From ca20b8a82886aa74a57847be40152910c58fbdaf Mon Sep 17 00:00:00 2001
From: Tim Vernum <tim.vernum@elastic.co>
Date: Wed, 8 Apr 2020 15:31:50 +1000
Subject: [PATCH] Java8 implementation of Map.Entry (#54778)

A Java8 compatible version of Map.ofEntries() was added in #54183,
but it really needs a compat version of Map.entry as well in order to
facilitate easy backports from master.
---
 .../main/java/org/elasticsearch/common/collect/Map.java   | 8 ++++++++
 .../main/java11/org/elasticsearch/common/collect/Map.java | 7 +++++++
 .../java/org/elasticsearch/common/collect/MapTests.java   | 8 +++-----
 3 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/libs/core/src/main/java/org/elasticsearch/common/collect/Map.java b/libs/core/src/main/java/org/elasticsearch/common/collect/Map.java
index caa3aacd97f..3697f01abea 100644
--- a/libs/core/src/main/java/org/elasticsearch/common/collect/Map.java
+++ b/libs/core/src/main/java/org/elasticsearch/common/collect/Map.java
@@ -19,6 +19,7 @@
 
 package org.elasticsearch.common.collect;
 
+import java.util.AbstractMap;
 import java.util.Collections;
 import java.util.HashMap;
 
@@ -148,6 +149,13 @@ public class Map {
         }
     }
 
+    /**
+     * Returns an unmodifiable Map.Entry for the provided key and value.
+     */
+    public static <K, V> java.util.Map.Entry<K, V> entry(K k, V v) {
+        return new AbstractMap.SimpleImmutableEntry<>(k, v);
+    }
+
     /**
      * Returns an unmodifiable {@code Map} containing the entries of the given {@code Map}.
      *
diff --git a/libs/core/src/main/java11/org/elasticsearch/common/collect/Map.java b/libs/core/src/main/java11/org/elasticsearch/common/collect/Map.java
index f9badb14c2e..c213518ab2e 100644
--- a/libs/core/src/main/java11/org/elasticsearch/common/collect/Map.java
+++ b/libs/core/src/main/java11/org/elasticsearch/common/collect/Map.java
@@ -112,6 +112,13 @@ public class Map {
         return java.util.Map.ofEntries(entries);
     }
 
+    /**
+     * Delegates to the Java9 {@code Map.entry()} method.
+     */
+    public static <K, V> java.util.Map.Entry<K, V> entry(K k, V v) {
+        return java.util.Map.entry(k, v);
+    }
+
     /**
      * Delegates to the Java10 {@code Map.copyOf()} method.
      */
diff --git a/libs/core/src/test/java/org/elasticsearch/common/collect/MapTests.java b/libs/core/src/test/java/org/elasticsearch/common/collect/MapTests.java
index 84034fcbec4..49e92008988 100644
--- a/libs/core/src/test/java/org/elasticsearch/common/collect/MapTests.java
+++ b/libs/core/src/test/java/org/elasticsearch/common/collect/MapTests.java
@@ -21,8 +21,6 @@ package org.elasticsearch.common.collect;
 
 import org.elasticsearch.test.ESTestCase;
 
-import java.util.AbstractMap;
-
 import static org.hamcrest.CoreMatchers.equalTo;
 
 public class MapTests extends ESTestCase {
@@ -101,9 +99,9 @@ public class MapTests extends ESTestCase {
 
     public void testOfEntries() {
         final java.util.Map<String, Integer> map = Map.ofEntries(
-            new AbstractMap.SimpleEntry<>(numbers[0], 0),
-            new AbstractMap.SimpleEntry<>(numbers[1], 1),
-            new AbstractMap.SimpleEntry<>(numbers[2], 2)
+            Map.entry(numbers[0], 0),
+            Map.entry(numbers[1], 1),
+            Map.entry(numbers[2], 2)
         );
         validateMapContents(map, 3);
     }