How to Find All Duplicates in a List in Java

Need to find all the duplicates in a Java List? Maybe a Java ArrayList, a Vector or even just an array? There are a few different approaches you can take

- I prefer the use of the Java Streams API to find all duplicates in a List.
- The use of a HashSet to find all the duplicates was popular before the Streams API was released.
- A brute force comparison to dedupe a list using nested loops is a popular approach to help learn language syntax.
- A combined use of multiple Lists and HashSets is fun too!

In this video tutorial on how to find Java List duplicates, we demonstrate each of these approaches, including a way to use the Java Collections class to find the frequency of duplicates in a List as well.

If you want to find all the duplicates in a list, and eventually remove those duplicates, this quick Java tutorial on deduping is for you!

[scrumtuous]

I like the Streams approach to finding and removing duplicates from the Java list.

[cameronmcnz]

I said that I wrote the Java list duplicate finder and removal articles. I didn’t. Walker Aldridge did.