栈Stack --- 数组实现

栈最大的一个特点就是先进后出(FILO—First-In/Last-Out)。

/**
 * 栈：后进先出
 * Created by fred on 2018/7/31.
 */
public class MyStack {
    private int[] elements;
    private int size;
    private final int DEFAULT_CAPACITY = 2;

    public MyStack(){
        elements = new int[DEFAULT_CAPACITY];
    }

    //判断是否为空
    public boolean isEmpty(){
        return size == 0;
    }

    //获取栈的长度
    public int getSize(){
        return size;
    }

    //数据入栈
    public void push(int value){
        if(size >= elements.length){
            int[] tmp = new int[elements.length * 2];
            System.arraycopy(elements, 0, tmp, 0, elements.length);
            elements = tmp;
        }
        elements[size++] = value;
    }

    //出栈
    public int pop(){
        if(isEmpty()){
            System.out.println("栈为空");
            return -1;
        }
        else {
            return elements[--size];
        }
    }
}