How do you check if an element is present in a list in Java?

JavaObject Oriented ProgrammingProgramming

Elements can be checked from a list using indexOf() or contains() methods.

Syntax - indexOf() method

int indexOf(Object o)

Returns the index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element. More formally, returns the lowest index i such that (o==null ? get(i)==null : o.equals(get(i))), or -1 if there is no such index.

Parameters

  • o − Element to search for.

Returns

The index of the first occurrence of the specified element in this list, or -1 if this list does not contain the element.

Throws

  • ClassCastException − If the type of the specified element is incompatible with this list (optional).

  • NullPointerException − If the specified element is null and this list does not permit null elements (optional).

Syntax - contains() method

boolean contains(Object o)

Returns true if this list contains the specified element. More formally, returns true if and only if this list contains at least one element e such that (o==null ? e==null : o.equals(e)).

Parameters

  • o − Element whose presence in this list is to be tested.

Returns

True if this list contains the specified element.

Throws

  • ClassCastException − If the type of the specified element is incompatible with this list (optional).

  • NullPointerException − If the specified element is null and this list does not permit null elements (optional).

Example

Following is the example finding elements from a list using various methods −

package com.tutorialspoint;

import java.util.ArrayList;
import java.util.List;

public class CollectionsDemo {
   public static void main(String[] args) {
      List<String> list = new ArrayList<>();
      list.add("Zara");
      list.add("Mahnaz");
      list.add("Ayan");
      System.out.println("List: " + list);
      System.out.println("Ayan is present: " + list.contains("Ayan"));
      int index = list.indexOf("Ayan");
      System.out.println("Ayan is present at: " + index);
   }
}

Output

This will produce the following result −

List: [Zara, Mahnaz, Ayan]
Ayan is present: true
Ayan is present at: 2
raja
Updated on 10-May-2022 07:40:10

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