6356745: (coll) Add PriorityQueue(Collection, Comparator)

Co-authored-by: Valeh Hajiyev <valeh.hajiyev@gmail.com>
Reviewed-by: vklang, smarks, liach

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

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2003, 2025, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2003, 2026, 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
@@ -209,6 +209,32 @@ public class PriorityQueue<E> extends AbstractQueue<E>
         }
     }
 
+    /**
+     * Creates a {@code PriorityQueue} containing the elements in the
+     * specified collection. The elements of the new {@code PriorityQueue}
+     * will be ordered according to the specified comparator.
+     *
+     * @param  c the collection whose elements are to be placed
+     *         into this priority queue
+     * @param  comparator the comparator that will be used to order this
+     *         priority queue.  If {@code null}, the {@linkplain Comparable
+     *         natural ordering} of the elements will be used.
+     * @throws NullPointerException if the specified collection or any
+     *         of its elements are null
+     * @since 28
+     */
+    public PriorityQueue(Collection<? extends E> c,
+                         Comparator<? super E> comparator) {
+        this.comparator = comparator;
+        if (c instanceof SortedSet<? extends E> ss && comparator == ss.comparator()) {
+            initElementsFromCollection(ss);
+        } else if (c instanceof PriorityQueue<? extends E> pq && comparator == pq.comparator()) {
+            initFromPriorityQueue(pq);
+        } else {
+            initFromCollection(c);
+        }
+    }
+
     /**
      * Creates a {@code PriorityQueue} containing the elements in the
      * specified priority queue.  This priority queue will be

test/jdk/java/util/concurrent/tck/PriorityQueueTest.java

@@ -40,6 +40,7 @@ import java.util.Iterator;
 import java.util.NoSuchElementException;
 import java.util.PriorityQueue;
 import java.util.Queue;
+import java.util.TreeSet;
 
 import junit.framework.Test;
 
@@ -168,6 +169,101 @@ public class PriorityQueueTest extends JSR166TestCase {
             mustEqual(items[i], q.poll());
     }
 
+    /**
+     * Queue contains all elements of collection used to initialize and
+     * uses the custom comparator provided to order its elements
+     */
+    public void testConstructor8() {
+        Item[] items = seqItems(SIZE);
+        MyReverseComparator cmp = new MyReverseComparator();
+        @SuppressWarnings("unchecked")
+        PriorityQueue<Item> q = new PriorityQueue<>(Arrays.asList(items), cmp);
+        assertEquals(cmp, q.comparator());
+        for (int i = SIZE - 1; i >= 0; --i)
+            mustEqual(items[i], q.poll());
+    }
+
+    /**
+     * Initializing from Collection with a comparator has the order
+     * of its elements the same as the queue initialized with a comparator
+     * and populated with Collection after initialization
+     */
+    public void testConstructor9() {
+        Item[] items = seqItems(SIZE);
+        MyReverseComparator cmp = new MyReverseComparator();
+        @SuppressWarnings("unchecked")
+        PriorityQueue<Item> q1 = new PriorityQueue<>(Arrays.asList(items), cmp);
+        @SuppressWarnings("unchecked")
+        PriorityQueue<Item> q2 = new PriorityQueue<>(SIZE, cmp);
+        q2.addAll(Arrays.asList(items));
+        for (int i = 0; i < SIZE; ++i)
+            mustEqual(q1.poll(), q2.poll());
+    }
+
+    /**
+     * Initializing from null Collection throws NPE
+     */
+    public void testConstructor10() {
+        try {
+            new PriorityQueue<Item>((Collection<Item>)null, new MyReverseComparator());
+            shouldThrow();
+        } catch (NullPointerException success) {}
+    }
+
+    /**
+     * Initializing from Collection of null elements throws NPE
+     */
+    public void testConstructor11() {
+        try {
+            new PriorityQueue<Item>(Arrays.asList(new Item[SIZE]), new MyReverseComparator());
+            shouldThrow();
+        } catch (NullPointerException success) {}
+    }
+
+    /**
+     * Initializing from PriorityQueue and its comparator
+     */
+    public void testConstructor12() {
+        Item[] items = seqItems(SIZE);
+        MyReverseComparator cmp = new MyReverseComparator();
+        @SuppressWarnings("unchecked")
+        PriorityQueue<Item> q1 = new PriorityQueue<>(cmp);
+        q1.addAll(Arrays.asList(items));
+        @SuppressWarnings("unchecked")
+        PriorityQueue<Item> q2 = new PriorityQueue<>(q1, q1.comparator());
+        for (int i = 0; i < SIZE; ++i)
+            mustEqual(q1.poll(), q2.poll());
+    }
+
+    /**
+     * Initializing from SortedSet and its comparator
+     */
+    public void testConstructor13() {
+        Item[] items = seqItems(SIZE);
+        MyReverseComparator cmp = new MyReverseComparator();
+        @SuppressWarnings("unchecked")
+        TreeSet<Item> s = new TreeSet<>(cmp);
+        s.addAll(Arrays.asList(items));
+        @SuppressWarnings("unchecked")
+        PriorityQueue<Item> q = new PriorityQueue<>(s, s.comparator());
+        for (int i = 0; i < SIZE; ++i)
+            mustEqual(q.poll(), s.removeFirst());
+    }
+
+    /**
+     * Initializing with null comparator
+     */
+    public void testConstructor14() {
+        Item[] items = seqItems(SIZE);
+        @SuppressWarnings("unchecked")
+        PriorityQueue<Item> q1 = new PriorityQueue<>((Comparator<Item>) null);
+        q1.addAll(Arrays.asList(items));
+        @SuppressWarnings("unchecked")
+        PriorityQueue<Item> q2 = new PriorityQueue<>(Arrays.asList(items), null);
+        for (int i = 0; i < SIZE; ++i)
+            mustEqual(q1.poll(), q2.poll());
+    }
+
     /**
      * isEmpty is true before add, false after
      */