Java TreeSet contains() Method

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Description

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

Declaration

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

public boolean contains(Object o)

Parameters

o − This is the object to be checked for containment in this set.

Return Value

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

Exception

• ClassCastException − This is thrown if the specified element cannot be compared with the elements currently exists in the set.

• NullPointerException − This is thrown if the specified element is null and this set uses natural ordering, or its comparator does not permit null elements.

Checking an Element's Presence in a TreeSet of Integer Example

The following example shows the usage of Java TreeSet contains() method to check if an element is present in the treeset. We've created a TreeSet object of Integer. Then few entries are added using add() method and an element is checked in the set and result is printed.

package com.tutorialspoint;

import java.util.TreeSet;

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

      // creating a TreeSet 
      TreeSet <Integer>treeset = new TreeSet<>();

      // adding in the tree set
      treeset.add(12);
      treeset.add(13);
      treeset.add(14);
      treeset.add(15);

      // check existence of 15  
      System.out.println("Checking existence of 15 ");
      System.out.println("Is 15 there in the set: "+treeset.contains(15));
   }    
}

Output

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

Checking existence of 15 
Is 15 there in the set: true

Checking an Element's Presence in a TreeSet of String Example

The following example shows the usage of Java TreeSet contains() method to check if an element is present in the treeset. We've created a TreeSet object of String. Then few entries are added using add() method and an element is checked in the set and result is printed.

package com.tutorialspoint;

import java.util.TreeSet;

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

      // creating a TreeSet 
      TreeSet <String>treeset = new TreeSet<>();

      // adding in the tree set
      treeset.add("12");
      treeset.add("13");
      treeset.add("14");
      treeset.add("15");

      // check existence of "15"  
      System.out.println("Checking existence of 15 ");
      System.out.println("Is 15 there in the set: "+treeset.contains("15"));
   }    
}

Output

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

Checking existence of 15 
Is 15 there in the set: true

Checking an Element's Presence in a TreeSet of Object Example

The following example shows the usage of Java TreeSet contains() method to check if an element is present in the treeset. We've created a TreeSet object of Student objects. Then few entries are added using add() method and an element is checked in the set and result is printed.

package com.tutorialspoint;

import java.util.TreeSet;

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

      // creating a TreeSet 
      TreeSet <Student>treeset = new TreeSet<>();

      // adding in the tree set
      treeset.add(new Student(1, "Robert"));
      treeset.add(new Student(2, "Julie"));
      treeset.add(new Student(3, "Adam"));
      treeset.add(new Student(4, "Julia"));

      // check existence of "Adam"  
      System.out.println("Checking existence of 15 ");
      System.out.println("Is Adam there in the set: "+treeset.contains(new Student(3, "Adam")));
   }    
}
class Student implements Comparable<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);
   }

   @Override
   public int compareTo(Student student) {
      return this.rollNo - student.rollNo;
   }
}

Output

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

Checking existence of 15 
Is Adam there in the set: true