Stack

栈，先进后出的数据结构(后进先出)

• pop 弹出一个数据
• push 压入进栈

• isEmpty 是否为空

  /**
  * @author chenshun00@gmail.com
  * @since 2021/7/25 10:38 上午
  */
  public class TestStack<E> {
    private Object[] elements;
    private int location;
    private int initialCapacity = 16;
    public TestStack() {
        elements = new Object[initialCapacity];
        location = 0;
    }
    public void push(E data) {
        checkCapacity();
        elements[location] = data;
        location = location + 1;
    }
    @SuppressWarnings("unchecked")
    public E pop() {
        location = location - 1;
        final Object element = elements[location];
        elements[location] = null;
        return (E) element;
    }
    public int size() {
        return location;
    }
    private void checkCapacity() {
        boolean shouldResize = location / (initialCapacity * 1f) >= 0.75f;
        if (shouldResize) {
            initialCapacity = initialCapacity << 1;
        }
        Object[] temp = new Object[this.initialCapacity];
        System.arraycopy(elements, 0, temp, 0, location);
        elements = temp;
    }
    public static void main(String[] args) {
        TestStack<String> testStack = new TestStack<>();
        for (int i = 0; i < 16; i++) {
            testStack.push(i + "zz");
        }
        System.out.println(testStack.size());
        System.out.println(testStack.pop());
        System.out.println(testStack.pop());
        System.out.println(testStack.pop());
        System.out.println(testStack.pop());
        System.out.println(testStack.size());
    }
  }