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TreeMap tailMap() Method in Java

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The java.util.TreeMap.tailMap(from_Key) method in Java is used to get a part or view of the map whose keys are greater than equal to the from_key in the parameter. Any changes made in one map will reflect the change in the other map.

Syntax:

Tree_Map.tailMap(from_Key)

Parameters: The method takes one parameter from_key of the Key type in the TreeMap and refers to the key which is set as the lower point greater than whose mappings are to be returned.

Return Value: The method returns the portion of the mapping whose keys are greater than the from_Key.

Exceptions: The method throws three types of exception:

  • ClassCastException: This exception is thrown if the parameters mentioned in the method cannot be compared with the keys of this map.
  • NullPointerException: This exception is thrown if either of the parameters is of null type and the map does not accept any null values.
  • IllegalArgumentException: This exception is thrown if the mentioned parameters are out of range or the lower end is greater than the higher end.

Below programs illustrate the working of java.util.TreeMap.tailMap() method:
Program 1:




// Java code to illustrate the tailMap() method
import java.util.*;
  
public class Tree_Map_Demo {
    public static void main(String[] args)
    {
  
        // Creating an empty TreeMap
        TreeMap<Integer, String> tree_map = new TreeMap<Integer, String>();
  
        // Mapping string values to int keys
        tree_map.put(10, "Geeks");
        tree_map.put(15, "4");
        tree_map.put(20, "Geeks");
        tree_map.put(25, "Welcomes");
        tree_map.put(30, "You");
  
        // Displaying the TreeMap
        System.out.println("The original map is: "
                           + tree_map);
  
        // Displaying the submap
        System.out.println("The tailMap is " + tree_map.tailMap(15));
    }
}


Output:

The original map is: {10=Geeks, 15=4, 20=Geeks, 25=Welcomes, 30=You}
The tailMap is {15=4, 20=Geeks, 25=Welcomes, 30=You}

Program 2:




// Java code to illustrate the tailMap() method
import java.util.*;
  
public class Tree_Map_Demo {
    public static void main(String[] args)
    {
  
        // Creating an empty TreeMap
        TreeMap<String, Integer> tree_map = new TreeMap<String, Integer>();
  
        // Mapping int values to string keys
        tree_map.put("Geeks", 10);
        tree_map.put("4", 15);
        tree_map.put("Geeks", 20);
        tree_map.put("Welcomes", 25);
        tree_map.put("You", 30);
  
        // Displaying the TreeMap
        System.out.println("The original map is: "
                           + tree_map);
  
        // Displaying the tailMap
        System.out.println("The tailMap is " + tree_map.tailMap("Geeks"));
    }
}


Output:

The original map is: {4=15, Geeks=20, Welcomes=25, You=30}
The tailMap is {Geeks=20, Welcomes=25, You=30}

Program 3: By default, the from_key is included in the tail_Map. If it needs to be ignored or excluded then another parameter can be passed along with the from_key and that is false.




// Java code to illustrate the tailMap() method
import java.util.*;
  
public class Tree_Map_Demo {
    public static void main(String[] args)
    {
  
        // Creating an empty TreeMap
        TreeMap<String, Integer> tree_map = new TreeMap<String, Integer>();
  
        // Mapping int values to string keys
        tree_map.put("Geeks", 10);
        tree_map.put("4", 15);
        tree_map.put("Geeks", 20);
        tree_map.put("Welcomes", 25);
        tree_map.put("You", 30);
  
        // Displaying the TreeMap
        System.out.println("The original map is: "
                           + tree_map);
  
        // Displaying the tailMap
        System.out.println("The tailMap is " + tree_map.tailMap("Geeks", false));
    }
}


Output:

The original map is: {4=15, Geeks=20, Welcomes=25, You=30}
The tailMap is {Welcomes=25, You=30}


Last Updated : 11 Jul, 2018
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