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

Question

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.

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);

Convert int[] to Integer[]:

    import java.util.Arrays;
    ...

    int[] aint = {1,2,3,4,5,6,7,8,9,10};
    Integer[] aInt = new Integer[aint.length];

    Arrays.setAll(aInt, i -> aint[i]);

Using regular for-loop without external libraries:

Convert int[] to Integer[]:

int[] primitiveArray = {1, 2, 3, 4, 5};
Integer[] objectArray = new Integer[primitiveArray.length];

for(int ctr = 0; ctr < primitiveArray.length; ctr++) {
    objectArray[ctr] = Integer.valueOf(primitiveArray[ctr]); // returns Integer value
}

Convert Integer[] to int[]:

Integer[] objectArray = {1, 2, 3, 4, 5};
int[] primitiveArray = new int[objectArray.length];

for(int ctr = 0; ctr < objectArray.length; ctr++) {
    primitiveArray[ctr] = objectArray[ctr].intValue(); // returns int value
}

Presumably you want the key to the map to match on the value of the elements instead of the identity of the array. In that case you want some kind of object that defines equals and hashCode as you would expect. Easiest is to convert to a List<Integer>, either an ArrayList or better use Arrays.asList. Better than that you can introduce a class that represents the data (similar to java.awt.Rectangle but I recommend making the variables private final, and the class final too).

1. Convert int[] to Integer[]

   public static Integer[] toConvertInteger(int[] ids) {
   
     Integer[] newArray = new Integer[ids.length];
        for (int i = 0; i < ids.length; i++) {
          newArray[i] = Integer.valueOf(ids[i]);
        }
      return newArray;
   }
   

2. Convert Integer[] to int[]

   public static int[] toint(Integer[] WrapperArray) {
   
      int[] newArray = new int[WrapperArray.length];
         for (int i = 0; i < WrapperArray.length; i++) {
            newArray[i] = WrapperArray[i].intValue();
         }
      return newArray;
   }
   

I was wrong in a previous answer. The proper solution is to use this class as a key in the map wrapping the actual int[].

public class IntArrayWrapper {
        int[] data;

        public IntArrayWrapper(int[] data) {
            this.data = data;
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) return true;
            if (o == null || getClass() != o.getClass()) return false;

            IntArrayWrapper that = (IntArrayWrapper) o;

            if (!Arrays.equals(data, that.data)) return false;

            return true;
        }

        @Override
        public int hashCode() {
            return data != null ? Arrays.hashCode(data) : 0;
        }
    }

and change your code like this:

   Map<IntArrayWrapper, Double > freqs = new HashMap<IntArrayWrapper, Double>();

    for (int[] data : datas) {
        IntArrayWrapper wrapper = new IntArrayWrapper(data);

        if ( freqs.containsKey(wrapper)) {
            freqs.put(wrapper, freqs.get(wrapper) + p);
        }

        freqs.put(wrapper, p);
    }