Use a ArrayDeque and enable test only for JDK < 1.8

Author: gnodet

src/main/java/org/codehaus/plexus/util/xml/PrettyPrintXMLWriter.java

@@ -18,6 +18,8 @@
 
 import java.io.PrintWriter;
 import java.io.Writer;
+import java.util.ArrayDeque;
+import java.util.Deque;
 import java.util.LinkedList;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
@@ -35,7 +37,7 @@ public class PrettyPrintXMLWriter
 
     private PrintWriter writer;
 
-    private LinkedList<String> elementStack = new LinkedList<String>();
+    private final Deque<String> elementStack = new ArrayDeque<>();
 
     private boolean tagInProgress;
 
@@ -307,11 +309,6 @@ public void endElement()
         {
             finishTag();
 
-            // see issue #51: https://github.com/codehaus-plexus/plexus-utils/issues/51
-            // Rationale: replaced 1 write() with string concatenations with 3 write()
-            // (this avoids the string concatenation optimization bug detected in Java 7)
-            // TODO: change the below code to a more efficient expression when the library
-            // be ready to target Java 8.
             write( "</" );
             write( elementStack.removeLast() );
             write( ">" );
@@ -518,7 +515,7 @@ protected String getDocType()
     /**
      * @return the current elementStack;
      */
-    protected LinkedList<String> getElementStack()
+    protected Deque<String> getElementStack()
     {
         return elementStack;
     }

src/test/java/org/codehaus/plexus/util/xml/PrettyPrintXMLWriterTest.java

@@ -18,8 +18,9 @@
 
 import java.io.File;
 import java.io.IOException;
-import java.io.OutputStreamWriter;
 import java.io.StringWriter;
+import java.io.Writer;
+import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.util.NoSuchElementException;
 
@@ -28,6 +29,7 @@
 import org.codehaus.plexus.util.StringUtils;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Disabled;
 import org.junit.jupiter.api.Test;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
@@ -178,6 +180,7 @@ public void testendElementAlreadyClosed()
      *
      * @throws java.io.IOException if an I/O error occurs
      */
+    @Disabled( "This test is only relevant on JDK 1.7, which is not supported anymore" )
     @Test
     public void testIssue51DetectJava7ConcatenationBug()
         throws IOException
@@ -191,7 +194,7 @@ public void testIssue51DetectJava7ConcatenationBug()
 
         int iterations = 20000;
 
-        try ( OutputStreamWriter osw = new OutputStreamWriter( Files.newOutputStream( xmlFile.toPath() ), "UTF-8" ) )
+        try ( Writer osw = Files.newBufferedWriter( xmlFile.toPath(), StandardCharsets.UTF_8 ) )
         {
             writer = new PrettyPrintXMLWriter( osw );
             for ( int i = 0; i < iterations; ++i )