Program to convert a Map to a Stream in Java

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

Below are various method to convert Map to Stream in Java:

1. Converting complete Map<Key, Value> into Stream: This can be done with the help of Map.entrySet() method which returns a Set view of the mappings contained in this map. In Java 8, this returned set can be easily converted into a Stream of key-value pairs using Set.stream() method.

   Algorithm:

   1. Get the Map<Key, Value>.
   2. Convert Map<Key, Value> into Set<Key> using Map.entrySet() method.
   3. Convert the obtained Set into Stream using Set.stream()
   4. Return/Print the Stream of Map.

   Program:

   
   

   
   
   

   // Java Program to convert // Map<Key, Value> into Stream    import java.util.*; import java.util.stream.*;    class GFG {        // Generic function to convert List of     // String to List of Integer     public static <K, V> Stream<Map.Entry<K, V> >     convertMapToStream(Map<K, V> map)     {            // Return the obtained Stream         return map                // Convert the Map to Set             .entrySet()                // Convert the Set to Stream             .stream();     }        public static void main(String args[])     {            // Create a Map         Map<Integer, String> map = new HashMap<>();            // Add entries to the Map         map.put(1, "Geeks");         map.put(2, "forGeeks");         map.put(3, "A computer Portal");            // Print the Map         System.out.println("Map: " + map);            // Convert the Map to Stream         Stream<Map.Entry<Integer, String> > stream =                                     convertMapToStream(map);            // Print the TreeMap         System.out.println("Stream: "                        + Arrays.toString(stream.toArray()));     } }
   Output:

   Map: {1=Geeks, 2=forGeeks, 3=A computer Portal}
   Stream: [1=Geeks, 2=forGeeks, 3=A computer Portal]
   

2. Converting only the Keyset of the Map<Key, Value> into Stream: This can be done with the help of Map.keySet() method which returns a Set view of the keys contained in this map. In Java 8, this returned set can be easily converted into a Stream of key-value pairs using Set.stream() method.

   Algorithm:

   1. Get the Map<Key, Value>.
   2. Convert Map<Key, Value> into Set<Key> using Map.keySet() method.
   3. Convert the obtained Set into Stream using Set.stream()
   4. Return/Print the Stream of Map.

   Program:

   
   

   
   
   

   // Java Program to convert // Map<Key, Value> into Stream    import java.util.*; import java.util.stream.*;    class GFG {        // Generic function to convert List of     // String to List of Integer     public static <K, V> Stream<K>     convertMapToStream(Map<K, V> map)     {            // Return the obtained Stream         return map                // Convert the Map to Set<Key>             .keySet()                // Convert the Set to Stream             .stream();     }        public static void main(String args[])     {            // Create a Map         Map<Integer, String> map = new HashMap<>();            // Add entries to the Map         map.put(1, "Geeks");         map.put(2, "forGeeks");         map.put(3, "A computer Portal");            // Print the Map         System.out.println("Map: " + map);            // Convert the Map to Stream         Stream<Integer> stream = convertMapToStream(map);            // Print the TreeMap         System.out.println("Stream: "                      + Arrays.toString(stream.toArray()));     } }
   Output:

   Map: {1=Geeks, 2=forGeeks, 3=A computer Portal}
   Stream: [1, 2, 3]
   

3. Converting only the Value of the Map<Key, Value> into Stream: This can be done with the help of Map.values() method which returns a Set view of the values contained in this map. In Java 8, this returned set can be easily converted into a Stream of key-value pairs using Set.stream() method.

   Algorithm:

   1. Get the Map<Key, Value>.
   2. Convert Map<Key, Value> into Set<Value> using Map.values() method.
   3. Convert the obtained Set into Stream using Set.stream()
   4. Return/Print the Stream of Map.

   Program:

   
   

   
   
   

   // Java Program to convert // Map<Key, Value> into Stream    import java.util.*; import java.util.stream.*;    class GFG {        // Generic function to convert List of     // String to List of Integer     public static <K, V> Stream<V>     convertMapToStream(Map<K, V> map)     {            // Return the obtained Stream         return map                // Convert the Map to Set<Value>             .values()                // Convert the Set to Stream             .stream();     }        public static void main(String args[])     {            // Create a Map         Map<Integer, String> map = new HashMap<>();            // Add entries to the Map         map.put(1, "Geeks");         map.put(2, "forGeeks");         map.put(3, "A computer Portal");            // Print the Map         System.out.println("Map: " + map);            // Convert the Map to Stream         Stream<String> stream = convertMapToStream(map);            // Print the TreeMap         System.out.println("Stream: "                       + Arrays.toString(stream.toArray()));     } }
   Output:

   Map: {1=Geeks, 2=forGeeks, 3=A computer Portal}
   Stream: [Geeks, forGeeks, A computer Portal]