Java TreeSet add() Method

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Description

The Java TreeSet add(Object o) method is used to add the specified element to this set if it is not already present.

Declaration

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

public boolean add(Object o)

Parameters

o − This is the element to be added to this set.

Return Value

The method call returns true if the set did not already contain the specified element.

Exception

ClassCastException − It throws the exception if the specified object cannot be compared with the elements currently in the set.

Adding an Entry to a TreeSet of Integer Example

The following example shows the usage of Java TreeSet add() method to add entries to the treeset. We've created a TreeSet object of Integer. Then few entries are added using add() method and treeset object is printed to check its content.

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);

      // displaying the Tree set data
      System.out.print("Tree set : " + treeset);
   }   
}

Output

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

Tree set : [12, 13, 14, 15]

Adding an Entry to a TreeSet of String Example

The following example shows the usage of Java TreeSet add() method to add entries to the treeset. We've created a TreeSet object of String. Then few entries are added using add() method and treeset object is printed to check its content.

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");

      // displaying the Tree set data
      System.out.print("Tree set : " + treeset);
   }   
}

Output

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

Tree set : [12, 13, 14, 15]

Adding an Entry to a TreeSet of Object Example

The following example shows the usage of Java TreeSet add() method to add entries to the treeset. We've created a TreeSet object of Student objects. Then few entries are added using add() method and treeset object is printed to check its content.

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(new Student(1, "Robert"));
      treeset.add(new Student(2, "Julie"));
      treeset.add(new Student(3, "Adam"));
      treeset.add(new Student(4, "Julia"));

      // displaying the Tree set data
      System.out.print("Tree set : " + treeset);
   }   
}
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.

Tree set : [[ 1, Robert ], [ 2, Julie ], [ 3, Adam ], [ 4, Julia ]]