Which method is used by the Contains method of a list to search an element?

List contains() method in Java with Examples

The contains() method of List interface in Java is used for checking if the specified element exists in the given list or not.

Table of Contents Show

List contains() method in Java with Examples
What is the ArrayList.contains() method in Java?
1. Overview
Java ArrayList.contains() Method
public boolean contains(Object o)
1. ArrayList contains() syntax

Syntax:

public boolean contains(Object obj) object-element to be searched for

Parameters: This method accepts a single parameter obj whose presence in this list is to be tested.

Return Value: It returns true if the specified element is found in the list else it returns false.

Below programs illustrate the contains() method in List:

Program 1: Demonstrate the working of the method contains() in List of integer.

// Java code to demonstrate the working of 
// contains() method in List interface 

import java.util.*;

class GFG {

public static void main(String[] args)

{

// creating an Empty Integer List

List<Integer> arr = new ArrayList<Integer>(4);

// using add() to initialize values

// [1, 2, 3, 4]

arr.add(1);

arr.add(2);

arr.add(3);

arr.add(4);

// use contains() to check if the element

// 2 exits or not

boolean ans = arr.contains(2);

if (ans)

System.out.println("The list contains 2");

else

System.out.println("The list does not contains 2");

// use contains() to check if the element

// 5 exits or not

ans = arr.contains(5);

if (ans)

System.out.println("The list contains 5");

else

System.out.println("The list does not contains 5");

}
}

Output: The list contains 2 The list does not contains 5

Program 2: Demonstrate the working of the method contains() in List of string.

// Java code to demonstrate the working of 
// contains() method in List of string 

import java.util.*;

class GFG {

public static void main(String[] args)

{

// creating an Empty String List

List<String> arr = new ArrayList<String>(4);

// using add() to initialize values

// ["geeks", "for", "geeks"]

arr.add("geeks");

arr.add("for");

arr.add("geeks");

// use contains() to check if the element

// "geeks" exits or not

boolean ans = arr.contains("geeks");

if (ans)

System.out.println("The list contains geeks");

else

System.out.println("The list does not contains geeks");

// use contains() to check if the element

// "coding" exits or not

ans = arr.contains("coding");

if (ans)

System.out.println("The list contains coding");

else

System.out.println("The list does not contains coding");

}
}

Output: The list contains geeks The list does not contains coding

Practical Application: In search operations, we can check if a given element exists in a list or not.

Reference: https://docs.oracle.com/javase/7/docs/api/java/util/List.html#contains(java.lang.Object)

Article Tags :

Java

Java-Collections

Java-Functions

java-list

Practice Tags :

Java

Java-Collections

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What is the ArrayList.contains() method in Java?

The ArrayList.contains() method in Java is used to check whether or not a list contains a specific element.

To check if an element is in an array, we first need to convert the array into an ArrayList using the asList() method and then apply the same contains() method to it.

1. Overview

Finding an element in a list is a very common task we come across as developers.

In this quick tutorial, we'll cover different ways we can do this with Java.

Java ArrayList.contains() Method

Last update on February 26 2020 08:07:31 (UTC/GMT +8 hours)

public boolean contains(Object o)

The contains() method is used to determines whether an element exists in an ArrayList object. Returns true if this list contains the specified element.

Package: java.util

Java Platform: Java SE 8

Syntax:

contains(Object o)

Parameters:

Name	Description
o	Element whose presence in this list is to be tested

Return Value:
true if this list contains the specified element

Return Value Type: boolean

Pictorial presentation of ArrayList.contains() Method

Example: ArrayList.contains Method

The following example checks whether a particular student is present in a list.

import java.util.*; public class test { public static void main(String[] args) { // ArrayList with Capacity 4 ArrayList<String> StudentList = new ArrayList<String>(4); //Added 4 elements StudentList.add("David"); StudentList.add("Tom"); StudentList.add("Rohit"); StudentList.add("Paul"); System.out.println("Students in the list are : "); System.out.println(StudentList); System.out.print("Is list contains the student Tom?"); System.out.println(StudentList.contains("Tom")); System.out.print("Is list contains the student Sudhir?"); System.out.println(StudentList.contains("Sudhir")); } }

Output:

F:\java>javac test.java F:\java>java test Students in the list are : [David, Tom, Rohit, Paul] Is list contains the student Tom?true Is list contains the student Sudhir?false

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1. ArrayList contains() syntax

The contains() method is pretty simple. It simply checks the index of element in the list. If the index is greater than '0' than element is present in the list.

public boolean contains(Object o) { return indexOf(o) >= 0; }