Java TreeMap tailMap() Method

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Description

The Java TreeMap tailMap(K fromKey) method is used to return a view of the portion of this map whose keys are greater than or equal to fromKey. The returned map is backed by this map, so changes in the returned map are reflected in this map, and vice-versa.

Declaration

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

public SortedMap<K,V> tailMap(K fromKey)

Parameters

fromKey − This is the low endpoint (inclusive) of the keys in the returned map.

Return Value

The method call returns a view of the portion of this map whose keys are greater than or equal to fromKey.

Exception

• ClassCastException − This exception is thrown if fromKey is not compatible with this map's comparator.

• NullPointerException − This exception is thrown if fromKey is null and this map uses natural ordering, or its comparator does not permit null keys.

• IllegalArgumentException − This exception is thrown if this map itself has a restricted range, and fromKey lies outside the bounds of the range.

Java TreeMap tailMap(K fromKey,boolean inclusive) Method

Description

The tailMap(K fromKey,boolean inclusive) method is used to return a view of the portion of this map whose keys are greater than (or equal to, if inclusive is true) fromKey. The returned map is backed by this map, so changes in the returned map are reflected in this map, and vice-versa.

Declaration

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

public NavigableMap<K,V> tailMap(K fromKey,boolean inclusive)

Parameters

• fromKey − This is the low endpoint of the keys in the returned map.

• inclusive − This is true if the low endpoint is to be included in the returned view.

Return Value

The method call returns a view of the portion of this map whose keys are greater than (or equal to, if inclusive is true) fromKey.

Exception

• ClassCastException − This exception is thrown if fromKey is not compatible with this map's comparator.

• NullPointerException − This exception is thrown if fromKey is null and this map uses natural ordering, or its comparator does not permit null keys.

• IllegalArgumentException − This exception is thrown if this map itself has a restricted range, and fromKey lies outside the bounds of the range.

Getting TailMap of a TreeMap of Integer,Integer Pair Example

The following example shows the usage of Java TreeMap tailMap(K fromKey) method get a view of the portion of this map whose keys are greater than or equal to fromKey. We've created two TreeMap objects of Integer,Integer pairs. Then few entries are added to first map, and using subMap() we're retrieving and printing the submap from the first map.

package com.tutorialspoint;

import java.util.SortedMap;
import java.util.TreeMap;

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

      // creating maps 
      TreeMap<Integer, Integer> treemap = new TreeMap<>();
      SortedMap<Integer, Integer> treemapincl = new TreeMap<>();

      // populating tree map
      treemap.put(2, 2);
      treemap.put(1, 1);
      treemap.put(3, 3);
      treemap.put(6, 6);
      treemap.put(5, 5);      

      System.out.println("Getting tail map");
      treemapincl = treemap.tailMap(3);
      System.out.println("Tail map values: "+treemapincl);      
   }    
}

Output

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

Getting tail map
Tail map values: {3=3, 5=5, 6=6}

Getting TailMap of a TreeMap of Integer,String Pair Example

The following example shows the usage of Java TreeMap tailMap(K fromKey) method get a view of the portion of this map whose keys are greater than or equal to fromKey. We've created two TreeMap objects of Integer,String pairs. Then few entries are added to first map, and using subMap() we're retrieving and printing the submap from the first map.

package com.tutorialspoint;

import java.util.SortedMap;
import java.util.TreeMap;

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

      // creating maps 
      TreeMap<Integer, String> treemap = new TreeMap<>();
      SortedMap<Integer, String> treemapincl = new TreeMap<>();

      // 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("Getting tail map");
      treemapincl = treemap.tailMap(3);
      System.out.println("Tail map values: "+treemapincl);      
   }    
}

Output

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

Getting tail map
Tail map values: {3=three, 5=five, 6=six}

Getting TailMap of a TreeMap of Integer,String Pair Example

The following example shows the usage of Java TreeMap tailMap(K fromKey, boolean inclusive) method get a view of the portion of this map whose keys are greater than (or equal to, if inclusive is true) fromKey. We've created two TreeMap objects of Integer,String. Then few entries are added to first map, and using tailMap() we're retrieving and printing the tailMap from the first map.

package com.tutorialspoint;

import java.util.NavigableMap;
import java.util.TreeMap;

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

      // creating maps 
      TreeMap<Integer, String> treemap = new TreeMap<>();
      NavigableMap<Integer, String> treemapincl = new TreeMap<>();

      // 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("Getting tail map");
      treemapincl = treemap.tailMap(2, true);
      System.out.println("Tail map values: "+treemapincl);      
   }    
}

Output

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

Getting tail map
Tail map values: {2=two, 3=three, 5=five, 6=six}