通用协议栈阵列 [英] Generic Stack Array

问题描述

我要实现一个通用的堆栈，但是当我尝试建立项目我有我想不出一个错误。这里的code：

I have to implement a generic stack, but when I try to build the project I have an error that I can't figure out. Here's the code:

Stack.java - >接口

Stack.java -> interface

package stack;

public interface Stack <T> {
    public boolean isEmpty();
    public boolean isFull();
    public void push(T x) throws StackFullException;
    public boolean offer(T x);
    public T pop() throws StackEmptyException;
    public T poll();
    public T peek() throws StackEmptyException;
    public T element();
}

StackArray.java - >的接口的实现

StackArray.java -> the implementation of the interface

package stack;

public class StackArray <T extends Number> implements Stack {
    static int max;
    private int nr;
    private T[] stack;

    public StackArray(int size){
        nr=0;
        stack=(T[])(new Object[size]);
        max=size;
    }
    public boolean isEmpty() {
        if (nr<=0)
            return true;
        return false;
    }
    public boolean isFull() {
        if (nr==max-1)
            return true;
        return false;
    }
    public void push(Object x) throws StackFullException{
        if(isFull())
            throw new StackFullException();
        else
            stack[nr++]=(T)x;
    }
    public boolean offer(Object x) {
        if(isFull())
            return false;
        else
        {
            stack[nr++]=(T)x;
            return true;
        }
    }

    public T pop() throws StackEmptyException {
        T aux=(T)(new Object());
        if(isEmpty())
            throw new StackEmptyException();
        else
            {
                aux=stack[nr];
                stack[nr]=null;
                nr--;
                return aux;
            }
        }

    public T poll() {
        T aux=(T)(new Object());
        if(isEmpty())
            return null;
        else
        {
             aux=stack[nr];
             stack[nr]=null;
             nr--;
             return aux;
        }

    }

    public T peek() throws StackEmptyException {
        if(isEmpty())
            throw new StackEmptyException();
        else
            return stack[nr];
    }

    public T element() {
        if(isEmpty())
            return null;
        else
            return stack[nr];
    }

}

和主类：

package stack;

public class Main {
    public static void main(String[] args) throws StackFullException, StackEmptyException {
        StackArray stiva=new StackArray(10);
        for(int i=1; i<10; i++)
            stiva.push(i);
        for(int i=1; i<10; i++)
            System.out.print(stiva.pop()+" ");
    }

}

当我尝试建立我收到以下错误项目：

When I try to build the project I receive the following error:

Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Ljava.lang.Number;
        at stack.StackArray.<init>(StackArray.java:10)
        at stack.Main.main(Main.java:5)
Java Result: 1

谁能帮我？谢谢！

Can anyone help me? Thanks!

推荐答案

的删除 T [] 是号码[] 因为上界 > T 是编号。因此，你的栈真是声明为号码[] 不是对象[] 。在你的构造你想分配对象[] 到栈。创建一个号码[] 代替。

The erasure of T[] is Number[] because the upper bound of T is Number. Thus your stack is really declared as a Number[] not an Object[]. In your constructor you are trying to assign an Object[] to stack. Create a Number[] instead.

stack=(T[])(new Number[size]);

顺便说一句，你可能想

As an aside, you probably want

public class StackArray <T extends Number> implements Stack<T>

您不应该实现类的原始版本。其结果是，你需要更新其他方法（如推（T）而不是推（对象））

You shouldn't implement the raw version of the class. As a consequence you'll need to update other methods (e.g. push(T) instead of push(Object)).

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