我的Java应用程序中的Caugth ClassCastException

使用数组的队列实现,但出现异常.

我有一个名为Queue的接口,其中通用ArrayQueue作为队列接口ArrayQueueTest的实现类作为我的主要类来测试代码.

public interface Queue<E>
{
    public void enqueue(E e);//insert an element in a queue
    public E dequeue();/delete an element in queue and return that element
    public int size();//give the number of elements in an queue
    public E first();//give the first element of queue if any but not removing it
    public boolean isEmpty();//indicate whether queue is empty or not
}    

public class ArrayQueue<E> implements Queue<E>
{   
    E [] data;   //array based implementation queue
    int front;   //indicating the first element of queue
    int size;   //size of queue indicator
    ArrayQueue(int x)    //initialization of queue
{
    data=(E [])(new Object[x]);     
}
public boolean isEmpty()
{
    return size==0;
}
public int size()
{
    return size;
}
public E first()
{
    return data[front];
}
public E dequeue()
{   
    if(isEmpty())   
    {  
        System.out.println("queue is empty");
        return null;
    }
    E ans=data[front];
    data[front]=null;
    front=(front+1)%data.length;
    size--;        
    return ans;
}
public void enqueue(E e)
{
    if(size==data.length)
    {
        System.out.println("size is full");
        return;
    }
    data[(front+size)%data.length]=e;
    size++;
}
}     

public class ArrayQueueTest 
{

    public static void main(String[] args)
    {
        System.out.println("welcome");
        ArrayQueue <Integer>aq=new ArrayQueue<Integer>(5);
        aq.enqueue(new Integer(5));  
        aq.enqueue(new Integer(6));
        aq.enqueue(new Integer(0)); 
        aq.enqueue(new Integer(8));
        System.out.println(aq.size());

        for(int i=0;i<aq.size();i++)    //loop to print the data of queue
        {  
            // Object ob=aq.data[i];    //why i will get an exception if i did not make a comment to this line
            System.out.println(aq.data[i]); /*why i am getting a ClassCastException getting at this line */
        }
    }
}

解决方法:

您将忽略编译时警告.这从来不是一个好兆头.

该警告基本上告诉您不能使用E []进行强制类型转换.基本上会在编译时通过警告删除此强制转换.

数据现在基本上在运行时成为Object []数组,并在这种情况下使用,编译器在需要强制转换的地方添加了(E)这样的强制转换,例如Integer i =(Integer)aq.dequeue();.当您访问数组时,例如((Integer [])aq.data)[i],Java也会执行此操作,这实际上是在编译时删除了泛型的影响.

尽管java可以正确帮助您,但它也向您显示Object []不是Integer [].如果java在编译时没有删除泛型,它将在警告现在所在的行出错.

您应该通过提供2种方法(例如Object[] Collections.toArray()和E[] toArray(E[]))来解决数据问题

标签：generic-programming,classcastexception,generics,queue,java
来源： https://codeday.me/bug/20191027/1944101.html