Java HashSet

Java Collections Framework

HashSet is implemented based on HashMap and is a collection that does not allow duplicate elements.

HashSet allows null values.

HashSet is unordered, meaning it does not maintain the insertion order.

HashSet is not thread-safe. If multiple threads attempt to modify a HashSet concurrently, the final result is unpredictable. You must explicitly synchronize concurrent access to a HashSet when accessed by multiple threads.

HashSet implements the Set interface.

sites.remove("Taobao");  // Removes the element, returns true if successful, otherwise false
System.out.println(sites);
}
}

Executing the above code will output the following result:

[Google, tutorialpro, Zhihu]

To remove all elements from the collection, you can use the clear method:

Example

// Import HashSet class      
import java.util.HashSet;

public class tutorialproTest {
    public static void main(String[] args) {
    HashSet<String> sites = new HashSet<String>();
        sites.add("Google");
        sites.add("tutorialpro");
        sites.add("Taobao");
        sites.add("Zhihu");
        sites.add("tutorialpro");     // Duplicate elements will not be added
        sites.clear();  
        System.out.println(sites);
    }
}

Executing the above code will output the following result:

[]

Calculating Size

To calculate the number of elements in a HashSet, you can use the size() method:

Example

// Import HashSet class      
import java.util.HashSet;

public class tutorialproTest {
    public static void main(String[] args) {
    HashSet<String> sites = new HashSet<String>();
        sites.add("Google");
        sites.add("tutorialpro");
        sites.add("Taobao");
        sites.add("Zhihu");
        sites.add("tutorialpro");     // Duplicate elements will not be added
        System.out.println(sites.size());  
    }
}

Executing the above code will output the following result:

Iterating Over HashSet

You can use a for-each loop to iterate over the elements in a HashSet.

Example

// Import HashSet class      
import java.util.HashSet;

public class tutorialproTest {
    public static void main(String[] args) {
    HashSet<String> sites = new HashSet<String>();
        sites.add("Google");
        sites.add("tutorialpro");
        sites.add("Taobao");
        sites.add("Zhihu");
        sites.add("tutorialpro");     // Duplicate elements will not be added
        for (String i : sites) {
            System.out.println(i);
        }
    }
}

Executing the above code will output the following result:

Google
tutorialpro
Zhihu
Taobao

For more API methods, you can refer to: https://www.tutorialpro.org/manual/jdk11api/java.base/java/util/HashSet.html

Java Collections Framework ```

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