In this tutorial we will see how to initialize HashSet in java . We can create a set in java using different methods . Let’s discuss various method for java set initialization with examples .
Initialize Hashset Java With Examples
We can initialize set java using constructor , set.add() method , Collections methods and Anonymous Subclass. Now We will discuss these methods with examples .
1. Initialize HashSet java – Using Constructor
HashSet have four type constructors in java . We can create a set in java using these constructors .
HashSet<String> hashSet = new HashSet<>();
HashSet<String> hashSet = new HashSet<>(5);
HashSet<String> hashSet = new HashSet<>(5,9);
HashSet<String> hashSet = new HashSet<>(set);
In this example , we initialize HashSet java using constructor . Firstly we initialize array of String then convert array to List and then provide this to HashSet constructor that accepts another collection . Let’s see java program for java set initialization using constructor .
import java.util.Arrays;
import java.util.HashSet;
public class HashSetInitialize {
public static void main(String[] args) {
//initialize array of String
String [] arr = {"JavaVogue","Welcomes","You"};
//Constructs a new set containing the
//elements in the specified collection
HashSet<String> hashSet = new HashSet<>(Arrays.asList(arr));
//print HashSet element
System.out.println("HashSet Elements : "+ hashSet);
}
}
Output:
HashSet Elements : [JavaVogue, You, Welcomes]
2. Java Initialize HashSet Using add() Method
In this example, We will initialize hashset in java using add() method . We create HashSet by empty constructor and then add elements in this set using add() method .
import java.util.HashSet;
public class HashSetInitialize1 {
public static void main(String[] args) {
HashSet<String> hashSet = new HashSet<String>();
//add element in it
hashSet.add("JavaVogue");
hashSet.add("Welcomes");
hashSet.add("You");
//display the element
System.out.println("HashSet Elements : "+ hashSet);
}
}
Output:
HashSet Elements : [JavaVogue, You, Welcomes]
3. Java Immutable Set Initialize
In this example we will initialize java immutable Set . Firstly we create HashSet and add element in it using add() method . Then provide this HashSet to Collections.unmodifiableSet() method to initialize java immutable Set .
import java.util.Collections;
import java.util.HashSet;
import java.util.Set;
public class HashSetInitialize2 {
public static void main(String[] args) {
HashSet<String> hashSet = new HashSet<String>();
// add element in it
hashSet.add("JavaVogue");
hashSet.add("Welcomes");
hashSet.add("You");
// initializing Set using Collections.unmodifiableSet
Set<String> set = Collections.unmodifiableSet(hashSet);
System.out.println("Set Elements : " + set);
}
}
Output:
Set Elements : [JavaVogue, You, Welcomes]
4. Java Empty Set Initialize
We will create empty set in java and initialize it using Collections.addAll() method in this example . We firstly we will initialize HashSet (hashset) and create empty set using Collections.<String> emptySet() method . Now provides hashset to Collections.addAll() to initialize empty set in java .
import java.util.Collections;
import java.util.HashSet;
import java.util.Set;
public class HashSetInitialize3 {
public static void main(String[] args) {
HashSet<String> hashSet = new HashSet<String>();
// add element in it
hashSet.add("JavaVogue");
hashSet.add("Welcomes");
hashSet.add("You");
//create empty Set
Set<String> set = Collections.<String> emptySet();
System.out.println("Set Elements : "+ set);
//initialize Empty Set using Collections.addAll() method
Collections.addAll(set = hashSet);
System.out.println("After initialize empty Set Elements are : "+ set);
}
}
Output:
Set Elements : []
After initialize empty Set Elements are : [JavaVogue, You, Welcomes]
5. Collections.singleton()
Now , If you want to create a set containing only a single element, then we can use Collections.singleton() that returns an immutable set containing that only one element. If any modification operation is performed on it , then set will throw an UnsupportedOperationException .
import java.util.Collections;
import java.util.Set;
public class HashSetInitialize4 {
public static void main(String[] args) {
Set<Integer> set = Collections.singleton(1);
System.out.println("Singleton Set : "+ set);
}
}
Output:
Singleton Set : [1]
6. Initialize HashSet Java Using Anonymous Subclass
We can initialize HashSet java with the help of anonymous subclass . But we should avoid this way to java set initialization because first we create anonymous class here then set , it might me create problem of memory leak.
import java.util.HashSet;
public class HashSetInitialize5 {
public static void main(String[] args) {
HashSet<String> hashSet = new HashSet<String>() {{
add("JavaVogue");
add("Welcomes");
add("You");
}};
System.out.println("HashSet Elements : "+ hashSet);
}
}
Output:
HashSet Elements : [JavaVogue, You, Welcomes]
In this tutorial we learned about initialize HashSet java using various method with examples .Now you can do java set initialization easily . You can learn more Java HashSet program for practice.
Reference :