Comparing data numbers, Iterator.remove() throwing NullPointerException

Question

I am trying to make an Android app that can compare integers. However, when I am trying to compare integers and I need to delete some entries because they are redundant or they do not fit in, I cannot use Iterator.remove() without encountering a NullPointerException. Here is the specific output:

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)

Here is the code region(at com.daita.musicale.MainActivity.checkNotes(MainActivity.java:115)) that is giving me the error.

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;
    }
}

I have looked at other questions on both Code Review and Stack Overflow, for example:

Calling remove in foreach loop in Java Removing object from ArrayList in for each loop Removing elements on a List while iterating through it I would greatly appreciate any help. Thank you!

Ousmane D. · Accepted Answer · 2017-05-06T16:25:44.093

The Arrays.asList version is immutable, that's the exact reason why it's throwing an UnsupportedOperationException.

as stated by java docs:

Arrays.asList returns a fixed-size list backed by the specified array.

that simply means you cannot modify the list.

Solution:

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(",")));

score 0 · Answer 2 · answered May 06 '17 at 13:07

0

Use an ArrayList because it supports removal with iterating

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(",")));

answered May 06 '17 at 13:07

berrytchaks

839
10
18

This is an equally good answer, @berrytchaks, just that I saw and used the other one first. – May 06 '17 at 13:08
Glad that you got unstuck even though it is was not because of my solution ;) – berrytchaks May 06 '17 at 13:12

Comparing data numbers, Iterator.remove() throwing NullPointerException

2 Answers2