package Stack;

/*
    @author: Roderland
    @create: 2020-08-10---21:12
*/
/*
    自编数组实现简单栈
 */
public class MyArrayStack<E> {

    private static final int DEFAULT_CAPACITY = 10;

    private E[] array;

    private int elementCount = 0;

    public MyArrayStack(int capacity) { array = (E[])new Object[capacity]; }

    public MyArrayStack() { array = (E[])new Object[DEFAULT_CAPACITY]; }

    public void push(E o) {
        if (elementCount >= array.length) expansion();
        array[elementCount++] = o;
    }

    private void expansion() {
        E[] newArray = (E[]) new Object[array.length*2];
        //System.arraycopy(array, 0, newArray, 0, array.length);
        for (int i = 0; i < array.length; i++) {
            newArray[i] = array[i];
        }
        array = newArray;
    }

    public E peek() {
        EmptyCheck();
        return array[elementCount-1];
    }

    public E pop() {
        EmptyCheck();
        return array[--elementCount];
    }

    public boolean isEmpty() {
        return elementCount == 0;
    }

    public int size() {
        return elementCount;
    }

    private void EmptyCheck() {
        if (isEmpty())
            throw new IndexOutOfBoundsException("栈空");
    }

}