TreeMap tailMap() Method in Java

Last Updated : 11 Jul, 2018

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

// 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

// 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

// 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}

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TreeMap tailMap() Method in Java

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