简单的堆栈实现举例

public class Stack {
    private              Object[] elements;
    private              int      size                     = 0;
    private static final int      DEFAULT_INITIAL_CAPACITY = 16;

    public Stack() {
        elements = new Object[DEFAULT_INITIAL_CAPACITY];
    }

    public void push(Object e) {
        ensureCapacity();
        elements[size++]=e;
    }

    public Object pop(){
        if(size==0){
            throw new EmptyStackException();
        }
        Object result = elements[--size];
        elements[size]=null;
        return result;
    }

    public boolean isEmpty(){
        return size==0;
    }

    private void ensureCapacity() {
        if (elements.length == size) {
            elements = Arrays.copyOf(elements, 2 * size + 1);

        }
    }

}