Convert Map to a Stream in Java

This post will discuss how to convert the map to a stream in Java.

1. Converting `Map<K,V>` to `Stream<Map.Entry<K,V>>`

We know that Map.entrySet() returns a set view of the mappings contained in this map. In Java 8, we can easily get a stream of key-value pairs, as shown below:

import java.util.Arrays;

import java.util.HashMap;

import java.util.Map;

import java.util.stream.Stream;

class Main

{

// Generic method to convert `Map<K, V>` to a stream of `<Map.Entry<K, V>`

private static <K, V> Stream<Map.Entry<K, V>> mapToStream (Map<K, V> map) {

return map.entrySet().stream();

}

// Program to convert map to a stream

public static void main(String[] args)

{

Map<String, Integer> asciiMap = new HashMap<>();

asciiMap.put("A", 65);

asciiMap.put("B", 66);

asciiMap.put("C", 67);

Stream<Map.Entry<String, Integer>> stream = mapToStream(asciiMap);

System.out.println(Arrays.toString(stream.toArray()));

}

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Output:

[A=65, B=66, C=67]

2. Converting `Map<K,V>` to `Stream<K>`

We can get a stream of keys of the map using Map.keySet() in Java 8 and above:

import java.util.Arrays;

import java.util.HashMap;

import java.util.Map;

import java.util.stream.Stream;

class Main

{

// Generic method to convert `Map<K, V>` to a `Stream<K>`

private static <K, V> Stream<K> mapToStream (Map<K, V> map) {

return map.keySet().stream();

}

// Program to convert map to a stream

public static void main(String[] args)

{

Map<String, Integer> asciiMap = new HashMap<>();

asciiMap.put("A", 65);

asciiMap.put("B", 66);

asciiMap.put("C", 67);

Stream<String> stream = mapToStream(asciiMap);

System.out.println(Arrays.toString(stream.toArray()));

}

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Output:

[A, B, C]

3. Converting `Map<K,V>` to `Stream<V>`

We can get a stream of values of the map using Map.values() in Java 8 and above:

import java.util.Arrays;

import java.util.HashMap;

import java.util.Map;

import java.util.stream.Stream;

class Main

{

// Generic method to convert `Map<K, V>` to a stream<V>

private static <K, V> Stream<V> mapToStream (Map<K, V> map) {

return map.values().stream();

}

// Program to convert map to a stream

public static void main(String[] args)

{

Map<String, Integer> asciiMap = new HashMap<>();

asciiMap.put("A", 65);

asciiMap.put("B", 66);

asciiMap.put("C", 67);

Stream<Integer> stream = mapToStream(asciiMap);

System.out.println(Arrays.toString(stream.toArray()));

}

Download Run Code

Output:

[65, 66, 67]

That’s all about converting Map to a Stream in Java.

Convert Map to a Stream in Java

1. Converting Map<K,V> to Stream<Map.Entry<K,V>>

2. Converting Map<K,V> to Stream<K>

3. Converting Map<K,V> to Stream<V>

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1. Converting `Map<K,V>` to `Stream<Map.Entry<K,V>>`

2. Converting `Map<K,V>` to `Stream<K>`

3. Converting `Map<K,V>` to `Stream<V>`