Java Set.remove() Method

In Java, a Set is an interface defined in java.util package. Set is a collection that cannot contain duplicate elements.

In many applications of sets, one may find the necessity to delete elements conditionally or without condition. In order to perform the remove operation on a set the Set interface provides the remove() method. It allows programmer to operate and manipulate sets dynamically.

Set.remove() Method

The remove() method removes the specified element from the set if it is present. It removes an element e such that (o==null ? e==null : o.equals(e)), if the set contains such an element. The method returns true if the set contains the element, else returns false.

Syntax:

Where, o is an object to be removed from this set, if present.

The method throws the following three exceptions:

Output:

Original Set: [Apple, Banana, Orange]
Removed Banana? true
Updated Set: [Apple, Orange]

Removing Elements While Iterating (Using Iterator)

Using Set.remove() directly while iterating over a set using a for-each loop can cause a ConcurrentModificationException. The correct way is to use an iterator.

Output:

Filtered Set: [20, 25] 

Removing Elements Conditionally Using Collection.removeIf() Method

Since Java 8, there has been a method called removeIf(), which can be used to remove elements that meet a certain condition based on lambda expressions.

Output:

Set after conditional removal: [10, 15] 

This approach improves code readability and is preferred for filtering based on conditions.

Common Mistakes with Set.remove() Method

1. Modifying while iterating: Use an iterator or removeIf() instead of changing the set during a for-each loop.
2. NullPointerException: Ensure the set does not contain nulls when calling remove(null) in TreeSet.
3. Assuming Order: HashSet does not maintain insertion order, so removal based on position is not valid.

Best Practices

1. Always check the return value of remove() if needed to verify successful removal.
2. Prefer removeIf() for conditional removal over manual iteration.
3. Use appropriate Set implementation based on ordering and performance needs.
4. Avoid modifying the set during a for-each loop-use iterators instead.

Important Points to Remember

1. The Set.remove() method removes a single specified object.
2. Removing from a HashSet is generally fast (O(1)).
3. Use Collection.removeIf() for batch deletions based on conditions.
4. Use iterators for safe removal during traversal.

Conclusion

The Set.remove() method is a simple but effective instrument of working with the elements of a collection. Whenever you are deleting one element, filtering data conditionally or cleaning up an entire set, it is important to understand how and when to use the remove() method effectively.

Java Set MCQs

1. In which of the following package the remove() method is defined?

1. java.util.stream
2. java.util.zip
3. java.util.concurrent
4. java.util

2. Which of the following exception does not throw the Set.remove() method?

1. ClassCastException
2. NullPointerException
3. IOException
4. UnsupportedOperationException

3. Which of the following method you will use if the conditional remove operation to perform?

1. Collection.removeIf()
2. Set.remove()
3. Iterator.remove()
4. None of the above

4. The remove() method returns a __________ value?

1. Integer
2. Boolean
3. Object
4. None of the above

5. The remove() method removes the ___________ element from the set?

1. First
2. Second
3. Middle
4. Specified