The Java.util.TreeSet.first() method is used to return the first of the element of a TreeSet. The first element here is being referred to the lowest of the elements in the set. If the elements are of integer types then the smallest integer is returned. If the elements are of the string types then the elements are checked in the alphabetical order and the string starting with the initial alphabets in the order of dictionary is returned irrespective of length.
Syntax:
Tree_Set.first()
Parameters: The method does not take any parameters.
Return Value: The method returns the lowest member of the set. If the elements are of string type then they are checked in alphabetical order irrespective of length and if the elements are of integer types then the smallest integer is returned. Also, the numbers of string type hold higher priority.
Below are the programs illustrating the use of Java.util.TreeSet.first() method:
Program 1: When the elements are of integer types.
// Java code to illustrate first()import java.util.*;import java.util.TreeSet;  public class TreeSetDemo {    public static void main(String args[])    {        // Creating an empty TreeSet        TreeSet<Integer> tree = new TreeSet<Integer>();          // Use add() method to add elements into the Set        tree.add(14);        tree.add(8);        tree.add(200);        tree.add(48);        tree.add(7);        tree.add(124);          // Displaying the TreeSet        System.out.println("TreeSet: " + tree);          // Displaying the lowest element of the set        System.out.println("The first element is: " + tree.first());    }} |
TreeSet: [7, 8, 14, 48, 124, 200] The first element is: 7
Program 2: When the elements are of string types.
// Java code to illustrate first()import java.util.*;import java.util.TreeSet;  public class TreeSetDemo {    public static void main(String args[])    {        // Creating an empty TreeSet        TreeSet<String> tree = new TreeSet<String>();          // Use add() method to add elements into the Set        tree.add("Welcome");        tree.add("To");        tree.add("Geeks");        tree.add("Ab");        tree.add("TreeSet");        tree.add("B");          // Displaying the TreeSet        System.out.println("TreeSet: " + tree);          // Displaying the lowest element of the set        System.out.println("The first element is: " + tree.first());    }} |
TreeSet: [Ab, B, Geeks, To, TreeSet, Welcome] The first element is: Ab
Program 3: When the elements are of string types but with integer values. Here we see that the digit appearing first is considered as first element irrespective of length:
// Java code to illustrate first()import java.util.*;import java.util.TreeSet;  public class TreeSetDemo {    public static void main(String args[])    {        // Creating an empty TreeSet        TreeSet<String> tree = new TreeSet<String>();          // Use add() method to add elements into the Set        tree.add("Welcome");        tree.add("To");        tree.add("Geeks");        tree.add("45");        tree.add("100");        tree.add("5");          // Displaying the TreeSet        System.out.println("TreeSet: " + tree);          // Displaying the lowest element of the set        System.out.println("The first element is: " + tree.first());    }} |
TreeSet: [100, 45, 5, Geeks, To, Welcome] The first element is: 100
