8356995: Provide default methods min(T, T) and max(T, T) in Comparator interface

src/java.base/share/classes/java/util/Comparator.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1997, 2021, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1997, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -30,7 +30,6 @@
 import java.util.function.ToIntFunction;
 import java.util.function.ToLongFunction;
 import java.util.function.ToDoubleFunction;
-import java.util.Comparators;
 
 /**
  * A comparison function, which imposes a <i>total ordering</i> on
@@ -189,6 +188,42 @@ default Comparator<T> reversed() {
         return Collections.reverseOrder(this);
     }
 
+    /**
+     * Returns the greater of two values according to this comparator.
+     * If the arguments are equal with respect to this comparator,
+     * the {@code b} argument is returned.
+     *
+     * @param   a   an argument.
+     * @param   b   another argument.
+     * @return  the larger of {@code a} and {@code b} according to this comparator.
+     * @throws  ClassCastException if the collection contains elements that are
+     *          not <i>mutually comparable</i> (for example, strings and
+     *          integers).
+     *
+     * @since 25
+     */
+    default T max(T a, T b) {
+        return compare(a, b) > 0 ? a : b;
+    }
+
+    /**
+     * Returns the smaller of two values according to this comparator.
+     * If the arguments are equal with respect to this comparator,
+     * the {@code a} argument is returned.
+     *
+     * @param   a   an argument.
+     * @param   b   another argument.
+     * @return  the smaller of {@code a} and {@code b} according to this comparator.
+     * @throws  ClassCastException if the collection contains elements that are
+     *          not <i>mutually comparable</i> (for example, strings and
+     *          integers).
+     *
+     * @since 25
+     */
+    default T min(T a, T b) {
+        return compare(a, b) > 0 ? b : a;
+    }
+
     /**
      * Returns a lexicographic-order comparator with another comparator.
      * If this {@code Comparator} considers two elements equal, i.e.

test/jdk/java/util/Comparator/MinMaxTest.java

@@ -0,0 +1,74 @@
+/*
+ * Copyright (c) 2025, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/**
+ * @test
+ * @bug 8356995
+ * @summary Comparator min/max method tests
+ * @run testng MinMaxTest
+ */
+
+import org.testng.annotations.Test;
+
+import java.util.Comparator;
+import static org.testng.Assert.*;
+
+@Test(groups = "unit")
+public class MinMaxTest {
+  public void testMin() {
+    Comparator<String> c = Comparator.naturalOrder();
+    assertEquals(c.min("a", "b"), "a");
+    assertEquals(c.min("b", "a"), "a");
+  }
+
+  public void testMax() {
+    Comparator<String> c = Comparator.naturalOrder();
+    assertEquals(c.max("a", "b"), "b");
+    assertEquals(c.max("b", "a"), "b");
+  }
+
+  public void testThrowsNPE() {
+    Comparator<String> c = Comparator.naturalOrder();
+    assertThrows(NullPointerException.class, () -> c.min(null, "a"));
+    assertThrows(NullPointerException.class, () -> c.min("a", null));
+    assertThrows(NullPointerException.class, () -> c.max(null, "a"));
+    assertThrows(NullPointerException.class, () -> c.max("a", null));
+  }
+
+  public void testThrowsCCE() {
+    @SuppressWarnings("unchecked")
+    Comparator<Object> c = (Comparator<Object>) (Comparator<?>)Comparator.naturalOrder();
+    assertThrows(ClassCastException.class, () -> c.min(1, "a"));
+    assertThrows(ClassCastException.class, () -> c.min("a", 1));
+    assertThrows(ClassCastException.class, () -> c.max(1, "a"));
+    assertThrows(ClassCastException.class, () -> c.max("a", 1));
+  }
+
+  public void testEqualReturnFirstOrLast() {
+    Comparator<Object> allEqual = (_, _) -> 0;
+    Object o1 = new Object();
+    Object o2 = new Object();
+    assertSame(allEqual.min(o1, o2), o1);
+    assertSame(allEqual.max(o1, o2), o2);
+  }
+}