//使用陣列來實現棧
package 陣列實現棧;

import java.util.Arrays;

interface StackADT {

    public void push(Object element);//壓棧

    public Object pop();//出棧

    public boolean isEmpty();//判斷是否為空棧

    public int size();

    public Object peek();

    public String toString();
}

public class Stack implements StackADT {

    private final int DEFAULT_SIZE = 3;  //預設陣列大小
    private int size = 0;
    private int capacity = 0;
    //top指向下一個能夠新增元素的位置  
    private int top = 0;
    private Object[] array;

    public Stack() {//設定陣列初始大小
        this.capacity = this.DEFAULT_SIZE;
        this.array = new Object[this.capacity];
        this.size = 0;
    }

    public Stack(int capacity) {  //控制陣列容量
        this.capacity = capacity;
        this.array = new Object[this.capacity];
        this.size = 0;
    }

    @Override
    public void push(Object element) {        //壓棧
        if (this.size < this.capacity) {
            this.array[top] = element;
            this.top++;
            this.size++;
        } else {
            enlarge();
            push(element);
        }
    }

    public void enlarge() {   //擴容
        this.capacity = this.capacity + this.DEFAULT_SIZE;
        Object[] newArray = new Object[this.capacity];
        System.arraycopy(array, 0, newArray, 0, array.length);
        Arrays.fill(array, null);
        this.array = newArray;
    }

    @Override
    public Object pop() { //檢視棧頂元素並將棧頂元素刪除
        Object element = (Object) this.array[top - 1];
        this.array[top - 1] = null;
        this.size--;
        return element;
    }

    @Override
    public boolean isEmpty() { //判斷棧是否為空
        return size == 0;
    }

    @Override
    public int size() { //返回棧的大小
        return size;
    }

    @Override
    public Object peek() {   //檢視棧頂元素但不刪除
        return (Object) this.array[this.top - 1];
    }

    public static void main(String[] args) {
        Stack s = new Stack();
        s.push(1);
        s.push(2);
        s.push(3);
        System.out.println(s.pop());
        System.out.println(s.size());

    }

}