In Java programming, a set is a collection of distinct elements, i.e., it cannot contain duplicate values. Java provides three built-in classes for working with sets: HashSet, LinkedHashSet, and TreeSet. In this blog post, we will explore these classes in detail, including their similarities and differences, and provide examples of how to use them in Java programs.
HashSet:
HashSet is a class in Java that implements a hash table for storing a collection of unique elements. The elements in a HashSet are not ordered and can be accessed in any order. Here’s an example of how to create a HashSet of strings and add elements to it:
import java.util.HashSet;
public class HashSetExample {
public static void main(String[] args) {
HashSet<String> myHashSet = new HashSet<String>();
myHashSet.add("apple");
myHashSet.add("banana");
myHashSet.add("cherry");
System.out.println(myHashSet);
}
}
In this example, we import the HashSet class, create a HashSet of strings called myHashSet, and add three elements to it. Finally, we print the contents of the HashSet using the System.out.println() method.
LinkedHashSet:
LinkedHashSet is another class in Java that implements a hash table for storing a collection of unique elements, but it maintains the insertion order of the elements. Here’s an example of how to create a LinkedHashSet of integers and add elements to it:
import java.util.LinkedHashSet;
public class LinkedHashSetExample {
public static void main(String[] args) {
LinkedHashSet<Integer> myLinkedHashSet = new LinkedHashSet<Integer>();
myLinkedHashSet.add(1);
myLinkedHashSet.add(2);
myLinkedHashSet.add(3);
System.out.println(myLinkedHashSet);
}
}
In this example, we import the LinkedHashSet class, create a LinkedHashSet of integers called myLinkedHashSet, and add three elements to it. Finally, we print the contents of the LinkedHashSet using the System.out.println() method.
TreeSet:
TreeSet is a class in Java that implements a sorted set using a binary search tree. The elements in a TreeSet are stored in ascending order, and can be accessed in that order. Here’s an example of how to create a TreeSet of doubles and add elements to it:
import java.util.TreeSet;
public class TreeSetExample {
public static void main(String[] args) {
TreeSet<Double> myTreeSet = new TreeSet<Double>();
myTreeSet.add(3.3);
myTreeSet.add(1.1);
myTreeSet.add(2.2);
System.out.println(myTreeSet);
}
}
In this example, we import the TreeSet class, create a TreeSet of doubles called myTreeSet, and add three elements to it. Finally, we print the contents of the TreeSet using the System.out.println() method.
Maps are data structures that allow you to store and manipulate collections of key-value pairs. Java provides several built-in classes for working with maps, including HashMap, LinkedHashMap, and TreeMap. In this blog post, we will explore these classes in detail, including their similarities and differences, and provide examples of how to use them in Java programs.
HashMap:
HashMap is a class in Java that provides an implementation of a hash table. It allows you to add, remove, and access key-value pairs in the table. Here’s an example of how to create a HashMap of strings and integers, add elements to it, and access them:
import java.util.HashMap;
public class HashMapExample {
public static void main(String[] args) {
HashMap<String, Integer> myHashMap = new HashMap<String, Integer>();
myHashMap.put("apple", 1);
myHashMap.put("banana", 2);
myHashMap.put("cherry", 3);
System.out.println(myHashMap.get("apple"));
}
}
In this example, we import the HashMap class, create a HashMap of strings and integers called myHashMap, and add three key-value pairs to it. Finally, we use the get() method to access the value associated with the key “apple” and print it to the console.
LinkedHashMap:
LinkedHashMap is another class in Java that provides an implementation of a hash table, but with one important difference: it maintains the order in which the key-value pairs were added to the table. This makes it more efficient than HashMap for iterating over the elements in the order in which they were added. Here’s an example of how to create a LinkedHashMap of strings and integers, add elements to it, and iterate over them in the order they were added:
import java.util.LinkedHashMap;
import java.util.Map;
public class LinkedHashMapExample {
public static void main(String[] args) {
LinkedHashMap<String, Integer> myLinkedHashMap = new LinkedHashMap<String, Integer>();
myLinkedHashMap.put("apple", 1);
myLinkedHashMap.put("banana", 2);
myLinkedHashMap.put("cherry", 3);
for (Map.Entry<String, Integer> entry : myLinkedHashMap.entrySet()) {
System.out.println(entry.getKey() + ": " + entry.getValue());
}
}
}
In this example, we import the LinkedHashMap and Map classes, create a LinkedHashMap of strings and integers called myLinkedHashMap, and add three key-value pairs to it. Finally, we use a for loop to iterate over the elements in the order they were added and print them to the console.
TreeMap:
TreeMap is a class in Java that provides an implementation of a red-black tree. It allows you to add, remove, and access key-value pairs in the tree, and maintains the order of the keys based on their natural order or a custom comparator. Here’s an example of how to create a TreeMap of strings and integers, add elements to it, and iterate over them in natural order:
import java.util.TreeMap;
import java.util.Map;
public class TreeMapExample {
public static void main(String[] args) {
TreeMap<String, Integer> myTreeMap = new TreeMap<String, Integer>();
myTreeMap.put("apple", 1);
myTreeMap.put("banana", 2);
myTreeMap.put("cherry", 3);
for (Map.Entry<String, Integer> entry : myTreeMap.entrySet()) {
System.out.println(entry.getKey() + ": " + entry.getValue());
}
}In this example, we import the `TreeMap` and `Map` classes, create a `TreeMap` of strings and integers called `myTreeMap`, and add three key-value pairs to it. Finally, we use a for loop to iterate over the elements in the natural order of the keys and print them to the console.