Java HashSet remove() method example

java.util.HashSet remove(Object o)

Description

On this document we will be showing a java example on how to use the remove() method of HashSet Class. Basically this method provide a facility to remove an element of the HashSet object. A boolean returned value will indicate if the removal of element succeeded.It will return true if it is, otherwise false. If the HashSet does not contain the same as what we are trying to add, a return value would be false. Make a note that a HashSet is unsorted thus the order of elements are random, better watch out on this concept.

The HashSet as majority of the Collection classes make use of Generics such that if we have declared our set like HashSet set = new HashSet() then the elements of inside our set is of type String. And we cannot insert different object type not unless its a subclass of the object declaration, otherwise a runtime error will be thrown.

The HashSet elements are unique, there would be no two identical elements that can exist.

Important notes for remove() method:

specified by remove in interface Collection<E>
specified by remove in interface Set<E>
overrides remove in class AbstractCollection<E>

Method Syntax

public boolean remove(Object o)

Method Argument

Data Type	Parameter	Description
Object	o	element to be removed to this set if it is present

Method Returns

The remove(Object o) method returns true if the set contained the specified element.

Compatibility

Requires Java 1.2 and up

Java HashSet remove() Example

Below is a java code demonstrates the use of remove() method of HashSet class. The example presented might be simple however it shows the behavior of the remove() method.

package com.javatutorialhq.java.examples;

import static java.lang.System.*;

import java.util.HashSet;

/*
 * This example source code demonstrates the use of  
 * remove() method of HashSet class
 */

public class HashSetRemoveExample {

	public static void main(String[] args) throws InterruptedException {

		// get the HashMap object from the method init()
		HashSet studentSet = init();

		// remove an element
		boolean result = studentSet.remove("Sharon Wallace");
		if (result) {
			out.println("Element successfully removed");
		} else {
			out.println("Element were not present");
		}

		// remove an element that is not present
		result = studentSet.remove("Darwin Ingram");
		if (result) {
			out.println("Element successfully removed");
		} else {
			out.println("Element were not present");
		}

	}

	private static HashSet init() {
		// declare the HashSet object
		HashSet studentSet = new HashSet<>();
		// put contents to our HashMap
		studentSet.add("Shyra Travis");
		studentSet.add("Sharon Wallace");
		studentSet.add("Leo Batista");

		return studentSet;
	}

}

There are two methods created on the above example, main() and init. The main method calls the init() which initializes and assign values to a HashSet object. The main() method assign to a new HashSet object the returned object by the init() method. An element were tried to be removed to the set by calling the remove() method. Based on the returned value, we have evaluated if the removal is successful or not. If the result is false, the element we are trying to remove is not present.

Sample Output

Below is the sample output when you run the above example.

References

Oracle Java Documentation