Java增加数组大小

Question

I have the following code that takes integers and stores it in a array of booleans according to the position. I have a method include that allows the user to input more numbers into the array however if the number is bigger than the array size then I need to increase the size. I am aware that you can't do much with arrays once they are made just change what's in each position. Is there a quick way to make it bigger or could I use arraylists to keep the array size changing?

public class ISet {
    public int max;
    boolean[] numArray;


    ISet(int a) {
        this.size = a;
        this.numArray = new boolean[size];

    }

    public void include(int n) {
        if (n > size) {
            this.size = n;
            numArray[n]=true;

        }
        else

            numArray[n]=true;


        }

Answer 1

If you want to make it bigger yourself you can use Arrays.copyOf(numArray, newLength) which will copy your array into a new new array of the specified length adding falses at the end if the new length is longer than the original.

Otherwise you can use an ArrayList.

Answer 2

You should use an ArrayList.

Normal arrays have a fixed size in Java.

Answer 3

You can either simply use an ArrayList, although it'll have to be ArrayList<Boolean> as opposed to boolean (the primitive data type). Probably the easiest solution.

The other option would be to create a new, larger array and copy every element from the current array to the new one when the size of the current array is exceeded.

Answer 4

For "normal" code you should use ArrayList instead.

For application that use extreme huge arrays, the array needs much less memory, than the ArrayList, because an Object needs 4 at least 4 times (16 bytes) more memory than a primitive.

For such special situations, you can use Arrays.copyOf() which copies the content into a new bigger array. See also src cocde of ArrayList.java