Stack接口：

public interface MyStack {
    //進棧
    Object push(Object s);
    //出棧
    Object pop();
    //判斷空
    boolean isEmpty();
    //查看棧頂元素
    Object peek();



}

stack接口實現(xiàn)類

public class MyStackImpl implements MyStack {
    private int top = -1; //棧頂
    private static final int MAX_CAPACITY = Integer.MAX_VALUE - 8;
    private static final int DEFAULT_CAPACITY = 10;
    private Object[] objs;

    public MyStackImpl() {
        this(DEFAULT_CAPACITY);
    }
    public MyStackImpl(int capacity) {
        if (capacity < 0 || capacity > MAX_CAPACITY) {
            throw new IllegalArgumentException("capacity=" + capacity);
        }
        objs = new Object[capacity];
    }

    @Override
    public Object push(Object obj) {
        if(top == objs.length - 1){
            this.grow();
        }
       return objs[++top]=obj;
    }

    private void grow(){  //擴容
        objs = Arrays.copyOf(objs, objs.length + (objs.length>>1));
    }


    @Override
    public Object pop() {
        if(isEmpty())
            throw new NullPointerException("Stack is empty!");
        return objs[top--];

}

    @Override
    public boolean isEmpty() {
        if (top==-1) {
            return true;
        }else{
            return false;
        }
    }

    @Override
    public Object peek() {
        if (isEmpty()){
            throw new EmptyStackException();
        }else{
            return objs[top];
        }
    }

}