Program to convert a Set to Stream in Java using Generics
Last Updated :
11 Dec, 2018
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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.
- Using Collection.stream(): This method involves directly converting the Set to Stream using Collection.stream() method.
Algorithm:
- Get the Set to be converted.
- Convert Set to Stream. This is done using Set.stream().
- Return/Print the Stream.
Java // 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]
- 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:
- Get the Set to be converted.
- 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”.
- Convert Set to Stream. This is done using Set.stream().
- Filter the obtained stream using the defined predicate condition
- The required Stream has been obtained. Return/Print the Stream.
Java // 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]
