使用数组实现栈

使用数组实现栈

public class MyStack {

  // 存储数据
  private int[] storage;
  // 栈的容量
  private int capacity;
  // 栈中的元素
  private int count;
  // 栈扩大的比例
  private static final int GROW_FACTOR = 2;

  // 空构造法
  public MyStack() {
    this.storage = new int[8];
    this.capacity = 8;
    this.count = 0;
  }

  // 带容量的构造方法
  public MyStack(int capacity) {
    if (capacity < 1) {
      throw new IllegalArgumentException("capacity illegal");
    }

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

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

  // 扩展栈大小
  private void ensureCapacity() {
    int newCapacity = capacity * GROW_FACTOR;
    storage = Arrays.copyOf(storage, newCapacity);
    capacity = newCapacity;
  }

  // 数据出栈
  public int pop() {
    if (count == 0) {
      throw new IllegalArgumentException("Stack is empty.");
    }
    count--;
    return storage[count];
  }

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

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

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