equivalent to push() or pop() for arrays?

Solution 1:

In Java an array has a fixed size (after initialisation), meaning that you can't add or remove items from an array.

int[] i = new int[10];

The above snippet mean that the array of integers has a length of 10. It's not possible add an eleventh integer, without re-assign the reference to a new array, like the following:

int[] i = new int[11];

In Java the package java.util contains all kinds of data structures that can handle adding and removing items from array-like collections. The classic data structure Stack has methods for push and pop.

Solution 2:

Use Array list http://developer.android.com/reference/java/util/ArrayList.html

Solution 3:

For those who don't have time to refactor the code to replace arrays with Collections (for example ArrayList), there is an alternative. Unlike Collections, the length of an array cannot be changed, but the array can be replaced, like this:

array = push(array, item);

The drawbacks are that

the whole array has to be copied each time you push, and
the original array Object is not changed, so you have to update the variable(s) as appropriate.

Here is the push method for String:
(You can create multiple push methods, one for String, one for int, etc)

private static String[] push(String[] array, String push) {
    String[] longer = new String[array.length + 1];
    for (int i = 0; i < array.length; i++)
        longer[i] = array[i];
    longer[array.length] = push;
    return longer;
}

This alternative is more efficient, shorter & harder to read:

private static String[] push(String[] array, String push) {
    String[] longer = new String[array.length + 1];
    System.arraycopy(array, 0, longer, 0, array.length);
    longer[array.length] = push;
    return longer;
}

Solution 4:

You can use Arrays.copyOf() with a little reflection to make a nice helper function.

public class ArrayHelper {
    public static <T> T[] push(T[] arr, T item) {
        T[] tmp = Arrays.copyOf(arr, arr.length + 1);
        tmp[tmp.length - 1] = item;
        return tmp;
    }

    public static <T> T[] pop(T[] arr) {
        T[] tmp = Arrays.copyOf(arr, arr.length - 1);
        return tmp;
    }
}

Usage:

String[] items = new String[]{"a", "b", "c"};

items = ArrayHelper.push(items, "d");
items = ArrayHelper.push(items, "e");

items = ArrayHelper.pop(items);

Results

Original: a,b,c

Array after push calls: a,b,c,d,e

Array after pop call: a,b,c,d

Solution 5:

You can use LinkedList. It has methods peek, poll and offer.