how to delete a value from an array and shrink the array?

Perhaps converting your array to an arraylist then using the remove() method of the arraylist class would work. Then you could take said arraylist and convert it back to an array. Both conversions could work with a for-loop.

Another option would be to take an array. Find the index of the value you want to remove. Then make a for loop starting at that index that shifts all of the values to the right of that index then puts those values one index to the left.

Here is re sizable array that will change capacity on remove and add operations (when capacity is reached). Did not test this much but looks okay.

public class ArrayBackedIndexedCollection {

    private int size;
    private int capacity;
    private Object[] elements;

    public ArrayBackedIndexedCollection(){      

        this.capacity = 1;
        this.elements = new Object[capacity];
    }

    public ArrayBackedIndexedCollection(int initalCapacity){

        /***************************************************
         if initial capacity is less then 1 -> throw
         exception
         **************************************************/
        this.capacity = initalCapacity;
        this.elements = new Object[initalCapacity];

    }


    public int size(){

        return size;
    }

    public void add(Object object){

        // if capacity is reached
        if ( size == capacity){


            Object[] tmp = new Object[capacity];
            // backup current array
            System.arraycopy(elements, 0, tmp, 0, elements.length);

           // re size to double capacity 
            elements = new Object [2*capacity];

           // copy backup into re sized elements array
            System.arraycopy(tmp, 0, elements, 0, tmp.length);

            capacity = 2 * capacity;

        }

        this.elements[size] = object;
        size++;
    }

    public Object get(int index){

        return this.elements[index];    
    }

    public void remove(int index){

        elements[index] = null;
        size --;

        System.arraycopy(elements, index, elements, index + 1, size() - index);

    }

    public void insert(Object value, int position){

        //...
    }

}

Once you have created an array object in java you cannot resize it. If you want an array of different size you will have to create a new array and then populate it from scratch.

As you can imagine this is very inefficient and performance heavy. You are better off using an ArrayList or LinkedList. As a general rule you should favour collections over arrays, but if you're just looking to solve the challenge here's how I'd do it:

public static int[] shrinkArray(int keyToRemove, int[] arrayToRemoveFrom){
    int[] resultArray = new int[arrayToRemoveFrom.length - 1];//new array is one smaller
    boolean itemRemoved = false;
    for(int i = 0, j = 0; i < resultArray.length; i++, j++){
        if(!itemRemoved && arrayToRemoveFrom[i] == keyToRemove){
            itemRemoved = true;//boolean so you only get in here once
            i--;//decrease i for result array so you done leave a blank space 
        }else{
            resultArray[i] = arrayToRemoveFrom[j];
        }
    }
    return resultArray;
}