Question

我有一个自定义的Stack类，它不操作数组，但是ArrayList<String>。

我的Stack类具有push，pop和size方法。

我正在通过 index 实例变量来跟踪索引。

我创建了一个数组来容纳三个元素。

这三个元素被压入堆栈。最后，弹出最后一个元素并将其打印在控制台上。

我总是收到自定义StackIsUnderflowing（）异常。

有人可以告诉我错误在哪里吗？

import java.util.ArrayList;


class StackIsUnderflowing extends Exception {

    private static final long serialVersionUID = 1 L;

    public StackIsUnderflowing() {
        super("Stack Underflowing");
    }
}

//main Stack class
public class Stack {
    private int index;
    //List of String literals
    private ArrayList < String > aStackArr = new ArrayList < String > ();
    private static int ZERO = 0;

    //constructor
    public Stack() {

        this.index = -1;
    }

    //return the size
    public int size() {
        return aStackArr.size();
    }

    //push value on to Stack add value to List of String input variable
    public void push(String anInt) {
        index = aStackArr.size() - 1;

        aStackArr.add(anInt);

        System.out.println(index + aStackArr.get(index));

    }

    //pop values from input variable
    public String pop() {

        try {
            if (index < Stack.ZERO) {
                throw new StackIsUnderflowing();
            } else {
                String result = aStackArr.remove(index);

                index = aStackArr.size() - 1;
                return result;
            }

        } catch (Exception e) {
            System.out.println(e.getMessage());
            System.exit(-1);
            return "-1";
        }
    }

    //peek into LIFO top input literal

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Stack aStack = new Stack();
        String[] names = new String[3];
        names[0] = "ll";
        names[1] = "cc";
        names[2] = "dd";
        String tmp;

        for (int i = 0; i < aStack.size(); ++i) {
            System.out.println(names[i]);
            aStack.push(names[i]);


        }
        tmp = aStack.pop();

        System.out.println(tmp);
    }
}

Answer 1

问题是您在index = aStackArr.size() - 1;之前分配了aStackArr.add(anInt);。方法push(String anInt)应该是这样的：

//push value on to Stack add value to List of String input variable
    public void push(String anInt)
    {
        aStackArr.add(anInt);
        index = aStackArr.size() - 1;
        System.out.println(index + aStackArr.get(index));
    }

此外，这是添加推入字符串的代码的问题，循环位于aStack.size()而非names.length

这是完整的代码（格式化的）

import java.util.ArrayList;

class StackIsUnderflowing extends Exception
{

    private static final long serialVersionUID = 1L;

    public StackIsUnderflowing()
    {
        super("Stack Underflowing");
    }
}

//main Stack class
public class Stack
{
    private int index;
    //List of String literals
    private ArrayList<String> aStackArr = new ArrayList<String>();
    private static int ZERO = 0;

    //constructor
    public Stack()
    {
        this.index = -1;
    }

    //return the size
    public int size()
    {
        return aStackArr.size();
    }

    //push value on to Stack add value to List of String input variable
    public void push(String anInt)
    {
        aStackArr.add(anInt);
        index = aStackArr.size() - 1;
        System.out.println(index + aStackArr.get(index));
    }

    //pop values from input variable
    public String pop()
    {
        try
        {
            if (index < Stack.ZERO)
            {
                throw new StackIsUnderflowing();
            }
            else
            {
                String result = aStackArr.remove(index);
                index = aStackArr.size() - 1;
                return result;
            }

        }
        catch (Exception e)
        {
            e.printStackTrace();
            System.exit(-1);
            return "-1";
        }
    }

    //peek into LIFO top input literal

    public static void main(String[] args)
    {
        // TODO Auto-generated method stub
        Stack aStack = new Stack();
        String[] names = new String[3];
        names[0] = "ll";
        names[1] = "cc";
        names[2] = "dd";
        String tmp;

        for (int i = 0; i < names.length; ++i)
        {
            System.out.println(names[i]);
            aStack.push(names[i]);
        }
        tmp = aStack.pop();
        System.out.println(tmp);
    }
}

我自定义的Stack类总是抛出StackIsUnderflowing异常：为什么？

1 个答案: