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]