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public abstract class ConcurrentModificationProblem implements ConcurrentModificationSolvable {

    public final ArrayList<String> experimentData() {
        ArrayList<String> roundList = new ArrayList<>();
        roundList.add("A");
        roundList.add("B");
        roundList.add("C");
        roundList.add("D");
        return roundList;
    }

ThanawatMas

public abstract class ConcurrentModificationSolution extends ConcurrentModificationProblem {

    final void solve() {
        ArrayList<String> roundList = experimentData();
        String newItem = "C";

        System.out.println("**************************   Solve by " + solutionName());
        System.out.println("Before : " + roundList);
        try {
            long start = System.currentTimeMillis();

ThanawatMas

public class SolveByCopyOnWriteArrayList extends ConcurrentModificationSolution {

    @Override
    public void addItemAndReIndex(List<String> roundItem, String newItem) {
        List<String> copyRoundItem = new CopyOnWriteArrayList<>(roundItem);
        for(String item: copyRoundItem) {
            if(item.equals(newItem)) {
                roundItem.remove(item);
            }
        }

ThanawatMas

public class SolveByCopyToRemove extends ConcurrentModificationSolution {

    @Override
    public void addItemAndReIndex(List<String> roundList, String newItem) {
        ArrayList<String> copy = new ArrayList<>();
        for (String item : roundList) {
            if (item.equals(newItem)) {
                copy.add(item);
            }
        }

ThanawatMas

public class SolveByInnosense extends ConcurrentModificationSolution {

    @Override
    public void addItemAndReIndex(List<String> roundList, String newItem) {
        for (String item : roundList) {
            if (item.equals(newItem)) {
                roundList.remove(item);
                roundList.add(0, newItem);
            }
        }

ThanawatMas

public class SolveBySomeSense extends ConcurrentModificationSolution {

    @Override
    public void addItemAndReIndex(List<String> roundList, String newItem) {
        for (String item : roundList) {
            if (item.equals(newItem)) {
                roundList.remove(item);
                roundList.add(0, newItem);
                break;
            }

ThanawatMas

public class SolveByIterator extends ConcurrentModificationSolution {

    @Override
    public void addItemAndReIndex(List<String> roundItem, String newItem) {
        Iterator iterator = roundItem.iterator();
        while(iterator.hasNext()) {
            String item = (String) iterator.next();
            if(item.equals(newItem)) {
                iterator.remove();
                break;

ThanawatMas

public class SolveByJava8RemoveIf extends ConcurrentModificationSolution {

    @Override
    public void addItemAndReIndex(List<String> roundList, String newItem) {
        roundList.removeIf(item -> item.equals(newItem));
        roundList.add(0, newItem);
    }

    @Override
    public String solutionName() {

ThanawatMas

import static java.util.stream.Collectors.toList;

public class SolveByJava8Stream extends ConcurrentModificationSolution {

    @Override
    public void addItemAndReIndex(List<String> roundList, String newItem) {
        roundList = roundList
                .stream()
                .filter(item -> !item.equals(newItem))
                .map(Object::toString)

ThanawatMas

import static java.util.stream.Collectors.toList;

public class SolveByJava8Stream extends ConcurrentModificationSolution {

    @Override
    public void addItemAndReIndex(List<String> roundList, String newItem) {
        System.out.println("Before roundListIdentity=" + System.identityHashCode(roundList));
        roundList = roundList
                .stream()
                .filter(item -> !item.equals(newItem))