java.util.TreeMap.firstKey() Method

Description

The firstKey() method is used to return the first (lowest) key currently in this map.

Declaration

Following is the declaration for java.util.TreeMap.firstKey() method.

public K firstKey()

Parameters

NA

Return Value

The method call returns the first (lowest) key currently in this map.

Exception

NoSuchElementException − This exception is thrown if this map is empty.

Example

The following example shows the usage of java.util.TreeMap.firstKey() method.

package com.tutorialspoint;

import java.util.*;

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

      // creating tree map 
      TreeMap<Integer, String> treemap = new TreeMap<Integer, String>();

      // populating tree map
      treemap.put(2, "two");
      treemap.put(1, "one");
      treemap.put(3, "three");
      treemap.put(6, "six");
      treemap.put(5, "five");

      System.out.println("Checking first key");
      System.out.println("First key is: "+ treemap.firstKey());
   }    
}

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

Checking first key
First key is: 1

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