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contains method

What is CopyOnWriteArrayList.contains method() in Java?


What is CopyOnWriteArrayList?

  • The CopyOnWriteArrayList is a thread-safe implementation of ArrayList without the requirement for synchronization.
  • The whole content of the CopyOnWriteArrayList is duplicated onto a new internal copy when we use any of the altering methods, such as add() or delete(). Hence, the list can be iterated in a safe way during the modification of the list concurrently.
  • The data structure’s properties make it particularly helpful in situations when we iterate it more frequently as compared to when we alter it.
  • If adding items is a typical activity, CopyOnWriteArrayList isn’t the appropriate data structure to use, as the extra copies will almost always result in poor performance.

What is the contains() method?

contains() is an instance method of the CopyOnWriteArrayList that is used to check whether the list contains the given element or not.

The contains() method is defined in the CopyOnWriteArrayList class. The CopyOnWriteArrayList class is defined in the java.util.concurrent package. To import the CopyOnWriteArrayList class, check the following import statement.

import java.util.concurrent.CopyOnWriteArrayList;


public boolean contains(Object o)


  • Object o: This is the object to check.

Return value

This method returns true if the list contains the given object. Otherwise, it returns false.


import java.util.concurrent.CopyOnWriteArrayList;

public class Main{

    public static void main(String[] args) {
        // Create the CopyOnWriteArrayList object
        CopyOnWriteArrayList<String> copyOnWriteArrayList = new CopyOnWriteArrayList<>();

        // add elements to the end of the copyOnWriteArrayList

        // add element at the specified index
        int index = 1;
        copyOnWriteArrayList.add(index, "educative");

        // Object to check
        String stringToCheck = "hello";

        // check if the stringToCheck is present in stringToCheck
        System.out.printf("%s.contains(%s) = %s ", copyOnWriteArrayList, stringToCheck, copyOnWriteArrayList.contains(stringToCheck));
Example for CopyOnWriteArrayList.contains() method


  • Line 1: We import the CopyOnWriteArrayList class.

  • Line 7: We create an object of CopyOnWriteArrayList with the name copyOnWriteArrayList.

  • Lines 10-11: We add elements to the end of copyOnWriteArrayList.

  • Line 14: We define the index at which we want to insert the element.

  • Line 15: We pass the index defined in line 14 and the element to be inserted as arguments in the add() method.

  • Line 18: We assign the value hello to the string stringToCheck.

  • Line 21: We check whether the list contains the element using the contains() method and print the result to the console.


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