Java TreeMap pollFirstEntry() Method Example

The pollFirstEntry() method of java.util.TreeMap class removes and returns a key-value mapping associated with the least key in this map, or null if the map is empty.

Signature

public Map.Entry<K,V> pollFirstEntry()

This method removes and returns a key-value mapping associated with the least key in this map, or null if the map is empty.

Example

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

import java.util.Map;
import java.util.TreeMap;

public class PollFirstEntryMethodTreeMapExample 
{
    public static void main(String args[])
    {
        // create an empty TreeMap
        TreeMap<Integer,String>  treeMap1 = new TreeMap<Integer,String>();
        
        // use put() method to put elements to the TreeMap
        treeMap1.put(1,"Element1");
        treeMap1.put(2,"Element2");
        treeMap1.put(3,"Element3");
        treeMap1.put(4,"Element4");
        treeMap1.put(5,"Element5");
        
        //Print the elements of TreeMap before Polling first entry
        System.out.println("**Elements of TreeMap before Polling**");
        for(Map.Entry<Integer,String> entry : treeMap1.entrySet())
        {
            System.out.println("Key : "+entry.getKey()+" ...."+"Value : "+entry.getValue());
        }
        
        //Poll the first entry
        treeMap1.pollFirstEntry();
        
        //Print the elements of TreeMap after Polling first entry
        System.out.println("**Elements of TreeMap after Polling**");
        for(Map.Entry<Integer,String> entry : treeMap1.entrySet())
        {
            System.out.println("Key : "+entry.getKey()+" ...."+"Value : "+entry.getValue());
        }
    }
}

Output

**Elements of TreeMap before Polling**
Key : 1 ....Value : Element1
Key : 2 ....Value : Element2
Key : 3 ....Value : Element3
Key : 4 ....Value : Element4
Key : 5 ....Value : Element5
**Elements of TreeMap after Polling**
Key : 2 ....Value : Element2
Key : 3 ....Value : Element3
Key : 4 ....Value : Element4
Key : 5 ....Value : Element5

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