制作 .removeAll() 方法时出现 ConcurrentModificationException

Question

我有这样的代码

public class ListAnalyzer {
public static List<String> base;

public static void addOfflineToBase(String offline) {
    base.add(offline);
}

public static List<String> prepareArrayList() throws IOException {
    base = Files.readAllLines(Paths.get("/Users/noname/Desktop/test.txt").toAbsolutePath().normalize());
    List<String> part = base.subList(0, 200);
    base.removeAll(part);
    saveBase();
    return part;
}

当我尝试运行它时 - 我看到：

Unable to evaluate the expression Method threw 'java.util.ConcurrentModificationException' exception.

在线时我尝试base.removeAll(part) 我在这里看不到冲突。有人能帮助我吗？顺便说一句： saveBase() 只是将数据写入文本文件 UPD：堆栈跟踪

21:59:26: Executing task 'App.main() --scan'...

> Task :compileJava UP-TO-DATE
> Task :processResources NO-SOURCE
> Task :classes UP-TO-DATE

> Task :App.main() FAILED
2 actionable tasks: 1 executed, 1 up-to-date

Publishing a build scan to scans.gradle.com requires accepting the Gradle Terms of Service defined at https://gradle.com/terms-of-service. Do you accept these terms? [yes, no] Exception in thread "main" java.util.ConcurrentModificationException
 at java.base/java.util.ArrayList$SubList.checkForComodification(ArrayList.java:1445)
 at java.base/java.util.ArrayList$SubList.size(ArrayList.java:1185)
 at java.base/java.util.AbstractCollection.isEmpty(AbstractCollection.java:87)
 at com.lukaspradel.steamapi.webapi.request.GetPlayerSummariesRequest$GetPlayerSummariesRequestBuilder.<init>(GetPlayerSummariesRequest.java:41)
 at hexlet.code.App.getOnlineIds(App.java:39)
 at hexlet.code.App.start(App.java:21)
 at hexlet.code.App.main(App.java:16)

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':App.main()'.
> Process 'command '/Library/Java/JavaVirtualMachines/zulu-11.jdk/Contents/Home/bin/java'' finished with non-zero exit value 1

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 337ms

```lang-none

Answer 1

I need to understand how i can safely remove strings from base.

有两种方法：

添加一些应用程序级锁定，这样您就不会在其他内容迭代列表时尝试从列表中删除字符串。
使用并发集合类型而不是 List。（不清楚哪种集合类型最合适。没有合适的并发列表类型；即支持高效更新的类型。）并发集合类型在 java.util.concurrent package 中定义。

Answer 2

我想问题出在这几行：

List<String> part = base.subList(0, 200);
base.removeAll(part);

列表 part 实际上由列表 base 支持，因此 base 中的更改反映在 part 中。那可能会导致这样的异常。

要确认这一点，请您尝试：

List<String> part = new ArrayList<>(base.subList(0, 200));
base.removeAll(part);

另一种可能性，它与您的有所不同但相似：

 base.subList(0, 200).clear();

这将删除 0 到 200 范围内的所有元素，前提是所有元素都是唯一的。

制作 .removeAll() 方法时出现 ConcurrentModificationException

ConcurrentModificationException while making .removeAll() method

java

list

arraylist

concurrentmodificationexception