Find Duplicate Elements from list using Java 8 | Java 8 coding Interview Questions | Code Decode

Published: 09 March 2022
on channel: Code Decode

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In this video of code decode we have covered Java 8 coding Interview Questions and Answers where we have covered Find duplicates from a list using java 8

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How to find duplicate elements in a Stream in Java 8

Using Set.add() method:
If the element is present in the Set already, then this Set.add() returns false. we can collect them.
Set.add() returns false if the element was already present in the set. filter such element and Collect duplicate elements in the set

How to find duplicate elements in a Stream in Java
Using Collectors.groupingBy():

The groupingBy() method of Collectors class in Java groups the objects by some property. So we will pass the property of redundancy and collect the result in a Set.

For each element in the stream, group them along with their frequency in a map, using Collectors.groupingBy() method.Then for each element in the collected map, if the frequency of any element is more than one, then this element is a duplicate element.

stream() .collect(Collectors.groupingBy( Function.identity(), Collectors.counting()))
// Convert this map into a stream
.entrySet().stream()
// Check if frequency 1// for duplicate elements // Find such elements
.filter(m - m.getValue() 1).map(Map.Entry::getKey)
// And Collect them in a Set
.collect(Collectors.toSet());

How to find duplicate elements in a Stream in Java

Collections.frequency(list, i)

count the frequency of each element, using Collections.frequency() method. Then for each element in the collection list, if the frequency of any element is more than one, then this element is a duplicate element.

stream().filter(i - Collections.frequency(list, i) 1)
.collect(Collectors.toSet());

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