这为什么会报错（多线程或ArrayList）？

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英文:

Why does this gives me an error (Multi Thread or ArrayList)?

问题

  1. ArrayList<Nemico> nemici = o_orda.getNemici();
  2. for (Nemico nemico : nemici) {
  3.     if (Collisioni.ControllaCollisioni(o_navicella, nemico)) {
  4.         nemici.remove(nemico);
  5.         this.o_navicella.vita -= 10;
  6.         break;
  7.     }
  8.     for (Proiettile pro : proiettili) {
  9.         System.out.println("s1");
  10.         if (Collisioni.CollsioniProiettile(pro, nemico)) {
  11.             System.out.println("s2");
  12.             nemici.remove(nemico);
  13.             System.out.println("s3");
  14.             proiettili.remove(pro);
  15.             System.out.println("s4");
  16.             break;
  17.         }
  18.         System.out.println("s5");
  19.     }
  20.     if (ControllaSconfitta()) {
  21.         this.giocON = false;
  22.         Disegna();
  23.     }
  24. }

This is the code, I'm sure it will help you.
This code is in a function that checks and updates everything every n milliseconds.

Thanks for the help

  1. Exception in thread "Thread-7" java.util.ConcurrentModificationException
  2. 	at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:901)
  3. 	at java.util.ArrayList$Itr.next(ArrayList.java:851)
  4. 	at java.lang.Thread.run(Thread.java:745)

and it freezes the game when the collision happens.

  2. <details>
  3. <summary>英文:</summary>
  5. I have two threads which are running and I need to control if the bullet is touching the enemy but it gives me this problem where I printed &quot;s4&quot;. Any idea what happened there? I&#39;m quite a beginner. I&#39;m using Java.

ArrayList<Nemico> nemici= o_orda.getNemici();
for (Nemico nemico : nemici) {
if(Collisioni.ControllaCollisioni(o_navicella, nemico)){
nemici.remove(nemico);
this.o_navicella.vita-=10;

  1.             break;
  2.         }
  3.         for (Proiettile pro : proiettili){
  4.             System.out.println(&quot;s1&quot;);
  5.                 if(Collisioni.CollsioniProiettile(pro, nemico)){
  6.                     System.out.println(&quot;s2&quot;);
  7.                     nemici.remove(nemico);
  8.                     System.out.println(&quot;s3&quot;);
  9.                     proiettili.remove(pro);
  10.                     System.out.println(&quot;s4&quot;);
  11.                     break;
  12.                     
  13.             }
  14.                 System.out.println(&quot;s5&quot;);
  15.         }
  16.        
  17.         if(ControllaSconfitta()){
  18.             this.giocON=false;
  19.             Disegna();
  20.         }
  21.     }
  2. This is the code, I&#39;m sure it will help you. 
  3. This code is in a function that checks and update everything every n millisecond.
  5. Thanks for the help

Exception in thread "Thread-7" java.util.ConcurrentModificationException
at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:901)
at java.util.ArrayList$Itr.next(ArrayList.java:851)
at java.lang.Thread.run(Thread.java:745)

  1. and it freeze the game when the collsion happens.
  6. </details>
  9. # 答案1
  10. **得分**: 1
  12. _以下代码已经更新以使用Iterator.remove()，而不是ArrayList.remove()。感谢@PeterRader澄清了它们的使用方法。_
  14. ---
  16. 如果您在迭代ArrayList时打算对其进行修改，不应直接使用for-each循环进行迭代。有两种替代方法，一种是使用迭代器避免直接迭代ArrayList本身，另一种是使用Java 8的removeIf()函数。
  18. 我将给出一个简单（经过测试的）使用迭代器的示例，然后尝试修改您的代码以执行相同的操作：
  20. **迭代器示例**
  21. ```java
  22. import java.util.ArrayList;
  23. import java.util.Arrays;
  24. import java.util.Iterator;
  26. public class IteratorExample {
  28.     public static void main(String[] args) {
  30.         ArrayList<Integer> arrList = new ArrayList<Integer>(Arrays.asList(1, 2, 3));
  32.         // 获取一个迭代器以迭代arrList中的整数
  34.         Iterator<Integer> iterator = arrList.iterator();
  36.         // 当迭代器有下一个元素时，使用.next()访问此元素并将其打印出来。
  37.         while (iterator.hasNext()) {
  38.             System.out.println(iterator.next());
  39.         }
  41.     }
  42. }

修改您的代码以使用迭代器

对于此版本中可能存在的拼写错误或语法错误，我深感抱歉 - 我无法对其进行测试，但鉴于这只是一个小片段的代码，错误应该不会太多，希望您可以使用上述示例进行修复。 不要忘记也导入java.util.Iterator！

  1. ArrayList<Nemico> nemici = o_orda.getNemici();
  3. Iterator<Nemico> nemiciIterator = nemici.iterator();
  5. while (nemiciIterator.hasNext()) {
  7.     nemico = nemiciIterator.next();
  9.     if (Collisioni.ControllaCollisioni(o_navicella, nemico)) {
  10.         nemiciIterator.remove();
  11.         this.o_navicella.vita -= 10;
  12.         break;
  13.     }
  15.     Iterator<Proiettile> proIterator = proiettili.iterator();
  17.     while (proIterator.hasNext()) {
  19.         pro = proIterator.next();
  21.         if (Collisioni.CollsioniProiettile(pro, nemico)) {
  22.             nemiciIterator.remove();
  23.             proIterator.remove();
  24.             break;
  25.         }
  26.     }
  28.     if (ControllaSconfitta()) {
  29.         this.giocON = false;
  30.         Disegna();
  31.     }
  32. }
  33. ...

资源

这是一个相关的资源。它还包括使用removeIf()的示例！https://www.baeldung.com/java-concurrentmodificationexception。

英文:

The below code has been updated to use Iterator.remove() instead of ArrayList.remove(). Thank you to @PeterRader for clarifying how these should be used.

If you are intending to modify an ArrayList while iterating over it, you should not use a for-each loop to iterate over it directly. There are two alternative approaches, using an iterator to avoid iterating over the ArrayList itself, or using Java 8's removeIf() function.

I will give a simple (and tested) example of using an iterator, and then attempt to modify your code to do the same thing:

Iterator Example

  1. import java.util.ArrayList;
  2. import java.util.Arrays;
  3. import java.util.Iterator;
  5. public class IteratorExample{
  7.      public static void main(String []args){
  8.          
  9.         ArrayList&lt;Integer&gt; arrList = new ArrayList&lt;Integer&gt;(Arrays.asList(1,2,3));
  10.         
  11.         // Get an Iterator to iterate over the Integers in arrList
  12.         
  13.         Iterator&lt;Integer&gt; iterator = arrList.iterator();
  14.         
  15.         // While iterator hasNext element, access this element with .next() and print it. 
  16.         while(iterator.hasNext()) {
  17.             System.out.println(iterator.next());
  18.         }
  19.         
  20.         
  21.      }
  22. }

Modifying your code to use an iterator

Apologies for any spelling mistakes or syntax errors in this version - I have been unable to test it, but given it's only a small piece of code there shouldn't be many and hopefully you will be able to remedy them using the example above. Don't forget to import java.util.Iterator too!

  1. ArrayList&lt;Nemico&gt; nemici= o_orda.getNemici();
  3. Iterator&lt;Nemico&gt; nemiciIterator = nemici.iterator();
  5. while (nemiciIterator.hasNext()) {
  7.     nemico = nemiciIterator.next();
  9.     if(Collisioni.ControllaCollisioni(o_navicella, nemico)){
  10.         nemiciIterator.remove(nemico);
  11.         this.o_navicella.vita-=10;
  12.         break;
  13.     }
  15.     Iterator&lt;Proiettile&gt; proIterator = proiettili.iterator();
  17.     while (proIterator.hasNext()) {
  19.         pro = proIterator.next();
  21.         if(Collisioni.CollsioniProiettile(pro, nemico)){
  22.             nemiciIterator.remove(nemico);
  23.             proIterator.remove(pro);
  24.             break;
  25.         }
  26.     }
  28.     if(ControllaSconfitta()){
  29.         this.giocON=false;
  30.         Disegna();
  31.         }
  32.     }
  33.     ...

Resources

Here is a relevant resource. This also includes an example of using removeIf()! https://www.baeldung.com/java-concurrentmodificationexception.

huangapple
  • 本文由 发表于 2020年3月15日 07:02:40
  • 转载请务必保留本文链接：https://go.coder-hub.com/60688124.html
  • arraylist
  • java
  • multithreading
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