数据结构——栈（顺序栈）——Java

public class SqStackClass<E> {                       //顺序栈泛型类
    final int initcapacity = 10;                     //顺序栈的初始容量(常量)
    private int capacity;                            //存放顺序栈的容量
    private E[] data;                                //存放顺序栈中元素
    private int top;                                 //存放栈顶指针
    private int num;                                 //记录元素个数
    public SqStackClass() {                      //构造方法，实现data和size的初始化
        data = (E[]) new Object[initcapacity];        //强制转换为E类型数组
        capacity = initcapacity;
        top = -1;
    }
    private void updatecapacity(int newcapacity) {    //改变顺序栈的容量为newcapacity
        E[] newdata = (E[]) new Object[newcapacity];
        for (int i = 0; i < top; i++) {                       //复制原来的元素
            newdata[i] = data[i];
        }
        capacity = newcapacity;                        //设置新容量
        data = newdata;                                //仍由data标识数组
    }
    /**
     * 栈的基本运算算法
     */
    public boolean isEmpty() {                         //判断栈是否为空
        return top == -1;
    }
    public void push(E e) {                         //元素e进栈
        if (top == capacity - 1) {                       //顺序栈空间满时倍增容量
            updatecapacity(2 * (top + 1));
        }
        top++;                                        //栈顶指针增1
        data[top] = e;
        num++;                                       //元素+1
    }
    public E pop() {                                    //出栈操作栈顶
        if (isEmpty()) {
            throw new IllegalArgumentException("栈空");
        }
        E e = (E) data[top];
        top--;
        if (top + 1 > initcapacity && top + 1 == capacity / 4) { //满足条件则容量减半
            updatecapacity(capacity / 2);
        }
        num--;                                              //元素-1
        return e;
    }
    public E peek() {                                 //取栈顶元素操作
        if (isEmpty()) {
            throw new IllegalArgumentException("栈空");
        }
        return (E) data[top];
    }
    public String toString() {                        //将栈转换为字符串,不是基本运算，仅仅调试用
        String ans = "";
        for (int i = 0; i <= top; i++) {
            ans += data[i] + " ";
        }
        return ans;
    }
    //返回元素长度
    public int size() {
        return num;
    }
}