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Program to convert a Set to Stream in Java using Generics

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Java Set is a part of java.util package and extends java.util.Collection interface. It does not allow the use of duplicate elements and at max can accommodate only one null element.

A Stream is a sequence of objects that supports various methods which can be pipelined to produce the desired result.

Below are the various methods to convert Set to Stream.

  1. Using Collection.stream(): This method involves directly converting the Set to Stream using Collection.stream() method.

    Algorithm:

    1. Get the Set to be converted.
    2. Convert Set to Stream. This is done using Set.stream().
    3. Return/Print the Stream.




    // Java Program to convert
    // Set to Stream in Java 8
      
    import java.util.*;
    import java.util.stream.*;
    import java.util.function.*;
      
    class GFG {
      
        // Generic function to convert a set to stream
        private static <T> Stream<T> convertSetToStream(Set<T> set)
        {
            return set.stream();
        }
      
        // Main method
        public static void main(String args[])
        {
            // Create a set of String
            Set<Integer> setOfInteger = new HashSet<>(
                Arrays.asList(2, 4, 6, 8, 10));
      
            // Print the set of Integer
            System.out.println("Set of Integer: " + setOfInteger);
      
            // Convert Set of Stream
            Stream<Integer>
                streamOfInteger = convertSetToStream(setOfInteger);
      
            // Print the Stream of Integer
            System.out.println("Stream of Integer: "
                               + Arrays.toString(
                                 streamOfInteger.toArray()));
        }
    }

    Output:

    Set of Integer: [2, 4, 6, 8, 10]
    Stream of Integer: [2, 4, 6, 8, 10]
    
  2. Using Predicate to filter the Stream: In this method filter(Predicate) method is used that returns a stream consisting of elements that match the given predicate condition. The Functional Interface Predicate is defined in the java.util.Function package and can therefore be used as the assignment target for a lambda expression or method reference. It improves manageability of code, helps in unit-testing them separately

    Algorithm:

    1. Get the Set to be converted.
    2. Define the Predicate condition by either using pre-defined static methods or by creating a new method by overriding the Predicate interface. In this program, the interface is overridden to match the strings that start with “G”.
    3. Convert Set to Stream. This is done using Set.stream().
    4. Filter the obtained stream using the defined predicate condition
    5. The required Stream has been obtained. Return/Print the Stream.




    // Java Program to convert
    // Set to Stream in Java 8
      
    import java.util.*;
    import java.util.stream.*;
    import java.util.function.*;
      
    class GFG {
      
        // Generic function to convert a set to stream
        private static <T> Stream<T>
        convertSetToStream(Set<T> set, Predicate<T> predicate)
        {
            return set.stream()
                .filter(predicate);
        }
      
        // Main method
        public static void main(String args[])
        {
            // Create a set of String
            Set<String>
                setOfString = new HashSet<>(
                    Arrays.asList("GeeksForGeeks",
                                  "A computer portal",
                                  "for",
                                  "Geeks"));
      
            // Print the set of String
            System.out.println("Set of String: " + setOfString);
      
            // Create the predicate for item starting with G
            Predicate<String> predicate = new Predicate<String>() {
                @Override
                public boolean test(String s)
                {
                    // filter items that start with "G"
                    return s.startsWith("G");
                }
            };
      
            // Convert Set of Stream
            Stream<String>
                streamOfString = convertSetToStream(setOfString, predicate);
      
            // Print the filter Stream of String
            System.out.println("Stream from List with items"
                               + " starting with G: ");
      
            System.out.println(Arrays.toString(
                streamOfString.toArray()));
        }
    }

    Output:

    Set of String: [for, Geeks, GeeksForGeeks, A computer portal]
    Stream from List with items starting with G: 
    [Geeks, GeeksForGeeks]
    

Last Updated : 11 Dec, 2018
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