Java HashSet contains() Method

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Description

The Java HashSet contains(Object o) method is used to return 'true' if this set contains the specified element.

Declaration

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

public boolean contains(Object o)

Parameters

o − This is the element whose presence in this set is to be tested.

Return Value

The method call returns 'true' if this set contains the specified element.

Exception

NA

Checking if HashSet of Integers Contains an Entry or Not

The following example shows the usage of Java HashSet contains() method to check entries to be present in a HashSet. We've created a HashSet object of Integer. Then few entries are added using add() method and then set is printed. An existing entry is checked using contains() method and then a non-existing entry is checked and results are printed.

package com.tutorialspoint;

import java.util.HashSet;

public class HashSetDemo {
   public static void main(String args[]) {
      
      // create hash set
      HashSet <Integer> newset = new HashSet <>();

      // populate hash set
      newset.add(1); 
      newset.add(2);
      newset.add(3);  
	  
      // print the set	  
      System.out.println("Hash set: "+ newset);
	  
      // checking elements in hash set
      System.out.println("Hash set contains 1: "+ newset.contains(1));
      System.out.println("Hash set contains 4: "+ newset.contains(4));
      
   }    
}

Output

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

Hash set: [1, 2, 3]
Hash set contains 1: true
Hash set contains 4: false

Checking if HashSet of Strings Contains an Entry or Not

The following example shows the usage of Java HashSet contains() method to check entries to be present in a HashSet. We've created a HashSet object of Strings. Then few entries are added using add() method and then set is printed. An existing entry is checked using contains() method and then a non-existing entry is checked and results are printed.

package com.tutorialspoint;

import java.util.HashSet;

public class HashSetDemo {
   public static void main(String args[]) {
      
      // create hash set
      HashSet <String> newset = new HashSet <>();

      // populate hash set
      newset.add("Learning"); 
      newset.add("Easy");
      newset.add("Simply");  

      // print the set	  
      System.out.println("Hash set: "+ newset);
	  
      // checking elements in hash set
      System.out.println("Hash set contains - Easy: "+ newset.contains("Easy"));
      System.out.println("Hash set contains - Tutorials: "+ newset.contains("Tutorials"));
   }    
}

Output

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

Hash set: [Learning, Easy, Simply]
Hash set contains - Easy: true
Hash set contains - Tutorials: false

Checking if HashSet of Objects Contains an Entry or Not

The following example shows the usage of Java HashSet contains() method to check entries to be present in a HashSet. We've created a HashSet object of Student objects. Then few entries are added using add() method and then set is printed. An existing entry is checked using contains() method and then a non-existing entry is checked and results are printed.

package com.tutorialspoint;

import java.util.HashSet;

public class HashSetDemo {
   public static void main(String args[]) {
      
      // create hash set
      HashSet <Student> newset = new HashSet <>();

      // populate hash set
      newset.add(new Student(1, "Julie")); 
      newset.add(new Student(2, "Robert"));
      newset.add(new Student(3, "Adam"));	  

      // print the set	  
      System.out.println("Hash set: "+ newset);
	  
      // checking elements in hash set
      System.out.println("Hash set contains - Julie: "+ newset.contains(new Student(1, "Julie")));
      System.out.println("Hash set contains - Jene: "+ newset.contains(new Student(4, "Jene")));
   }    
}
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) {
      if(obj == null) return false;
      Student s = (Student)obj;
      return this.rollNo == s.rollNo && this.name.equalsIgnoreCase(s.name);
   }
   @Override
   public int hashCode() {
      return rollNo + name.hashCode();
   }
}

Output

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

Hash set: [[ 2, Robert ], [ 1, Julie ], [ 3, Adam ]]
Hash set contains - Julie: true
Hash set contains - Jene: false