HTML tutorial
CSS3 tutorial
Bootstrap tutorial
JavaScript tutorial
JQuery tutorial
AngularJS tutorial
React tutorial
NodeJS tutorial
PHP tutorial
Python tutorial
Python3 tutorial
Django tutorial
Linux tutorial
Docker tutorial
Ruby tutorial
Java tutorial
C tutorial
C ++ tutorial
Perl tutorial
JSP tutorial
Lua tutorial
Scala tutorial
Go tutorial
ASP.NET tutorial
C # tutorial
A HashSet is a collection of items where every item is unique, and it is found in the java.util package
A HashSet is a collection of items where every item is unique, and it is found in the java.util
package:
Create a HashSet
object called cars that will store strings:
import java.util.HashSet; // Import the HashSet class
HashSet<String> cars = new HashSet<String>();
The HashSet
class has many useful methods. For example, to
add items to it, use the add()
method:
// Import the HashSet class
import java.util.HashSet;
public class Main {
public static void main(String[] args) {
HashSet<String> cars = new HashSet<String>();
cars.add("Volvo");
cars.add("BMW");
cars.add("Ford");
cars.add("BMW");
cars.add("Mazda");
System.out.println(cars);
}
}
To check whether an item exists in a HashSet, use the contains()
method:
To remove an item, use the remove()
method:
To remove all items, use the clear()
method:
To find out how many items there are, use the size
method:
Loop through the items of an HashSet
with a for-each loop:
Items in an HashSet are actually objects. In the examples above, we created
items
(objects) of type "String". Remember that a String in Java is an object (not a primitive type). To use other types, such as int, you must specify an equivalent wrapper class: Integer
. For other primitive types,
use: Boolean
for boolean, Character
for char, Double
for double,
etc:
Use a HashSet
that stores Integer
objects:
import java.util.HashSet;
public class Main {
public static void main(String[] args) {
// Create a HashSet object called numbers
HashSet<Integer> numbers = new HashSet<Integer>();
// Add values to the set
numbers.add(4);
numbers.add(7);
numbers.add(8);
// Show which numbers between 1 and 10 are in the set
for(int i = 1; i <= 10; i++) {
if(numbers.contains(i)) {
System.out.println(i + " was found in the set.");
} else {
System.out.println(i + " was not found in the set.");
}
}
}
}