8290300: Use standard String-joining tools where applicable

Reviewed-by: naoto, rriggs, dfuchs

src/java.base/share/classes/java/lang/ProcessBuilder.java

@@ -34,7 +34,6 @@
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
-import java.util.StringJoiner;
 import jdk.internal.event.ProcessStartEvent;
 import sun.security.action.GetPropertyAction;
 
@@ -1114,12 +1113,8 @@ private Process start(Redirect[] redirects) throws IOException {
                                      redirectErrorStream);
             ProcessStartEvent event = new ProcessStartEvent();
             if (event.isEnabled()) {
-                StringJoiner command = new StringJoiner(" ");
-                for (String s: cmdarray) {
-                    command.add(s);
-                }
                 event.directory = dir;
-                event.command = command.toString();
+                event.command = String.join(" ", cmdarray);
                 event.pid = process.pid();
                 event.commit();
             }

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

@@ -48,7 +48,6 @@
 import java.text.MessageFormat;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.spi.LocaleNameProvider;
-import java.util.stream.Collectors;
 
 import jdk.internal.vm.annotation.Stable;
 
@@ -2335,7 +2334,7 @@ private static String formatList(String[] stringList, String pattern) {
         // If we have no list patterns, compose the list in a simple,
         // non-localized way.
         if (pattern == null) {
-            return Arrays.stream(stringList).collect(Collectors.joining(","));
+            return String.join(",", stringList);
         }
 
         return switch (stringList.length) {

src/java.base/share/classes/sun/net/www/protocol/http/HttpURLConnection.java

@@ -1536,11 +1536,7 @@ private void setCookieHeader() throws IOException {
                         }
                         List<String> l = entry.getValue();
                         if (l != null && !l.isEmpty()) {
-                            StringJoiner cookieValue = new StringJoiner("; ");
-                            for (String value : l) {
-                                cookieValue.add(value);
-                            }
-                            requests.add(key, cookieValue.toString());
+                            requests.add(key, String.join("; ", l));
                         }
                     }
                 }

src/java.base/windows/classes/sun/nio/fs/WindowsPath.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008, 2021, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2008, 2022, 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
@@ -704,11 +704,9 @@ public WindowsPath subpath(int beginIndex, int endIndex) {
         if (beginIndex >= endIndex)
             throw new IllegalArgumentException();
 
-        StringBuilder sb = new StringBuilder();
+        StringJoiner sb = new StringJoiner("\\");
         for (int i = beginIndex; i < endIndex; i++) {
-            sb.append(elementAsString(i));
-            if (i != (endIndex-1))
-                sb.append("\\");
+            sb.add(elementAsString(i));
         }
         return new WindowsPath(getFileSystem(), WindowsPathType.RELATIVE, "", sb.toString());
     }