From 7e26e11295547efad14229111307091d49f541a8 Mon Sep 17 00:00:00 2001
From: JJ Brown <jack.brown.255@gmail.com>
Date: Sun, 12 Apr 2020 23:45:52 -0500
Subject: [PATCH] Provides optimized matchers for IsMapContaining.hasKey() and
 IsMapContaining.hasEntry(), which use the map's own containsKey(K key) method
 to avoid an O(n) worst-case linear search for every match.

This implements the change proposed in issue hamcrest/JavaHamcrest#172
---
 .../hamcrest/collection/IsMapContaining.java  | 65 ++++++++++++++++++-
 .../collection/IsMapContainingKeyTest.java    |  6 +-
 2 files changed, 65 insertions(+), 6 deletions(-)

diff --git a/hamcrest/src/main/java/org/hamcrest/collection/IsMapContaining.java b/hamcrest/src/main/java/org/hamcrest/collection/IsMapContaining.java
index 4ed45392..f4f79f3e 100644
--- a/hamcrest/src/main/java/org/hamcrest/collection/IsMapContaining.java
+++ b/hamcrest/src/main/java/org/hamcrest/collection/IsMapContaining.java
@@ -72,9 +72,32 @@ public static <K,V> Matcher<Map<? extends K,? extends V>> hasEntry(Matcher<? sup
      *     the value that, in combination with the key, must be describe at least one entry
      */
     public static <K,V> Matcher<Map<? extends K,? extends V>> hasEntry(K key, V value) {
-        return new IsMapContaining<>(equalTo(key), equalTo(value));
+        return new IsMapContainingEntry<>(key, value);
     }
-    
+
+    /**
+     * Provides a type-safe optimization over the O(n) linear search in {@link IsMapContaining#matchesSafely(Map)},
+     * by leveraging the speed of the map's own {@link Map#containsKey(Object)} check.
+     * <p>
+     * It preserves the same descriptors.
+     */
+    private static class IsMapContainingEntry<K, V> extends IsMapContaining<K, V>
+    {
+        private final K key;
+
+        public IsMapContainingEntry(K key, V value)
+        {
+            super(equalTo(key), equalTo(value));
+            this.key = key;
+        }
+
+        @Override
+        public boolean matchesSafely(Map<? extends K, ? extends V> map)
+        {
+            return map.containsKey(key) && super.valueMatcher.matches(map.get(key));
+        }
+    }
+
     /**
      * Creates a matcher for {@link java.util.Map}s matching when the examined {@link java.util.Map} contains
      * at least one key that satisfies the specified matcher.
@@ -98,7 +121,43 @@ public static <K,V> Matcher<Map<? extends K,? extends V>> hasEntry(K key, V valu
      *     the key that satisfying maps must contain
      */
     public static <K> Matcher<Map<? extends K, ?>> hasKey(K key) {
-        return new IsMapContaining<>(equalTo(key), anything());
+        return new IsMapContainingKey<>(key);
+    }
+
+    /**
+     * Provides a type-safe optimization over the O(n) linear search in {@link IsMapContaining#matchesSafely(Map)},
+     * by leveraging the speed of the map's own {@link Map#containsKey(Object)} check.
+     * <p>
+     * It preserves the same descriptors.
+     */
+    private static class IsMapContainingKey<K, V> extends IsMapContaining<K, V>
+    {
+        private final K key;
+
+        public IsMapContainingKey(K key)
+        {
+            super(equalTo(key), anything());
+            this.key = key;
+        }
+
+        @Override
+        public boolean matchesSafely(Map<? extends K, ? extends V> map)
+        {
+            return map.containsKey(key);
+        }
+
+        @Override
+        public void describeMismatchSafely(Map<? extends K, ? extends V> map, Description mismatchDescription)
+        {
+            mismatchDescription.appendText("map keys were ").appendValueList("[", ", ", "]", map.keySet());
+        }
+
+        @Override
+        public void describeTo(Description description)
+        {
+            description.appendText("map containing key ")
+                    .appendDescriptionOf(super.keyMatcher);
+        }
     }
 
     /**
diff --git a/hamcrest/src/test/java/org/hamcrest/collection/IsMapContainingKeyTest.java b/hamcrest/src/test/java/org/hamcrest/collection/IsMapContainingKeyTest.java
index 13f067c8..66876d0d 100644
--- a/hamcrest/src/test/java/org/hamcrest/collection/IsMapContainingKeyTest.java
+++ b/hamcrest/src/test/java/org/hamcrest/collection/IsMapContainingKeyTest.java
@@ -66,11 +66,11 @@ public void testMatchesMapContainingKeyWithNumberKeys() throws Exception {
     }
 
     public void testHasReadableDescription() {
-        assertDescription("map containing [\"a\"->ANYTHING]", hasKey("a"));
+        assertDescription("map containing key \"a\"", hasKey("a"));
     }
     
     public void testDoesNotMatchEmptyMap() {
-        assertMismatchDescription("map was []", hasKey("Foo"), new HashMap<String,Integer>());
+        assertMismatchDescription("map keys were []", hasKey("Foo"), new HashMap<String,Integer>());
     }
     
     public void testDoesNotMatchMapMissingKey() {
@@ -79,6 +79,6 @@ public void testDoesNotMatchMapMissingKey() {
         map.put("b", 2);
         map.put("c", 3);
         
-        assertMismatchDescription("map was [<a=1>, <b=2>, <c=3>]", hasKey("d"), map);
+        assertMismatchDescription("map keys were [\"a\", \"b\", \"c\"]", hasKey("d"), map);
     }
 }