An ArrayList is a subclass of AbstractList class and it can be used to store a dynamically sized collection of elements. An ArrayList grows its size to accommodate new elements and shrinks the size when the elements are removed, so it is called resizable or dynamic array. An ArrayList can allow duplicates and null values.
There are two ways to synchronize an ArrayList in Java
Collections.synchronizedList() method
The synchronizedList() method is used to synchronize the collections in Java.
Syntax
public static List<T> synchronizedList(List<T> list)
Example
import java.util.*;
public class SynchronizedListTest {
public static void main(String[] args) {
List<String> list = new ArrayList<String>();
list.add("IND");
list.add("AUS");
list.add("WI");
list.add("NZ");
list.add("ENG");
List<String> synlist = Collections.synchronizedList(list);
synchronized(synlist) {
Iterator<String> itr = synlist.iterator();
while(itr.hasNext()) {
String str = itr.next();
System.out.println(str);
}
}
}
}Output
IND AUS WI NZ ENG
CopyOnWriteArrayList
The CopyOnWriteArrayList will create a list of the elements in the order of specified collection. It is thread-safe concurrent access of ArrayList. When an ArrayList is modified, it will create a fresh copy of the underlying array.
Syntax
public class CopyOnWriteArrayList<E> extends Object implements List<E>, RandomAccess, Cloneable, Serializable
Example
import java.util.*;
import java.util.concurrent.*;
public class CopyOnWriteArrayListTest {
public static void main(String[] args) {
CopyOnWriteArrayList list = new CopyOnWriteArrayList();
list.add("Java");
list.add("Scala");
list.add("Python");
list.add("Selenium");
list.add("ServiceNow");
System.out.println("Displaying synchronized ArrayList: ");
Iterator itr = list.iterator();
while(itr.hasNext()) {
String str = itr.next();
System.out.println(str);
}
}
}Output
Displaying synchronized ArrayList: Java Scala Python Selenium ServiceNow