How can I remove an item from a list while iterating over it?

Question

I have the following code:

while (rrProcesses.size() > 0) {
        for (Process process : rrProcesses) {
            if (process.getBurstTime() <= quantum) {
                System.out.println("@t=" + clock + ", selected for " + process.getBurstTime() + " units");
                clock += process.getBurstTime();
                rrProcesses.remove(process);
            } else {
                System.out.println("@t=" + clock + ", selected for " + quantum + " units");
                clock += quantum;
                process.setBurstTime(process.burstTime - quantum);
            }

            if (processCounter != rrProcesses.size()) {
                System.out.println("@t=" + clock + ", context switch " + contextSwitch + " occurs");
                contextSwitch++;
                clock += latency;
            }
        }
    }

I am attempting to iterate over each object within my list, remove an item based on a conditional, and keep looping until all items are removed.

When I run this in intellij, I get the following err:

Exception in thread "main" java.util.ConcurrentModificationException
at java.base/java.util.ArrayList$Itr.checkForComodification(ArrayList.java:1013)
at java.base/java.util.ArrayList$Itr.next(ArrayList.java:967)
at com.company.Main.main(Main.java:224)

I searched the issue and found this solution. enter link description here

When I changed my code it became this:

Iterator<Process> iter = rrProcesses.iterator();

    while (iter.hasNext()) {
        for (Process process : rrProcesses) {
            if (process.getBurstTime() <= quantum) {
                System.out.println("@t=" + clock + ", selected for " + process.getBurstTime() + " units");
                clock += process.getBurstTime();
                iter.remove();
            } else {
                System.out.println("@t=" + clock + ", selected for " + quantum + " units");
                clock += quantum;
                process.setBurstTime(process.burstTime - quantum);
            }

            if (processCounter != rrProcesses.size()) {
                System.out.println("@t=" + clock + ", context switch " + contextSwitch + " occurs");
                contextSwitch++;
                clock += latency;
            }
        }
    }

However, now I am receiving the following error:

Exception in thread "main" java.lang.IllegalStateException
at java.base/java.util.ArrayList$Itr.remove(ArrayList.java:980)
at com.company.Main.main(Main.java:228)

I found this answer to the error but its honestly not clarifying anything for me. How is it possible for me to then remove the object from the List?

score 3 · Accepted Answer · answered Mar 23 '22 at 03:59

3

You still have a for loop inside your iterator loop. Replace it with this:

Process process = iter.next();

answered Mar 23 '22 at 03:59

shmosel

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Thank you, will check it when the timer clears. – DougM Mar 23 '22 at 04:02

score 2 · Answer 2 · answered Mar 23 '22 at 04:27

Alternative to @shmosel s answer, you can also use a for loop that iterates over the iterator. With this, you can also remove the item in question.

Basically this is the same approach as yours (get iter, while iter.hasNext, iter.next) but I prefer this style, because it keeps all allocated variables inside the loop scope.

    for (final Iterator<Processes> iter = rrProcesses.iterator(); iter.hasNext();) {
        System.out.println("\t" + iter.next());
    }

How can I remove an item from a list while iterating over it?

2 Answers2