optimized buffer handling and runtime optimization.

The initial buffer size is set to 10 characters, so it doesn't have to be increased that often.
If the buffer has to grow, just copy the identical pattern and not the whole string.

git-svn-id: https://svn.apache.org/repos/asf/lucene/java/trunk@170226 13f79535-47bb-0310-9956-ffa450edef68

src/java/org/apache/lucene/index/TermVectorsReader.java

@@ -241,22 +241,24 @@ class TermVectorsReader implements Cloneable {
     int start = 0;
     int deltaLength = 0;
     int totalLength = 0;
-    char [] buffer = {};
-    String previousString = "";
+    char [] buffer = new char[10];    // init the buffer with a length of 10 character
+    char[] previousBuffer = {};
     
     for (int i = 0; i < numTerms; i++) {
       start = tvf.readVInt();
       deltaLength = tvf.readVInt();
       totalLength = start + deltaLength;
-      if (buffer.length < totalLength)
-      {
+      if (buffer.length < totalLength) {  // increase buffer
+        buffer = null;    // give a hint to garbage collector
         buffer = new char[totalLength];
-        for (int j = 0; j < previousString.length(); j++)  // copy contents
-          buffer[j] = previousString.charAt(j);
+        
+        if (start > 0)  // just copy if necessary
+          System.arraycopy(previousBuffer, 0, buffer, 0, start);
       }
+      
       tvf.readChars(buffer, start, deltaLength);
       terms[i] = new String(buffer, 0, totalLength);
-      previousString = terms[i];
+      previousBuffer = buffer;
       int freq = tvf.readVInt();
       termFreqs[i] = freq;