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Java Collections - Collections.synchronizedCollection() Examples

Java Collections Java Java API 

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Class:

java.util.Collections

java.lang.Objectjava.lang.Objectjava.util.Collectionsjava.util.CollectionsLogicBig

Method:

public static <T> Collection<T> synchronizedCollection(Collection<T> c)

Returns a synchronized (thread-safe) collection backed by the specified collection.


Examples


Without synchronizedCollection. 

package com.logicbig.example.collections;

import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

public class SynchronizedCollectionExample {

    public static void main(String... args) throws InterruptedException {

        Collection<Integer> collection = IntStream.rangeClosed(1, 10000)
                                                  .boxed()
                                                  .collect(Collectors.toList());
        System.out.println("initial size: " + collection.size());

        final ExecutorService e = Executors.newFixedThreadPool(10000);
        for (int i = 0; i < 10000; i++) {
            e.execute(() -> {
                try {
                    Integer first = collection.iterator().next();
                    collection.remove(first);
                } catch (ConcurrentModificationException e1) {
                    System.out.println(e1);
                }
            });
        }
        e.shutdown();
        e.awaitTermination(1000, TimeUnit.SECONDS);
        System.out.println(collection.size());//should be zero
    }
}

Output

initial size: 10000
java.util.ConcurrentModificationException
java.util.ConcurrentModificationException
java.util.ConcurrentModificationException
java.util.ConcurrentModificationException
java.util.ConcurrentModificationException
java.util.ConcurrentModificationException
java.util.ConcurrentModificationException
java.util.ConcurrentModificationException
17




Using synchronizedCollection 

package com.logicbig.example.collections;

import java.util.Collection;
import java.util.Collections;
import java.util.ConcurrentModificationException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.stream.Collectors;
import java.util.stream.IntStream;

public class SynchronizedCollectionExample2 {

    public static void main(String... args) throws InterruptedException {

        Collection<Integer> c = IntStream.rangeClosed(1, 10000)
                                         .boxed()
                                         .collect(Collectors.toList());
        Collection<Integer> collection = Collections.synchronizedCollection(c);
        System.out.println("initial size: " + collection.size());

        final ExecutorService e = Executors.newFixedThreadPool(10000);
        for (int i = 0; i < 10000; i++) {
            try {
                Integer first = collection.iterator().next();
                collection.remove(first);
            } catch (ConcurrentModificationException e1) {
                System.out.println(e1);
            }
        }
        e.shutdown();
        e.awaitTermination(1000, TimeUnit.SECONDS);
        System.out.println(collection.size());//should be zero
    }
}

Output

initial size: 10000
0

See Also