What does the distinct() method do in the Stream API?

The distinct() method in the Stream API is used to remove duplicate elements from a stream, ensuring that each element appears only once in the final stream. This method is particularly useful when working with collections that may contain duplicates and where you want to process only unique elements. The distinct() method relies on the equals() method of the elements to determine whether two elements are the same, making it important to ensure that the equals() method is correctly implemented for the elements in the stream.

When you apply the distinct() method to a stream, it returns a new stream with the duplicate elements removed. Since distinct() is an intermediate operation, it does not trigger the execution of the stream pipeline by itself. Instead, it creates a new stream that can be further processed by other stream operations, such as filter(), map(), or sorted(). The final result is only produced when a terminal operation, such as collect() or forEach(), is invoked.

The distinct() method is particularly useful in scenarios where you want to eliminate redundancy in your data processing pipeline. For example, if you have a list of transactions and want to ensure that each transaction is processed only once, you can use the distinct() method to remove any duplicate transactions. This method helps improve the accuracy and efficiency of data processing by ensuring that only unique elements are considered.