doogfooding use String.join

Change-Id: If83b6421fc216aa54d3fd1edc9387b781d619861
Signed-off-by: Carsten Hammer <carsten.hammer@t-online.de>
Reviewed-on: https://git.eclipse.org/r/c/platform/eclipse.platform.debug/+/174182
Tested-by: Platform Bot <platform-bot@eclipse.org>
Reviewed-by: Alexander Kurtakov <akurtako@redhat.com>
diff --git a/org.eclipse.unittest.ui/src/org/eclipse/unittest/internal/UnitTestPreferencesConstants.java b/org.eclipse.unittest.ui/src/org/eclipse/unittest/internal/UnitTestPreferencesConstants.java
index 1afcd46..2d043f0 100644
--- a/org.eclipse.unittest.ui/src/org/eclipse/unittest/internal/UnitTestPreferencesConstants.java
+++ b/org.eclipse.unittest.ui/src/org/eclipse/unittest/internal/UnitTestPreferencesConstants.java
@@ -55,14 +55,7 @@
 		if (list == null)
 			return ""; //$NON-NLS-1$
 
-		StringBuilder buffer = new StringBuilder();
-		for (int i = 0; i < list.length; i++) {
-			if (i > 0)
-				buffer.append(',');
-
-			buffer.append(list[i]);
-		}
-		return buffer.toString();
+		return String.join(String.valueOf(','), list);
 	}
 
 	/**