How to convert int[] to Integer[] in Java?

I'm new to Java and very confused.

I have a large dataset of length 4 int[] and I want to count the number of times that each particular combination of 4 integers occurs. This is very similar to counting word frequencies in a document.

I want to create a Map<int[], double> that maps each int[] to a running count as the list is iterated over, but Map doesn't take primitive types.

so I made Map<Integer[], Double>

my data is stored as an ArrayList<int[]> so my loop should be something like

ArrayList<int[]> data = ... // load a dataset`

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

for(int[] q : data) {

    // **DO SOMETHING TO convert q from int[] to Integer[] so I can put it in the map

    if(frequencies.containsKey(q)) {
    frequencies.put(q, tfs.get(q) + p);
    } else {
        frequencies.put(q, p);
    }
}

I'm not sure what code I need at the comment to make this work to convert an int[] to an Integer[]. Or maybe I'm fundamentally confused about the right way to do this.

Solution 1:

Native Java 8 (one line)

With Java 8, int[] can be converted to Integer[] easily:

int[] data = {1,2,3,4,5,6,7,8,9,10};

// To boxed array
Integer[] what = Arrays.stream( data ).boxed().toArray( Integer[]::new );
Integer[] ever = IntStream.of( data ).boxed().toArray( Integer[]::new );

// To boxed list
List<Integer> you  = Arrays.stream( data ).boxed().collect( Collectors.toList() );
List<Integer> like = IntStream.of( data ).boxed().collect( Collectors.toList() );

As others stated, Integer[] is usually not a good map key. But as far as conversion goes, we now have a relatively clean and native code.

Solution 2:

If you want to convert an int[] to an Integer[], there isn't an automated way to do it in the JDK. However, you can do something like this:

int[] oldArray;

... // Here you would assign and fill oldArray

Integer[] newArray = new Integer[oldArray.length];
int i = 0;
for (int value : oldArray) {
    newArray[i++] = Integer.valueOf(value);
}

If you have access to the Apache lang library, then you can use the ArrayUtils.toObject(int[]) method like this:

Integer[] newArray = ArrayUtils.toObject(oldArray);