In this article, we will discuss how to convert Stream into a TreeSet in Java 1.8 version using Stream API. TreeSet doesn’t allow duplicates but maintains sorting order either in natural/reverse order.

Stream to TreeSet :

Using Collectors.toSet()
Using Collectors.toCollection()

1. Using Collectors.toSet()

First, convert Stream to Set using collect() method of Stream API by passing Collectors.toSet() as input argument
Above conversion yields Set and not TreeSet
For Set to TreeSet conversion, create TreeSet object and pass above set as constructor-argument and this will conversion stores elements in alphabetical order
Finally, print converted TreeSet elements to console

StreamToTreeSetUsingCollectorsToSet.java

package net.bench.resources.stream.to.list;

import java.util.TreeSet;
import java.util.Set;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class StreamToTreeSetUsingCollectorsToSet {

	public static void main(String[] args) {

		// 1. Stream of String tokens
		Stream<String> nameStream = Stream.of(
				"Rajiv",
				"Anbu",
				"Santosh",
				"Abdul",
				"Lingaraj"
				);


		// 2. convert Stream<String> to Set<String>
		Set<String> names = nameStream.collect(Collectors.toSet());


		// 3. Set<String> to TreeSet<String>
		TreeSet<String> tSetNames = new TreeSet<String>(names);


		// 4. print to console
		System.out.println("Stream to TreeSet : \n\n" + tSetNames);
	}
}

Output:

Stream to TreeSet : 

[Abdul, Anbu, Lingaraj, Rajiv, Santosh]

2. Using Collectors.toCollection()

Convert Stream to TreeSet using collect() method of Stream API by passing Collectors.toCollection(TreeSet::new) as input argument directly
This direct conversion stores elements in alphabetical order
Print converted TreeSet elements to console

StreamToHashSetUsingCollectorsToCollection.java

package net.bench.resources.stream.to.list;

import java.util.TreeSet;
import java.util.stream.Collectors;
import java.util.stream.Stream;

public class StreamToTreeSetUsingCollectorsToCollection {

	public static void main(String[] args) {

		// 1. Stream of String tokens
		Stream<String> nameStream = Stream.of(
				"Rajiv",
				"Anbu",
				"Santosh",
				"Abdul",
				"Lingaraj"
				);


		// 2. convert Stream<String> to TreeSet<String>
		TreeSet<String> lhSetNames = nameStream
				.collect(Collectors.toCollection(TreeSet::new));


		// 3. print to console
		System.out.println("Stream to TreeSet : \n\n" + lhSetNames);
	}
}

Output:

Stream to TreeSet : 

[Abdul, Anbu, Lingaraj, Rajiv, Santosh]

References:

Happy Coding !!
Happy Learning !!

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Java tutorial for beginners

Java 8 – Convert Stream to TreeSet

Stream to TreeSet :

1. Using Collectors.toSet()

StreamToTreeSetUsingCollectorsToSet.java

2. Using Collectors.toCollection()

StreamToHashSetUsingCollectorsToCollection.java

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References:

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Stream to TreeSet :

1. Using Collectors.toSet()

StreamToTreeSetUsingCollectorsToSet.java

2. Using Collectors.toCollection()

StreamToHashSetUsingCollectorsToCollection.java

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