比较数据编号，Iterator.remove() 抛出 NullPointerException

Question

我正在尝试制作一个可以比较整数的 Android 应用。但是，当我尝试比较整数并且我需要删除一些条目时，因为它们是多余的或它们不适合，我不能在不遇到 NullPointerException 的情况下使用 Iterator.remove()。这是具体的输出：

E/AndroidRuntime: FATAL EXCEPTION: main
          Process: com.daita.musicale, PID: 22649
          java.lang.UnsupportedOperationException
              at java.util.AbstractList.remove(AbstractList.java:638)
              at java.util.AbstractList$SimpleListIterator.remove(AbstractList.java:75)
              at com.daita.musicale.MainActivity.checkNotes(MainActivity.java:115)
              at com.daita.musicale.MainActivity$3.onClick(MainActivity.java:74)
              at android.view.View.performClick(View.java:5198)
              at android.view.View$PerformClick.run(View.java:21147)
              at android.os.Handler.handleCallback(Handler.java:739)
              at android.os.Handler.dispatchMessage(Handler.java:95)
              at android.os.Looper.loop(Looper.java:148)
              at android.app.ActivityThread.main(ActivityThread.java:5417)
              at java.lang.reflect.Method.invoke(Native Method)
              at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
              at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

这是给我错误的代码区域（在 com.daita.musicale.MainActivity.checkNotes(MainActivity.java:115)）。

public boolean[] checkNumbers(String code1, String code2) {
    if (code != null) {
        List<String> c1 = Arrays.asList(code1.replace("-1.0,", "").replace("null", "").split(","));
        List<String> c2 = Arrays.asList(code2.replace("-1.0,", "").replace("null", "").split(","));
        Iterator<String> c1iterator = c1.iterator();
        Iterator<String> c2iterator = c2.iterator();
        boolean strike = false;
        double prev = 0;
        int i = 0;
        boolean[] correctness = new boolean[c1.size()];
        while (c1iterator.hasNext()) {
            double c1hertz = Double.parseDouble(c1iterator.next());
            double c2hertz = Double.parseDouble(c2iterator.next());
            double difference = c1hertz - c2hertz;
            if (difference > -1 && difference < 1) {
                correctness[i] = true;
                double prevDifference = prev - c1hertz;
                if (prevDifference > -1 && prevDifference < 1) {
                    c1iterator.remove(); //specific issue location! (this is line 115 of MainActivity)
                    c2iterator.remove();
                    i = 0;
                    correctness = new boolean[c1.size()];
                } else {
                    prev = c1hertz;
                    correctness[i] = true;
                }
            } else {
                if (strike) {
                    correctness[i] = false;
                    try {
                        correctness[i - 1] = false;
                    } catch (ArrayIndexOutOfBoundsException aioobe) {
                        aioobe.printStackTrace();
                    }
                } else {
                    correctness[i] = true;
                }
            }
            i++;
        }
        return correctness;
    } else {
        return null;
    }
}

我查看了有关代码审查和堆栈溢出的其他问题，例如：

Calling remove in foreach loop in Java Removing object from ArrayList in for each loop 在迭代列表时删除列表中的元素 我将不胜感激任何帮助。谢谢！

Answer 1

Arrays.asList 版本是不可变的，这就是它抛出UnsupportedOperationException 的确切原因。

如 java 文档所述：

Arrays.asList 返回一个由指定数组支持的固定大小列表。

这只是意味着您不能修改列表。

解决方案：

List<String> c1 = new ArrayList<>(Arrays.asList(code1.replace("-1.0,", "")
.replace("null", "").split(",")));

List<String> c2 = new ArrayList<>(Arrays.asList(code2.replace("-1.0,", "")
.replace("null", "").split(",")));

Answer 2

使用 ArrayList 因为它支持通过迭代删除

List<String> c1 = new ArrayList<>(Arrays.asList(code1.replace("-1.0,", "").replace("null", "").split(",")));
List<String> c2 = new ArrayList<>(Arrays.asList(code2.replace("-1.0,", "").replace("null", "").split(",")));