Besides the AbstractMap Class, Java's TreeMap is utilized to implement the NavigableMap and Map interface. Depending on the function Object() used, the map is ordered either by the Comparator available at map formation or by the logical ordering of its keys. In this article, we will discuss Java treemap, its features, and various key points to remember while working with treemap. We will also discuss the construction process of a treemap along with constructors, methods, and multiple examples related to treemap.
The Java TreeMap class implements red-black trees. It offers a practical way to keep the key-values organized. It can also be defined as an implementation of NavigableMap based on Red-Black trees. It is arranged in the order that its keys naturally appear.
Similar to the HashMap class, the TreeMap class implements the Map interface. The primary distinction between both is that TreeMap is sorted in ascending order of its keys whereas HashMap is an unsorted collection.
The key-value pairs can be sorted and stored effectively using this method. Similar to any other sorting map, the treemap's storage order has to be constant with equals regardless of the specified comparators. The implementation of a treemap isn’t accompanied in the sense that a map must be externally synchronized if it is used by many threads simultaneously and one of the threads changes the map fundamentally.
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The following are the Java TreeMap class key points to remember:
Based on the key, Java TreeMap contains values. It extends the AbstractMap class and implements the NavigableMap interface.
Java TreeMap only has distinct elements.
We must first import the java.util.TreeMap package in order to create a TreeMap. Here is how to make a Java TreeMap after importing the library.
TreeMap <Key, Value> num = new TreeMap();
Here,
key: is a special identification number used to link each value (element) in a map.
Value: elements on a map that are linked by keys
Without using any arguments, we generated a TreeMap using the name numbers in the code above. In this instance, TreeMap's elements are organically sorted (ascending order).
However, by utilizing the Comparator interface, we may adjust how the components are sorted. It will be covered in more detail later in this course.
We must first build a TreeMap class’s object in order to generate a TreeMap. The class of TreeMap has a number of constructors that can be used to create a TreeMap. The constructors accessible in the class are listed below. Following are constructors in a treemap:
By leveraging the keys' natural order, this function Object() creates an empty treemap to be sorted.
Let us see the Java example below to understand the working of this treemap() constructor.
import java.util.*;
import java.util.concurrent.*;
public class HKR {
static void XConstructor()
{
TreeMap<Integer, String> tree_map
= new TreeMap<Integer, String>();
tree_map.put(10, "Hello!");
tree_map.put(15, "How");
tree_map.put(20, "Are");
tree_map.put(25, "You");
tree_map.put(30, "Dear");
System.out.println("The TreeMap is: " + tree_map);
}
public static void main(String[] args)
{
System.out.println("TreeMap by using the "
+ "TreeMap() constructor is:\n");
XConstructor();
}
}
The Output of this Java code will be:
TreeMap by using the TreeMap() constructor is:
The TreeMap is: {10=Hello!, 15=How, 20=Are, 25=You, 30=Dear}
This function Object() is used for creating a TreeMap object which is empty and whose members require external sorting order specification.
Let us see the Java example below to understand the working of this Treemap(comparator comp) constructor.
import java.util.*;
import java.util.concurrent.*;
class Stud1 {
int rollno;
String name, address;
public Stud1(int rollno, String name, String address)
{
this.rollno = rollno;
this.name = name;
this.address = address;
}
public String toString()
{
return this.rollno + " " + this.name + " "
+ this.address;
}
}
class Sortbyroll implements Comparator{
public int compare(Stud1 a, Stud1 b)
{
return a.rollno - b.rollno;
}
}
public class HKR {
static void Example2ndConstructor()
{
TreeMap<Stud1, Integer> tree_map
= new TreeMap<Stud1, Integer>(
new Sortbyroll());
tree_map.put(new Stud1(111, "x", "Arabic"), 2);
tree_map.put(new Stud1(131, "y", "Banana"), 3);
tree_map.put(new Stud1(121, "z", "Costa"), 1);
System.out.println("TreeMap: " + tree_map);
}
public static void main(String[] args)
{
System.out.println("TreeMap using "
+ "TreeMap(Comparator)"
+ " constructor will be:\n");
Example2ndConstructor();
}
}
The Output of this Java code will be:
TreeMap using TreeMap(Comparator) constructor will be:
TreeMap: {111 y Banana=2, 121 z Costa=1, 131 x Arabic=3}
When calling this function, the elements from the supplied map X will be ordered according to the key's natural order to initialize a TreeMap.
Let us see the Java example below to understand the working of this constructor.
import java.util.*;
import java.util.concurrent.*;
public class TreeMapImplementation {
static void ExampleConstructor()
{
Map<Integer, String> hash_map
= new HashMap<Integer, String>();
hash_map.put(10, "Hello!");
hash_map.put(15, "How");
hash_map.put(20, "are");
hash_map.put(25, "you");
hash_map.put(30, "Dear");
TreeMap<Integer, String> tree_map
= new TreeMap<Integer, String>(hash_map);
System.out.println("TreeMap: " + tree_map);
}
public static void main(String[] args)
{
System.out.println("TreeMap using "
+ "TreeMap(Map)"
+ " constructor is:\n");
ExampleConstructor();
}
}
The Output of this Java code will be:
TreeMap using TreeMap(Map) constructor is:
TreeMap: {10=Hello!, 15=How, 20=are, 25=you, 30=Dear
The items from the specified sorted map will also be stored in a similar arrangement as the specified sorted map when using this function Object() to initialize a TreeMap.
Let us see the Java example below to understand the working of this constructor.
import java.util.*;
import java.util.concurrent.*;
public class HKR {
static void ExampleConstructor()
{
SortedMap<Integer, String> sorted_map
= new ConcurrentSkipListMap<Integer, String>();
sorted_map.put(10, "Hello!");
sorted_map.put(15, "How");
sorted_map.put(20, "are");
sorted_map.put(25, "you");
sorted_map.put(30, "Dear");
TreeMap<Integer, String> tree_map
= new TreeMap<Integer, String>(sorted_map);
System.out.println("TreeMap: " + tree_map);
}
public static void main(String[] args)
{
System.out.println("TreeMap using "
+ "TreeMap(SortedMap)"
+ " constructor:\n");
ExampleConstructor();
}
}
The Output of this Java code will be:
TreeMap using TreeMap(SortedMap) constructor:
TreeMap: {10=Hello!, 15=How, 20=are, 25=you, 30=Dear}
Here are a lot of methods for Java Treemap. Let us have a look at them below:
Let us now see a Treemap example below:
import java.util.*;
class TreeMap1{
public static void main(String args[]){
TreeMap<Integer,String> map=new TreeMap<Integer,String>();
map.put(1,"Apple");
map.put(2,"Banana");
map.put(3,"Cherry");
map.put(4,"Dolce");
for(Map.Entry m:map.entrySet()){
System.out.println(m.getKey()+" "+m.getValue());
}
}
}
The output of this program will be:
1 Apple 2 Banana 3 Cherry 4 Dolce
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We can employ the put() method to include a new element in the TreeMap. The TreeMap, however, does not maintain the order of insertion. The keys will be evaluated and sorted. It will be done in increasing order internally for each element.
Let us understand this better with the help of an example:
import java.util.*;
class HKR {
public static void main(String args[])
{
TreeMap tm1 = new TreeMap();
tm1.put(3, "HKR");
tm1.put(2, "Trainings");
tm1.put(1, "for learners");
TreeMap<Integer, String> tm2
= new TreeMap<Integer, String>();
tm2.put(new Integer(3), "HKR");
tm2.put(new Integer(2), "Trainings");
tm2.put(new Integer(1), "for learners");
System.out.println(tm1);
System.out.println(tm2);
}
}
The output of this program will be:
{1=for learners, 2=Trainings, 3=HKR}
{1=for learners, 2=Trainings, 3=HKR}
In case we want to update an element after adding it, we can do so by adding it once more using the put() method. The values of the keys can be modified by simply inputting the updated value of the key that needs to be changed because the items in the treemap are indexed that use the keys.
Let us understand this better with the help of an example:
import java.util.*;
class HKR {
public static void main(String args[])
{
TreeMap<Integer, String> tm
= new TreeMap<Integer, String>();
tm.put(3, "Welcome");
tm.put(2, "to");
tm.put(1, "HKR");
System.out.println(tm);
tm.put(2, "to");
System.out.println(tm);
}
}
The output of this program will be:
{1=HKR, 2=to, 3=Welcome}
{1=HKR, 2=to, 3=Welcome}
The remove() method can be used to delete an item from the TreeMap. If there is a mapping for the key in the treemap, it is removed by this method using the key value.
Let us understand this better with the help of an example:
import java.util.*;
class HKR {
public static void main(String args[])
{
TreeMap<Integer, String> tm
= new TreeMap<Integer, String>();
tm.put(3, "Welcome");
tm.put(2, "to");
tm.put(1, "HKR");
tm.put(4, "Learners");
System.out.println(tm);
tm.remove(4);
System.out.println(tm);
}
}
The output of this program will be:
{1=HKR, 2=to, 3=Welcome, 4=Learners}
{1=HKR, 2=to, 3=Welcome}
The Map can be iterated through in a variety of ways. The most well-known method is to obtain the keys using a for-each loop. The getValue() method is used to determine the key's value.
Let us understand this better with the help of an example:
import java.util.*;
class HKR {
public static void main(String args[])
{
TreeMap<Integer, String> tm
= new TreeMap<Integer, String>();
tm.put(3, "Welcome");
tm.put(2, "to");
tm.put(1, "HKR");
for (Map.Entry mapElement : tm.entrySet()) {
int key = (int)mapElement.getKey();
String value = (String)mapElement.getValue();
System.out.println(key + " : " + value);
}
}
}
The output of this program will be:
1 : HKR
2 : to
3: Welcome
Below are a few features of Java Treemap:
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Conclusion
In this article, we have learned about treemaps in Java. The Java TreeMap class implements red-black trees. It offers a practical way to keep key-value pairs organized. It can also be defined as an implementation of NavigableMap based on Red-Black trees. It is arranged in the order that its keys naturally appear. We have also talked about various features of Java treemap along with the methods related to it. We have also discussed the constructors of the treemap.
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