What is Java Synchronized Collections? Complete Tutorials using java.util.Collections

Java Collection Framework is one of the most used section. There are more than 100 APIs are available for us to use at fingertips.

synchronizedMap() returns a synchronized (thread-safe) map backed by the specified map and we will use one more API synchronizedList().

If you have any of below questions then you are at right place:

• Get Synchronized List from ArrayList example
• How do I synchronize a collection?
• How do I synchronize a List or other Collection in Java
• Collections.synchronizedList and synchronized
• java.util.Collections.synchronizedMap() Method Example
• Java Thread Synchronization Tutorial

In this Java example I’ll show how to Synchronized Map and List. We will be using synchronizedMap() method is used to return a synchronized (thread-safe) map backed by the specified map and the same way synchronizedList().

Let’s use List in description. The Collections class provides us with synchronizedList(List list) API method, that returns a synchronized (thread-safe) list from the provided ArrayList.

Here are the detailed Steps:

• Create an ArrayList
• Populate the arrayList with elements, with add(E e) API method of ArrayList
• Invoke the synchronizedList(List list) API method of Collections to get the synchronized list from the provided ArrayList

Let’s take a look at the code snippet:

package com.crunchify.tutorials;

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/**
 * @author Crunchify.com
 * 
 */

public class CrunchifySynchronizedListFromArrayList {

    public static void main(String[] args) {

        // ********************** synchronizedList ************************
        ArrayList<String> crunchifyArrayList = new ArrayList<String>();

        // populate the crunchifyArrayList
        crunchifyArrayList.add("eBay");
        crunchifyArrayList.add("Paypal");
        crunchifyArrayList.add("Google");
        crunchifyArrayList.add("Yahoo");

        // Returns a synchronized (thread-safe) list backed by the specified
        // list. In order to guarantee serial access, it is critical that all
        // access to the backing list is accomplished through the returned list.
        List<String> synchronizedList = Collections.synchronizedList(crunchifyArrayList);

        System.out.println("synchronizedList conatins : " + synchronizedList);

        // ********************** synchronizedMap ************************
        Map<String, String> crunchifyMap = new HashMap<String, String>();

        // populate the crunchifyMap
        crunchifyMap.put("1", "eBay");
        crunchifyMap.put("2", "Paypal");
        crunchifyMap.put("3", "Google");
        crunchifyMap.put("4", "Yahoo");

        // create a synchronized map
        Map<String, String> synchronizedMap = Collections.synchronizedMap(crunchifyMap);

        System.out.println("synchronizedMap contains : " + synchronizedMap);
    }
}

Eclipse Console Result:

synchronizedList conatins : [eBay, Paypal, Google, Yahoo]
synchronizedMap contains : {3=Google, 2=Paypal, 1=eBay, 4=Yahoo}