Program to Convert List to Stream in Java

11 Dec, 2018
The List is a child interface of Collection. It is an ordered collection of objects in which duplicate values can be stored. Since List preserves the insertion order, it allows positional access and insertion of elements. List Interface is implemented by ArrayList, LinkedList, Vector and Stack classes.
A Stream is a sequence of objects that supports various methods which can be pipelined to produce the desired result.
Below are various methods to convert List to Stream in Java:
Using List.stream() method: Java List interface provides stream() method which returns a sequential Stream with this collection as its source.Syntax:List.stream()Algorithm:Get the StreamConvert Stream into List using List.stream() method.Return the ListProgram:// Java Program to convert// List to Stream in Java 8  import java.util.*;import java.util.stream.*;import java.util.function.Function;  class GFG {      // Generic function to convert a list to stream    private static <T> Stream<T> convertListToStream(List<T> list)    {        return list.stream();    }      public static void main(String args[])    {          // Create a stream of integers        List<String> list = Arrays.asList("GeeksForGeeks",                                          "A computer portal",                                           "for Geeks");          // Print the List        System.out.println("List: " + list);          // Convert List to stream        Stream<String> stream = convertListToStream(list);          // Print the Stream        System.out.println("Stream from List: "                    + Arrays.toString(stream.toArray()));    }}Output:List: [GeeksForGeeks, A computer portal, for Geeks]
Stream from List: [GeeksForGeeks, A computer portal, for Geeks]
Filter Stream using a Predicate: 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 separatelyAlgorithm:Get the StreamDefine 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 Stream into List using List.stream() method.Filter the obtained stream using the defined predicate conditionThe required Stream has been obtained.Hence Print the filtered elements of the Stream using forEach() method.It can also be returned as required.Program:// Java Program to convert// List to Stream in Java 8  import java.util.*;import java.util.stream.*;import java.util.function.*;  class GFG {      public static void main(String args[])    {          // Create a stream of integers        List<String> list = Arrays.asList("GeeksForGeeks",                                          "A computer portal",                                           "for",                                           "Geeks");          // Print the List        System.out.println("List: " + list);          // 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");            }        };          System.out.println("Stream from List with items"+                                      " starting with G: ");          // Convert List to stream        list.stream()            .filter(predicate)            .forEach(System.out::println);    }}Output:List: [GeeksForGeeks, A computer portal, for, Geeks]
Stream from List with items starting with G: 
GeeksForGeeks
Geeks

Using List.stream() method: Java List interface provides stream() method which returns a sequential Stream with this collection as its source.Syntax:List.stream()Algorithm:Get the StreamConvert Stream into List using List.stream() method.Return the ListProgram:// Java Program to convert// List to Stream in Java 8  import java.util.*;import java.util.stream.*;import java.util.function.Function;  class GFG {      // Generic function to convert a list to stream    private static <T> Stream<T> convertListToStream(List<T> list)    {        return list.stream();    }      public static void main(String args[])    {          // Create a stream of integers        List<String> list = Arrays.asList("GeeksForGeeks",                                          "A computer portal",                                           "for Geeks");          // Print the List        System.out.println("List: " + list);          // Convert List to stream        Stream<String> stream = convertListToStream(list);          // Print the Stream        System.out.println("Stream from List: "                    + Arrays.toString(stream.toArray()));    }}Output:List: [GeeksForGeeks, A computer portal, for Geeks]
Stream from List: [GeeksForGeeks, A computer portal, for Geeks]

Syntax:
List.stream()
Algorithm:
Get the StreamConvert Stream into List using List.stream() method.Return the List
Get the Stream
Convert Stream into List using List.stream() method.
Return the List
Program:
// Java Program to convert// List to Stream in Java 8  import java.util.*;import java.util.stream.*;import java.util.function.Function;  class GFG {      // Generic function to convert a list to stream    private static <T> Stream<T> convertListToStream(List<T> list)    {        return list.stream();    }      public static void main(String args[])    {          // Create a stream of integers        List<String> list = Arrays.asList("GeeksForGeeks",                                          "A computer portal",                                           "for Geeks");          // Print the List        System.out.println("List: " + list);          // Convert List to stream        Stream<String> stream = convertListToStream(list);          // Print the Stream        System.out.println("Stream from List: "                    + Arrays.toString(stream.toArray()));    }}
List: [GeeksForGeeks, A computer portal, for Geeks]
Stream from List: [GeeksForGeeks, A computer portal, for Geeks]

Filter Stream using a Predicate: 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 separatelyAlgorithm:Get the StreamDefine 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 Stream into List using List.stream() method.Filter the obtained stream using the defined predicate conditionThe required Stream has been obtained.Hence Print the filtered elements of the Stream using forEach() method.It can also be returned as required.Program:// Java Program to convert// List to Stream in Java 8  import java.util.*;import java.util.stream.*;import java.util.function.*;  class GFG {      public static void main(String args[])    {          // Create a stream of integers        List<String> list = Arrays.asList("GeeksForGeeks",                                          "A computer portal",                                           "for",                                           "Geeks");          // Print the List        System.out.println("List: " + list);          // 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");            }        };          System.out.println("Stream from List with items"+                                      " starting with G: ");          // Convert List to stream        list.stream()            .filter(predicate)            .forEach(System.out::println);    }}Output:List: [GeeksForGeeks, A computer portal, for, Geeks]
Stream from List with items starting with G: 
GeeksForGeeks
Geeks

Algorithm:
Get the StreamDefine 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 Stream into List using List.stream() method.Filter the obtained stream using the defined predicate conditionThe required Stream has been obtained.Hence Print the filtered elements of the Stream using forEach() method.It can also be returned as required.
Get the Stream
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 Stream into List using List.stream() method.
Filter the obtained stream using the defined predicate condition
The required Stream has been obtained.Hence Print the filtered elements of the Stream using forEach() method.It can also be returned as required.
Program:
// Java Program to convert// List to Stream in Java 8  import java.util.*;import java.util.stream.*;import java.util.function.*;  class GFG {      public static void main(String args[])    {          // Create a stream of integers        List<String> list = Arrays.asList("GeeksForGeeks",                                          "A computer portal",                                           "for",                                           "Geeks");          // Print the List        System.out.println("List: " + list);          // 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");            }        };          System.out.println("Stream from List with items"+                                      " starting with G: ");          // Convert List to stream        list.stream()            .filter(predicate)            .forEach(System.out::println);    }}
List: [GeeksForGeeks, A computer portal, for, Geeks]
Stream from List with items starting with G: 
GeeksForGeeks
Geeks

Java - util package
java-list
Java-List-Programs
java-stream
Java-Stream-programs
Java
Java Programs
Java
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