My implementation of dynamic array

Question

Below is my implementation of dynamic array without help of library functions. Kindly provide your suggestions on design, coding style and algorithm.

MyDynamicArray.java

import java.util.NoSuchElementException;

public class MyDynamicArray<T>
{
    private int positionPointer=0;
    private int arraySize;
    private T[] dynamicArray;
    private static final int DEFAULT_ARRAY_SIZE=10;

    public MyDynamicArray()
    {
        this(DEFAULT_ARRAY_SIZE);
    }

    public MyDynamicArray(int arraySize)
    {
        this.arraySize=arraySize;
        dynamicArray=(T[]) new Object[arraySize];
    }

    public void addElement(T element)
    {
        adjustSize();
        dynamicArray[positionPointer]=element;
        positionPointer++;
    }

    public void addElementAtNode(int index, T element)
    {
        if(index<positionPointer)
        {
            dynamicArray[index]=element;
        }
        else
        {
            addElement(element);
            throw new ArrayIndexOutOfBoundsException("index "+index+" is greater than the size of array "+(positionPointer-1)+" \nElement added to end of array..");
        }
    }

    private void adjustSize()
    {
        if(positionPointer==arraySize)
        {
            increaseSize();
        }
        else if(positionPointer==(arraySize/4-1))
        {
            decreaseSize();
        }
    }

    private void increaseSize()
    {
        T[] tempArray=(T[]) new Object[2*arraySize];
        for(int i=0;i<positionPointer;i++)
        {
            tempArray[i]=dynamicArray[i];
        }
        dynamicArray=tempArray;
        arraySize=2*arraySize;
    }

    private void decreaseSize()
    {
        T[] tempArray=(T[]) new Object[(arraySize/4)];
        for(int i=0;i<positionPointer;i++)
        {
            tempArray[i]=dynamicArray[i];
        }
        dynamicArray=tempArray;
        arraySize=arraySize/4;
    }

    public int searchElement(T element)
    {
        for(int i=0;i<positionPointer;i++)
        {
            if(dynamicArray[i].equals(element))
            {
                return i;
            }
        }
        throw new NoSuchElementException("Element not found : "+element.toString());
    }

    public T getElementAtIndex(int index)
    {
        if(index<positionPointer)
        {
            return dynamicArray[index];
        }
        else
        {
            throw new ArrayIndexOutOfBoundsException("index "+index+" is greater than the size of array "+positionPointer);
        }
    }

    public void removeElement(T element)
    {
        int index=searchElement(element);
        if(index>0)
        {
            removeElementAtIndex(index);
        }
    }

    public void removeElementAtIndex(int index)
    {
        if(index<positionPointer)
        {
            for(int i=index;i<positionPointer-1;i++)
            {
                dynamicArray[index]=dynamicArray[index+1];
            }
            dynamicArray[positionPointer-1]=null;
            positionPointer--;
            adjustSize();
        }
        else
        {
            throw new ArrayIndexOutOfBoundsException("index "+index+" is greater than the size of array "+positionPointer);
        }
    }

    public int size()
    {
        return positionPointer;
    }

}

Answer 1

Advice 1

if(positionPointer==arraySize)

You should have always one space before and after a binary operator:

if(positionPointer == arraySize)

Advice 2

For Java, more conventional way of writing blocks is

if (...) {
    ...
}

instead of

if (...) 
{
    ...
}

Advice 3

Omit the arraySize and use dynamicArray.length instead.

Advice 4

private int positionPointer=0;

Just write

private int positionPointer;

since JVM initializes integer fields to zero by default.

Advice 5

You use positionPointer for keeping track of the number of elements in your data structure. For that very reason, I suggest you rename it to size.

Advice 6

public void addElementAtNode(int index, T element)
{
    if(index<positionPointer)
    {
        dynamicArray[index]=element;
    }
    else
    {
        addElement(element);
        throw new ArrayIndexOutOfBoundsException("index "+index+" is greater than the size of array "+(positionPointer-1)+" \nElement added to end of array..");
    }
}

Above, if the index is correct, you basically set an element instead of adding it. I suggest you rename it to set. Also, it seems strange what you do in the case if index is invalid.

Advice 7

In your increaseSize, you can just say:

dynamicArray = Arrays.copyOfRange(dynamicArray, 0, 2 * dynamicArray.length);

Also, same applies to decreaseSize:

dynamicArray = Arrays.copyOf(dynamicArray, dynamicArray.length / 4);

Advice 8

public int searchElement(T element)
{
    for(int i=0;i<positionPointer;i++)
    {
        if(dynamicArray[i].equals(element))
        {
            return i;
        }
    }
    throw new NoSuchElementException("Element not found : "+element.toString());
}

If the array contains a null value, if(dynamicArray[i].equals(element)) will throw. Also, conventional lists return the value -1 in case of missing element instead of throwing NoSuchElementException:

public int searcElement(T element) {
    for (int i = 0; i < positionPointer; ++i) {
        if (Objects.equals(element, dynamicArray[i])) {
            return i;
        }
    }

    return -1;
}

Advice 9

In removeElementAtIndex, instead of

dynamicArray[positionPointer-1]=null;
positionPointer--;

you can write

dymaicArray[--positionPointer] = null;

Advice 10

You make sure that the indices are not too large. However, you must make sure that they are not negative either.

Hope that helps.

Answer 2

In almost all methods for example in this one instead of

public void removeElement(T element)
{
    int index=searchElement(element);
    if(index>0)
    {
        removeElementAtIndex(index);
    }
}

should be

public void removeElement(T element)
{
    int index=searchElement(element);
    if(index >= 0)
    {
        removeElementAtIndex(index);
    }
}

Because otherwise the first element will get you an error.

Answer 3

In removeElementAtIndex, instead of

for(int i=index;i<positionPointer-1;i++)
{
    dynamicArray[index]=dynamicArray[index+1];
}

I think it should be

for(int i=index;i<positionPointer-1;i++)
{
    dynamicArray[i]=dynamicArray[i+1];
}