Map`.

Mistake: Attempting to use `int[]` directly in a `Map<Integer[], Double>` without conversion.

Solution: Use the conversion method shown to properly transform `int[]` to `Integer[]`.

Mistake: Not accounting for the possibility of duplicate arrays being treated as different keys in the Map.

Solution: Consider using a custom key class which overrides `equals()` and `hashCode()` methods to manage `int[]` equality.