diff --git a/src/java.base/share/classes/java/lang/String.java b/src/java.base/share/classes/java/lang/String.java
index b6e3805653a..4ec3e8b6a94 100644
--- a/src/java.base/share/classes/java/lang/String.java
+++ b/src/java.base/share/classes/java/lang/String.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1994, 2023, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1994, 2024, 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
@@ -841,7 +841,7 @@ public final class String
         }
         if (COMPACT_STRINGS) {
             byte[] val = StringUTF16.compress(ca, 0, caLen);
-            int coder = StringUTF16.coderFromArrayLen(val, len);
+            byte coder = StringUTF16.coderFromArrayLen(val, caLen);
             return new String(val, coder);
         }
         return new String(StringUTF16.toBytes(ca, 0, caLen), UTF16);
diff --git a/test/jdk/java/nio/file/Files/ReadWriteString.java b/test/jdk/java/nio/file/Files/ReadWriteString.java
index 885cbb771dc..8b5241fa1cf 100644
--- a/test/jdk/java/nio/file/Files/ReadWriteString.java
+++ b/test/jdk/java/nio/file/Files/ReadWriteString.java
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018, 2022, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2018, 2024, 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
@@ -29,8 +29,13 @@ import java.nio.charset.MalformedInputException;
 import java.nio.charset.UnmappableCharacterException;
 import static java.nio.charset.StandardCharsets.ISO_8859_1;
 import static java.nio.charset.StandardCharsets.US_ASCII;
-import static java.nio.charset.StandardCharsets.UTF_16;
 import static java.nio.charset.StandardCharsets.UTF_8;
+import static java.nio.charset.StandardCharsets.UTF_16;
+import static java.nio.charset.StandardCharsets.UTF_16BE;
+import static java.nio.charset.StandardCharsets.UTF_16LE;
+import static java.nio.charset.StandardCharsets.UTF_32;
+import static java.nio.charset.StandardCharsets.UTF_32BE;
+import static java.nio.charset.StandardCharsets.UTF_32LE;
 import java.nio.file.Files;
 import java.nio.file.OpenOption;
 import java.nio.file.Path;
@@ -40,15 +45,15 @@ import static java.nio.file.StandardOpenOption.CREATE;
 import java.util.Arrays;
 import java.util.Random;
 import java.util.concurrent.Callable;
+import static org.testng.Assert.assertEquals;
 import static org.testng.Assert.assertTrue;
 import static org.testng.Assert.fail;
-import org.testng.annotations.AfterClass;
 import org.testng.annotations.BeforeClass;
 import org.testng.annotations.DataProvider;
 import org.testng.annotations.Test;
 
 /* @test
- * @bug 8201276 8205058 8209576 8287541 8288589
+ * @bug 8201276 8205058 8209576 8287541 8288589 8325590
  * @build ReadWriteString PassThroughFileSystem
  * @run testng ReadWriteString
  * @summary Unit test for methods for Files readString and write methods.
@@ -61,6 +66,7 @@ public class ReadWriteString {
     // data for text files
     final String TEXT_UNICODE = "\u201CHello\u201D";
     final String TEXT_ASCII = "ABCDEFGHIJKLMNOPQRSTUVWXYZ\n abcdefghijklmnopqrstuvwxyz\n 1234567890\n";
+    final static String TEXT_PERSON_CART_WHEELING = "\ud83e\udd38";
     private static final String JA_STRING = "\u65e5\u672c\u8a9e\u6587\u5b57\u5217";
     private static final Charset WINDOWS_1252 = Charset.forName("windows-1252");
     private static final Charset WINDOWS_31J = Charset.forName("windows-31j");
@@ -154,7 +160,16 @@ public class ReadWriteString {
             {testFiles[1], TEXT_ASCII, US_ASCII, US_ASCII},
             {testFiles[1], TEXT_ASCII, US_ASCII, UTF_8},
             {testFiles[1], TEXT_UNICODE, UTF_8, null},
-            {testFiles[1], TEXT_UNICODE, UTF_8, UTF_8}
+            {testFiles[1], TEXT_UNICODE, UTF_8, UTF_8},
+            {testFiles[1], TEXT_ASCII, US_ASCII, ISO_8859_1},
+            {testFiles[1], TEXT_PERSON_CART_WHEELING, UTF_16, UTF_16},
+            {testFiles[1], TEXT_PERSON_CART_WHEELING, UTF_16BE, UTF_16BE},
+            {testFiles[1], TEXT_PERSON_CART_WHEELING, UTF_16LE, UTF_16LE},
+            {testFiles[1], TEXT_PERSON_CART_WHEELING, UTF_32, UTF_32},
+            {testFiles[1], TEXT_PERSON_CART_WHEELING, UTF_32BE, UTF_32BE},
+            {testFiles[1], TEXT_PERSON_CART_WHEELING, UTF_32LE, UTF_32LE},
+            {testFiles[1], TEXT_PERSON_CART_WHEELING, WINDOWS_1252, WINDOWS_1252},
+            {testFiles[1], TEXT_PERSON_CART_WHEELING, WINDOWS_31J, WINDOWS_31J}
         };
     }
 
@@ -304,6 +319,21 @@ public class ReadWriteString {
         throw new RuntimeException("An instance of " + expected + " should be thrown");
     }
 
+    // Verify File.readString with UTF16 to confirm proper string length and contents.
+    // A regression test for 8325590
+    @Test
+    public void testSingleUTF16() throws IOException {
+        String original = "🤸";    // "\ud83e\udd38";
+        Files.writeString(testFiles[0], original, UTF_16);
+        String actual = Files.readString(testFiles[0], UTF_16);
+        if (!actual.equals(original)) {
+            System.out.printf("expected (%s), was (%s)\n", original, actual);
+            System.out.printf("expected UTF_16 bytes: %s\n", Arrays.toString(original.getBytes(UTF_16)));
+            System.out.printf("actual UTF_16 bytes: %s\n", Arrays.toString(actual.getBytes(UTF_16)));
+        }
+        assertEquals(actual, original, "Round trip string mismatch with multi-byte encoding");
+    }
+
     private void checkNullPointerException(Callable<?> c) {
         try {
             c.call();