The pollFirstEntry() method of NavigableMap interface in Java is used to remove and return a key-value mapping associated with the least key in this map, or null if the map is empty.
Syntax:
Map.Entry< K, V > pollFirstEntry()
Where, K is the type of key maintained by this map and V is the type of values mapped to the keys.
Parameters: This function does not accepts any parameter.
Return Value: It returns a key-value mapping associated with the least key after removing it from this map, or null if the map is empty.
Below programs illustrate the pollFirstEntry() method in Java:
Program 1: When the key is integer.
// Java code to demonstrate the working of// pollFirstEntry() method  import java.io.*;import java.util.*;  public class GFG {      public static void main(String[] args)    {          // Declaring the NavigableMap of Integer and String        NavigableMap<Integer, String> nmmp = new TreeMap<>();          // assigning the values in the NavigableMap        // using put()        nmmp.put(2, "two");        nmmp.put(7, "seven");        nmmp.put(3, "three");          System.out.println("First removed key-value from the map : "                           + nmmp.pollFirstEntry());    }} |
Output:
First removed key-value from the map : 2=two
Program 2: When the key is string.
// Java code to demonstrate the working of// pollFirstEntry() method  import java.io.*;import java.util.*;  public class GFG {      public static void main(String[] args)    {          // Declaring the NavigableMap of Integer and String        NavigableMap<String, String> tmmp = new TreeMap<>();          // assigning the values in the NavigableMap        // using put()        tmmp.put("one", "two");        tmmp.put("six", "seven");        tmmp.put("two", "three");          System.out.println("First removed key-value from the map : "                                          + tmmp.pollFirstEntry());    }} |
Output:
First removed key-value from the map : one=two
Reference: https://docs.oracle.com/javase/10/docs/api/java/util/NavigableMap.html#pollFirstEntry()
