BAEL-3091: The Prototype Pattern in Java (changed code based on valid comments from a reader)

java-collections-maps/src/main/java/com/baeldung/map/MapUtil.java

@@ -0,0 +1,44 @@
+/**
+ * 
+ */
+package com.baeldung.map;
+
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Set;
+import java.util.stream.Stream;
+
+/**
+ * @author swpraman
+ *
+ */
+public class MapUtil {
+    
+    public static <K, V> Stream<K> keys(Map<K, V> map, V value) {
+        return map.entrySet()
+                .stream()
+                .filter(entry -> value.equals(entry.getValue()))
+                .map(Map.Entry::getKey);
+    }
+    
+    public static <K, V> Set<K> getKeys(Map<K, V> map, V value) {
+        Set<K> keys = new HashSet<>();
+        for (Entry<K, V> entry : map.entrySet()) {
+            if (entry.getValue().equals(value)) {
+                keys.add(entry.getKey());
+            }
+        }
+        return keys;
+    }
+    
+    public static <K, V> K getKey(Map<K, V> map, V value) {
+        for (Entry<K, V> entry : map.entrySet()) {
+            if (entry.getValue().equals(value)) {
+                return entry.getKey();
+            }
+        }
+        return null;
+    }
+
+}