如何处理不会导致错误的 emptycollectionsException？

huangapple
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英文:

How to handle a emptycollectionsException that doesn't result in an error?

问题

今天我有一个关于代码中的EmptyCollectionException的问题。以下是重要部分：

  1. public static void main (String [] args) //程序的主类
  2. {
  3.     Scanner input = new Scanner(System.in);
  4.     ArrayStack<String> stk = new ArrayStack<String>();
  5.     int menu = 0; //初始化菜单
  6.     do {
  7.         System.out.println("堆栈菜单选项\n1.入栈 \n2.出栈 \n3.查看栈顶元素 \n4.显示栈 \n5.退出");
  8.         System.out.println();
  9.         System.out.print("请输入您的选择：");
  10.         menu = Integer.parseInt(input.next()); //允许用户输入选择。
  11.         switch (menu) {
  12.             case 1: //如果选择了1，则用户可以将元素入栈。
  13.                 System.out.print("请输入元素：");
  14.                 String element = input.next();
  15.                 stk.push(element);
  16.                 break;
  17.             case 2: //如果选择了2，则从栈顶弹出元素。
  18.                 System.out.println("弹出的元素为：" + stk.pop());
  19.                 break;
  20.             case 3: //如果选择了3，则查看栈顶元素但不删除。
  21.                 System.out.println("栈顶元素为：" + stk.peek());
  22.                 break;
  23.             case 4: //如果选择了4，则显示整个栈。
  24.                 System.out.println("完整的栈为：\n" + stk);
  25.                 break;
  26.             default:
  27.                 System.out.println("选择了退出，程序正在关闭。"); //关闭程序
  28.                 return;
  29.         }
  30.     } while (true); //只要输入了1-5，程序就会循环。
  31. }

我遇到的错误是，当我尝试从空栈执行“出栈”操作时，会出现以下错误：

  1. 堆栈菜单选项
  2. 1.入栈 
  3. 2.出栈 
  4. 3.查看栈顶元素 
  5. 4.显示栈 
  6. 5.退出
  8. 请输入您的选择：2
  9. Exception in thread "main" jsjf.exceptions.EmptyCollectionException: 栈为空。
  10. 	at jsjf.ArrayStack.pop(ArrayStack.java:57)
  11. 	at jsjf.ArrayTest.main(ArrayTest.java:39)
  12. C:\Users\ADAIS\AppData\Local\NetBeans\Cache\8.2\executor-snippets\run.xml:53: Java 返回了：1
  13. 构建失败（总时间：3秒）

我知道是什么导致了这个错误，是Pop和Peek代码在使用EmptyCollectionException类：

  1. public T pop() throws EmptyCollectionException //从栈顶移除元素并返回引用。如果栈为空，则抛出EmptyStackException。
  2. {
  3.     if (isEmpty())
  4.         throw new EmptyCollectionException("stack");
  5.     top--;
  6.     T result = stack[top];
  7.     stack[top] = null;
  8.     return result;
  9. }
  11. public T peek() throws EmptyCollectionException //返回栈顶元素的引用。不从栈顶移除元素。如果栈为空，则抛出EmptyCollectionException。
  12. {
  13.     if (isEmpty())  
  14.         throw new EmptyCollectionException("stack");
  15.     return stack[top-1];
  16. }

而EmptyCollectionException类是这样的：

  1. public EmptyCollectionException(String collection)
  2. {
  3.     super("The " + collection + " is empty.");
  4. }

我想知道是否有人知道如何使它不会崩溃，而是循环显示“栈为空，请重试”之类的消息？这个代码的任务已经完成了，我只是想为了自己而修复它。

英文:

Today I have a question regarding the emptycollectionsException in my code. Here's the important bits

  1. public static void main (String [] args) //Main class of the program
  2. {
  3. Scanner input = new Scanner(System.in);
  4. ArrayStack&lt;String&gt; stk = new ArrayStack&lt;String&gt;();
  5. int menu = 0; //Initializes menu
  6. do {
  7. System.out.println(&quot;Stack Menu Selections\n1.Push \n2.Pop \n3.Peek \n4.Display \n5.Exit&quot;);
  8. System.out.println();
  9. System.out.print(&quot;Enter your Choice: &quot;);
  10. menu =Integer.parseInt(input.next()); //Allows the user to input a selection.
  11. switch (menu) {
  12. case 1: //If 1 is selected then the user can push an element into the stack.
  13. System.out.print(&quot;Enter element: &quot;);
  14. String element = input.next();
  15. stk.push(element);
  16. break;
  17. case 2: //If 2 is selected then the element at the top is popped from the stack. 
  18. System.out.println(&quot;Popped Element is &quot; + stk.pop());
  19. break;
  20. case 3: //If 3 is selected then the top element is peeked but not deleted.
  21. System.out.println(&quot;Peeking is &quot; + stk.peek());
  22. break;
  23. case 4: //If 4 is selected, then the full stack is displayed.
  24. System.out.println(&quot;Full Stack is: \n&quot; + stk);
  25. break;
  26. default: System.out.println(&quot;Exit selected, shutting down program.&quot;); //Closes program
  27. return;
  28. }
  29. }while(true); //Program loops as long as 1-5 are inputed.
  30. }

The error I'm facing is that when I go to "pop" an empty stack, it results in this

  1. Stack Menu Selections
  2. 1.Push 
  3. 2.Pop 
  4. 3.Peek 
  5. 4.Display 
  6. 5.Exit
  7. Enter your Choice: 2
  8. Exception in thread &quot;main&quot; jsjf.exceptions.EmptyCollectionException: The stack is empty.
  9. at jsjf.ArrayStack.pop(ArrayStack.java:57)
  10. at jsjf.ArrayTest.main(ArrayTest.java:39)
  11. C:\Users\ADAIS\AppData\Local\NetBeans\Cache\8.2\executor-snippets\run.xml:53: Java returned: 1
  12. BUILD FAILED (total time: 3 seconds)

I know what's causing it, an EmptyCollectionsException class that the Pop and Peek code is using

  1. public T pop() throws EmptyCollectionException //Removes the element that&#39;s at the top
  2. //of the stack and returns with a reference
  3. //to it. Throws an EmptyStackException if the
  4. //stack is empty
  5. {
  6. if (isEmpty())
  7. throw new EmptyCollectionException(&quot;stack&quot;);
  8. top--;
  9. T result = stack[top];
  10. stack[top] = null;
  11. return result;
  12. }
  13. public T peek() throws EmptyCollectionException //Returns a reference to the element that&#39;s
  14. //at the top of the stack. The element is 
  15. //not removed from the top of the stack.
  16. //throws an EmptycollectionException is the stack is empty
  17. {
  18. if (isEmpty())  
  19. throw new EmptyCollectionException(&quot;stack&quot;);
  20. return stack[top-1];
  21. }

which is

  1. public EmptyCollectionException(String collection)
  2. {
  3. super(&quot;The &quot; + collection + &quot; is empty.&quot;);
  4. }

I was wondering if anyone had any breadcrumbs on how to make it so that instead of crashing, it loops with a "Stack is empty, try again" kinda thing? The assignment for this code is already finished, I just wanna fix it for my own sake.

答案1

得分: 0

  1. 在调用 pop() 之前检查 isEmpty()。

或

  1. 处理异常：
  1.         do { 
  2. try { 
  3. switch (…) { 
  4. ….blah blah blah … 
  5. } 
  6. }
  7. catch (EmptyCollectionException ex) { 
  8. System.out.println("Nothing to pop"); 
  9. } 
  10. } while (true);
英文:
  1. Check isEmpty() before calling pop()

or

  1. Handle the exception:

    1. do { 
    2. try { 
    3. switch (…) { 
    4. ….blah blah blah … 
    5. } 
    6. }
    7. catch (EmptyCollectionException ex) { 
    8. System.out.println(&quot;Nothing to pop&quot;); 
    9. } 
    10. } while (true);

huangapple
  • 本文由 发表于 2020年9月12日 22:10:52
  • 转载请务必保留本文链接：https://go.coder-hub.com/63861180.html
  • arrays
  • crash
  • exception
  • java
  • stack
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