Java TreeSet first() Method

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Description

The Java TreeSet first() method is used to return the first (lowest) element currently in this set.

Declaration

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

public E first()

Parameters

NA

Return Value

The method call returns the first (lowest) element currently in this set.

Exception

NoSuchElementException − This exception is thrown if the set is empty.

Getting First Entry from the TreeSet of Integer Example

The following example shows the usage of Java TreeSet first() method to get the first/lowest entry in the treeset. We've created a TreeSet object of Integer. Then few entries are added using add() method to the set. Using first() method, we've received the lowest value and printed it.

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(11);
      treeset.add(16);
      treeset.add(15);

      // getting the first lowset element
      System.out.println("First lowest element: "+treeset.first());   
   }    
}  

Output

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

First lowest element: 11

Getting First Entry from the TreeSet of String Example

The following example shows the usage of Java TreeSet first() method to get the first/lowest entry in the treeset. We've created a TreeSet object of String. Then few entries are added using add() method to the set. Using first() method, we've received the lowest value and printed it.

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("D");
      treeset.add("A");
      treeset.add("C");
      treeset.add("B");

      // getting the first lowset element
      System.out.println("First lowest element: "+treeset.first());   
   }    
}  

Output

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

First lowest element: A

Getting First Entry from the TreeSet of Object Example

The following example shows the usage of Java TreeSet first() method to get the first/lowest entry in the treeset. We've created a TreeSet object of Student objects. Then few entries are added using add() method to the set. Using first() method, we've received the lowest value and printed it.

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

      // getting the first lowset element
      System.out.println("First lowest element: "+treeset.first());   
   }    
}  
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.

First lowest element: [ 1, Robert ]