从原始数组中删除元素

Question

I have a primitive type array from which I want to remove an element at the specified index. What is the correct and efficient way to do that?

I am looking to remove the element in the way mentioned below

long[] longArr = {9,8,7,6,5};
int index = 1;

List list = new ArrayList(Arrays.asList(longArr));
list.remove(index);
longArr = list.toArray(); // getting compiler error Object[] can't be converted to long[]

but the above approach looks to work with with Object only not with primitives.

Any alternative to that? I can not use any third party/additional libraries

Answer 1

You need to create a new array and copy the elements; eg something like this:

public long[] removeElement(long[] in, int pos) {
    if (pos < 0 || pos >= in.length) {
        throw new ArrayIndexOutOfBoundsException(pos);
    }
    long[] res = new long[in.length - 1];
    System.arraycopy(in, 0, res, 0, pos);
    if (pos < in.length - 1) {
        System.arraycopy(in, pos + 1, res, pos, in.length - pos - 1);
    }
    return res;
}

NB: the above has not been tested / debugged ....

You could also do the copying using for loops, but arraycopy should be faster in this case.

The org.apache.commons.lang.ArrayUtils.remove(long[], int) method most likely works like the above code. Using that method would be preferable ... if you were not required to avoid using 3rd-party open source libraries. (Kudos to @Srikanth Nakka for knowing / finding it.)

The reason that you can't use an list to do this is that lists require an element type that is a reference type.

Answer 2

In addition to the answer by StephenC, have a look at https://www.cs.cmu.edu/~adamchik/15-121/lectures/Arrays/arrays.html .

It explains java arrays pretty well.

Answer 3

Use org.apache.commons.lang.ArrayUtils.

long[] longArr = {9,8,7,6,5};
int index = 1;
longArr=ArrayUtils.remove(longArr, index);

Answer 4

Integer[] arr = new Integer[] {100,150,200,300};

List<Integer> filtered = Arrays.asList(arr).stream()
    .filter(item -> item < 200)
    .collect(Collectors.toList());