fix: implement toString, equals, hashCode for Key implementation used…

… in "of" (#11837) (#11875)

fixes #8474 and #4626

Co-authored-by: Denis <denis@vaadin.com>

flow-server/src/main/java/com/vaadin/flow/component/Key.java

@@ -20,6 +20,7 @@
 import java.util.Collections;
 import java.util.List;
 import java.util.Objects;
+import java.util.stream.Collectors;
 import java.util.stream.Stream;
 
 /**
@@ -2725,8 +2726,42 @@ static Key of(String key, String... additionalKeys) {
         List<String> keys = new ArrayList<>(additionalKeys.length + 1);
         keys.add(key);
         Collections.addAll(keys, additionalKeys);
-        List<String> unmodifiableKeyList = Collections.unmodifiableList(keys);
-        return () -> unmodifiableKeyList;
+        return new Key() {
+
+            @Override
+            public List<String> getKeys() {
+                return Collections.unmodifiableList(keys);
+            }
+
+            @Override
+            public String toString() {
+                List<String> keys = getKeys();
+                if (keys.size() == 1) {
+                    return keys.get(0);
+                }
+                return keys.get(0) + ",  additional keys : [" + keys.stream()
+                        .skip(1).collect(Collectors.joining(", ")) + "]";
+            }
+
+            @Override
+            public boolean equals(Object obj) {
+                if (obj == null) {
+                    return false;
+                }
+                if (obj == this) {
+                    return true;
+                }
+                if (!obj.getClass().equals(getClass())) {
+                    return false;
+                }
+                return getKeys().equals(((Key) obj).getKeys());
+            }
+
+            @Override
+            public int hashCode() {
+                return Objects.hash(getKeys());
+            }
+        };
     }
 
     /**

flow-server/src/test/java/com/vaadin/flow/component/KeyTest.java

@@ -15,6 +15,8 @@
  */
 package com.vaadin.flow.component;
 
+import java.util.Collections;
+import java.util.List;
 import java.util.concurrent.atomic.AtomicBoolean;
 
 import org.junit.Assert;
@@ -47,4 +49,60 @@ public void listenerWithMultipleKeyValues() {
         Assert.assertFalse(fired.get());
     }
 
+    @Test
+    public void of_toString_returnsKeys() {
+        Key key = Key.of("foo");
+
+        Assert.assertEquals("foo", key.toString());
+
+        key = Key.of("foo", "bar");
+
+        Assert.assertEquals("foo,  additional keys : [bar]", key.toString());
+    }
+
+    @Test
+    public void of_equals_stringRepresentationsEqual_toKeysAreEqual() {
+        Key key1 = Key.of("foo");
+        Key key2 = Key.of("foo");
+
+        Assert.assertEquals(key1, key2);
+    }
+
+    @Test
+    public void of_equals_stringRepresentationsNotEqual_toKeysAreNotEqual() {
+        Key key1 = Key.of("foo");
+        Key key2 = Key.of("bar");
+
+        Assert.assertNotEquals(key1, key2);
+    }
+
+    @Test
+    public void of_equals_secondKeyHasAdditionalKeys_toKeysAreNotEqual() {
+        Key key1 = Key.of("foo");
+        Key key2 = Key.of("foo", "bar");
+
+        Assert.assertNotEquals(key1, key2);
+    }
+
+    @Test
+    public void of_equals_differentClasses_toKeysAreNotEqual() {
+        Key key1 = Key.of("foo");
+        Key key2 = new Key() {
+
+            @Override
+            public List<String> getKeys() {
+                return Collections.singletonList("foo");
+            }
+        };
+
+        Assert.assertNotEquals(key1, key2);
+    }
+
+    @Test
+    public void of_equalKeys_hasSameHashCode() {
+        Key key1 = Key.of("foo", "bar");
+        Key key2 = Key.of("foo", "bar");
+        Assert.assertEquals(key1.hashCode(), key2.hashCode());
+    }
+
 }