Stack Implementation

REF.

public class MyStack {
    private int[] storage;// 存放栈中元素的数组
    private int capacity;// 栈的容量
    private int count;// 栈中元素数量
    private static final int GROW_FACTOR = 2;

    // 不带初始容量的构造方法。默认容量为8
    public MyStack() {
        this.capacity = 8;
        this.storage = new int[8];
        this.count = 0;
    }

    // 带初始容量的构造方法
    public MyStack(int initialCapacity) {
        if (initialCapacity < 1)
            throw new IllegalArgumentException("Capacity too small.");

        this.capacity = initialCapacity;
        this.storage = new int[initialCapacity];
        this.count = 0;
    }

    // 入栈
    public void push(int value) {
        if (count == capacity) {
            ensureCapacity();
        }
        storage[count++] = value;
    }

    // 确保容量大小
    private void ensureCapacity() {
        int newCapacity = capacity * GROW_FACTOR;
        storage = Arrays.copyOf(storage, newCapacity);
        capacity = newCapacity;
    }

    // 返回栈顶元素并出栈
    private int pop() {
        if (count == 0)
            throw new IllegalArgumentException("Stack is empty.");
        count--;
        return storage[count];
    }

    // 返回栈顶元素不出栈
    private int peek() {
        if (count == 0) {
            throw new IllegalArgumentException("Stack is empty.");
        } else {
            return storage[count - 1];
        }
    }

    // 判断栈是否为空
    private boolean isEmpty() {
        return count == 0;
    }

    // 返回栈中元素的个数
    private int size() {
        return count;
    }

}