Collections synchronizedList() method in Java with Examples

Last Updated : 18 Jul, 2026

The Collections.synchronizedList() method of the java.util.Collections class returns a thread-safe (synchronized) view of the specified list. It wraps an existing List and synchronizes all its methods, making it safe for concurrent access by multiple threads.

  • Supports all List implementations such as ArrayList and LinkedList.
  • Iteration must be manually synchronized.

Syntax

public static <T> List<T> synchronizedList(List<T> list)

Parameter

  • list –> The list to be wrapped in a synchronized (thread-safe) list.

Return Value: Returns a synchronized (thread-safe) view of the specified list.

Example: Creating a Synchronized List of Strings

Java 
import java.util.*;

public class GFG1 {
    public static void main(String[] argv) throws Exception
    {
        try {

            // creating object of List<String>
            List<String> list = new ArrayList<String>();

            // populate the list
            list.add("A");
            list.add("B");
            list.add("C");
            list.add("D");
            list.add("E");

            // printing the Collection
            System.out.println("List : " + list);

            // create a synchronized list
            List<String> synlist = Collections
                                       .synchronizedList(list);

            // printing the Collection
            System.out.println("Synchronized list is : " + synlist);
        }

        catch (IllegalArgumentException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

Output
List : [A, B, C, D, E]
Synchronized list is : [A, B, C, D, E]

Explanation: The ArrayList is wrapped using Collections.synchronizedList(). The returned list synchronizes all operations, allowing multiple threads to access it safely.

Example: Creating a Synchronized List of Integers

Java 
import java.util.*;

public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {

        try {

            // creating object of List<Integer>
            List<Integer> list = new ArrayList<Integer>();

            // populate the list
            list.add(20);
            list.add(30);
            list.add(40);
            list.add(50);
            list.add(60);

            // printing the Collection
            System.out.println("List : " + list);

            // create a synchronized list
            List<Integer> synlist = Collections
                                        .synchronizedList(list);

            // printing the Collection
            System.out.println("Synchronized list is : " + synlist);
        }

        catch (IllegalArgumentException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

Output
List : [20, 30, 40, 50, 60]
Synchronized list is : [20, 30, 40, 50, 60]

Explanation: The integer list is converted into a synchronized list. Any access to the returned list is synchronized internally, making it suitable for multi-threaded applications.

Iterating Over a Synchronized List

Although the list is synchronized, iteration must still be synchronized manually to avoid unexpected behavior.

Java 
import java.util.*;

public class GFG {

    public static void main(String[] args) {

        List<String> list = Collections.synchronizedList(new ArrayList<>());

        list.add("Java");
        list.add("Python");
        list.add("C++");

        synchronized (list) {
            for (String s : list) {
                System.out.println(s);
            }
        }
    }
}

Output
Java
Python
C++

Explanation: The synchronized block ensures that no other thread modifies the list while it is being traversed.

Advantages of synchronizedList()

  • Provides thread-safe access to a list.
  • Prevents data inconsistency during concurrent access.
  • Works with any List implementation.
  • Easy to convert an existing list into a synchronized list.
  • Does not require creating a new list.

Limitations

  • Iteration requires manual synchronization.
  • Synchronization introduces performance overhead.
  • Less scalable than concurrent collections like CopyOnWriteArrayList.
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