Java LinkedList contains() Method

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Description

The Java LinkedList contains(Object) method returns true if this list contains the specified element. The object should have implemented equals() method in order to make this operation successful.

Declaration

Following is the declaration for java.util.LinkedList.contains() method

public boolean contains(Object o)

Parameters

o − The element whose presence in this list is to be tested.

Return Value

This method returns true if this list contains the specified element.

Exception

NA

Checking Existence of an Element in a LinkedList of Integers Example

The following example shows the usage of Java LinkedList contains() method. We're using Integers. We'll be adding few elements and then checking if certain element is present or not.

package com.tutorialspoint;

import java.util.LinkedList;

public class LinkedListDemo {
   public static void main(String[] args) {

      // create an empty linkedList
      LinkedList<Integer> linkedList = new LinkedList<>();

      // use add() method to add elements in the linkedList
      linkedList.add(20);
      linkedList.add(30);
      linkedList.add(10);
      linkedList.add(18);        

      // let us print all the elements available in linkedList
      System.out.println("LinkedList = " + linkedList);

      // linkedList contains element 10
      if (linkedList.contains(10)) {
         System.out.println("element 10 is present in the linkedList");
      } else {
         System.out.println("element 10 is not present in the linkedList");
      }

      // linkedList does not contain element 25
      if (linkedList.contains(25)) {
         System.out.println("element 25 is present in the linkedList");
      } else {
         System.out.println("element 25 is not present in the linkedList");    
      }
   }
}           

Output

Let us compile and run the above program, this will produce the following result −

LinkedList = [20, 30, 10, 18]
element 10 is present in the linkedList
element 25 is not present in the linkedList

Checking Existence of an Element in a LinkedList of Strings Example

The following example shows the usage of Java LinkedList contains() method with Strings. We'll be adding few elements and then checking if certain element is present or not.

package com.tutorialspoint;

import java.util.LinkedList;

public class LinkedListDemo {
   public static void main(String[] args) {

      // create an empty linkedList
      LinkedList<String> linkedList = new LinkedList<>();

      // use add() method to add elements in the linkedList
      linkedList.add("Welcome");
      linkedList.add("to");
      linkedList.add("tutorialspoint");
      linkedList.add(".com");        

      // let us print all the elements available in linkedList
      System.out.println("LinkedList = " + linkedList);

      // linkedList contains element tutorialspoint
      if (linkedList.contains("tutorialspoint")) {
         System.out.println("element tutorialspoint is present in the linkedList");
      } else {
         System.out.println("element tutorialspoint is not present in the linkedList");
      }

      // linkedList does not contain element html
      if (linkedList.contains("html")) {
         System.out.println("element html is present in the linkedList");
      } else {
         System.out.println("element html is not present in the linkedList");    
      }
   }
}           

Output

Let us compile and run the above program, this will produce the following result −

LinkedList = [Welcome, to, tutorialspoint, .com]
element tutorialspoint is present in the deque
element html is not present in the deque

Checking Existence of an Element in a LinkedList of Objects Example

The following example shows the usage of Java LinkedList contains() method with Student objects. We'll be adding few elements and then checking if certain element is present or not.

package com.tutorialspoint;

import java.util.LinkedList;

public class LinkedListDemo {
   public static void main(String[] args) {

      // create an empty linkedList
      LinkedList<Student> linkedList = new LinkedList<>();

      // use add() method to add elements in the linkedList
      linkedList.add(new Student(1, "Julie"));
      linkedList.add(new Student(2, "Robert"));
      linkedList.add(new Student(3, "Adam"));      

      // let us print all the elements available in linkedList
      System.out.println("LinkedList = " + linkedList);

      // linkedList contains element Robert
      if (linkedList.contains(new Student(2, "Robert"))) {
         System.out.println("Student Robert is present in the linkedList");
      } else {
         System.out.println("Student Robert is not present in the linkedList");
      }

      // linkedList does not contain element Jane
      if (linkedList.contains(new Student(4, "Jane"))) {
         System.out.println("Student Jane is present in the linkedList");
      } else {
         System.out.println("Student Jane is not present in the linkedList");    
      }
   }
} 
class Student {
   int rollNo;
   String name;

   Student(int rollNo, String name){
      this.rollNo = rollNo;
      this.name = name;
   }

   @Override
   public String toString() {
      return "[ " + this.rollNo + ", " + this.name + " ]";
   }
   
   @Override
   public boolean equals(Object obj) {
      Student s = (Student)obj;
      return this.rollNo == s.rollNo && this.name.equalsIgnoreCase(s.name);
   }
}

Output

Let us compile and run the above program, this will produce the following result −

LinkedList = [[ 1, Julie ], [ 2, Robert ], [ 3, Adam ]]
Student Robert is present in the deque
Student Jane is not present in the deque