Java HashSet remove() method explained

The Java HashSet class implements the remove() method from the Set interface that you can use to remove an element from your HashSet instance.

You need to specify the element to remove as the parameter to the method:

HashSet.remove(Object O);

The parameter you passed to the method assumes the Generic type Object you passed to the HashSet instance during initialization.

The remove() method will return true when an element is found and removed, or false when it fails.

For example, suppose you create a HashSet of <String> type as shown below:

public static void main(String args[])
{
    HashSet<String> mySet = new HashSet<>();
    mySet.add("Tiger");
    mySet.add("Lion");
    mySet.add("Hyena");
}

Then you can remove an element from mySet variable as follows:

public static void main(String args[])
{
    HashSet<String> mySet = new HashSet<>();
    mySet.add("Tiger");
    mySet.add("Lion");
    mySet.add("Hyena");

    mySet.remove("Tiger");
    System.out.println("HashSet content: " + mySet);
}

The output will be as shown below:

HashSet content: [Lion, Hyena]

Additionally, Java won’t throw an error when you pass an Integer as the parameter of the remove() method even though you use the <String> Generic Type during initialization.

Java will return false for any value not found inside the HashSet even when the parameter type is different than your Generic Type:

public static void main(String args[])
{
    HashSet<String> mySet = new HashSet<>();
    mySet.add("Tiger");
    mySet.add("Lion");
    mySet.add("Hyena");

    System.out.println(mySet.remove("Lion")); // true
    System.out.println(mySet.remove("Horse")); // false
    System.out.println(mySet.remove(92)); // false
}

You can use the return value of the remove() method to inform the user whether the specified element is removed or not.