Stack

/**
 *  Creates a stack with an array.
 * <p>
 *  @author Mustafa Alparslan <mustafa.alparslan@boun.edu.tr>
 *  @version 1.0
 */
public class Stack {
    Character[] arr;
    int size;

    Stack()
    {
        this.arr = new Character[10];
        this.size = 10;
    }
    /**
     * Checks whether the stack is empty or not.
     * @return returns true if it is empty.
     */
    public boolean isEmpty()
    {
        if(arr[0] == null)
        return true;

        return false;
    }
    /**
     * Adds a new char to the stack.
     * If stack is full uses the method {@link #expandArr()} to expand stack.
     * @param ch is the character which will be added to stack.
     */
    public void push(char ch)
    {
        if(this.isFull()){
            this.expandArr();
        }
        arr[this.position(arr)] = ch;

    }
    /**
     * Takes the last character from stack and removes from stack.
     * @return the last char of the stack.
     */
    public char pop()
    {
        char temp =arr[this.position(arr)-1];
        arr[this.position(arr)-1]=null;
        return temp;
    }

    /**
     * Checks whether stack is full or not.
     * @return true if stack is full.
     */
    public boolean isFull()
    {
        if(arr[size-1] != null)
        return true;

        return false;
    }
    /**
     * Expands the size of stack by two.
     * Initially creates a new Temp char array and copy the values
     * from old stack to Temp.
     * Finally expands the size of stack and adds them one by one from the
     * Temp array.
     */
    public void expandArr()
    {
        Character[] temp = new Character[size];
        for(int i = 0; i < arr.length; i++){
            temp[i] = this.arr[i];
        }
        size = size*2;
        this.arr = new Character[size];
        for(int i = 0; i < temp.length; i++){
            arr[i] = temp[i];
        }
    }

    /**
     * Finds the current available position in an array
     * @param arry is the array which will be examined.
     * @return the current position.
     */
    public int position(Character[] arry)
    {
        int position = 0;
        for(int i = 0; i < arry.length; i++){
            if(arry[i] == null){
                position = i;
                break;
            }
        }
        return position;
    }
}