JCH
Java Community | Help. Code. Learn.•9mo ago
Steadhaven

CopyOnWriteArrayList iterator behaviour?

package org.example;
import java.util.*;
import java.util.concurrent.CopyOnWriteArrayList;

public class CopyOnWriteArrayListExamples {
    public static void main(String[] args) {
        List<String> names = new CopyOnWriteArrayList<>(
                Arrays.asList("John", "Anton","Heinz")
        );
        for (Iterator<String> it = names.iterator(); it.hasNext(); ) {
            String name =  it.next();
            System.out.println("Checking: " + name);
            if (name.contains("o")) names.remove(name);
        }
        System.out.println("names = " + names);
    }
}
package org.example;
import java.util.*;
import java.util.concurrent.CopyOnWriteArrayList;

public class CopyOnWriteArrayListExamples {
    public static void main(String[] args) {
        List<String> names = new CopyOnWriteArrayList<>(
                Arrays.asList("John", "Anton","Heinz")
        );
        for (Iterator<String> it = names.iterator(); it.hasNext(); ) {
            String name =  it.next();
            System.out.println("Checking: " + name);
            if (name.contains("o")) names.remove(name);
        }
        System.out.println("names = " + names);
    }
}
It seems that if you create an Iterator on CopyOnWriteArrayList, then they initially point to the same Array object (@786 in this case). But as you continue iterating through it and, say, remove an element, then the CopyOnWriteArrayList becomes a new instance (now pointing to @785) with the element removed, whereas the Iterator still keeps the old Array (@786). If I understand it correctly, then this is why CopyOnWriteArrayList allows modification as you iterate through its collection, whereas normally its not possible due to potential errors happening (skipping over elements as you delete). Am I right?
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JavaBot
JavaBot•9mo ago
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