Processing Large Files in Java, Variation 5

ReadFileJavaApplicationBufferedReader.diff45.java

--- ReadFileJavaApplicationBufferedReader4.java  2019-01-05 20:40:05.000000000 -0800
+++ ReadFileJavaApplicationBufferedReader5.java 2019-01-05 20:40:11.000000000 -0800
@@ -46,6 +46,8 @@
        ArrayList<String> firstNames = new ArrayList<>();
 
          var namePat = Pattern.compile(", \\s*([^, ]+)");
+         char[] chars = new char[6];
+         StringBuilder sb = new StringBuilder(7);
 
          System.out.println("Reading file using " + Caller.getName());
 
@@ -63,11 +65,12 @@
                  }
 
                String rawDate = array1[4].strip();
-               String month = rawDate.substring(4,6);
-               String year = rawDate.substring(0,4);
-               String formattedDate = month + "-" + year;
-               dates.add(formattedDate);
-
+                 rawDate.getChars(0, 6, chars, 0);
+                 sb.setLength(0);
+                 sb.append(chars, 0, 4)
+                   .append('-')
+                   .append(chars, 4, 2);
+                 dates.add(sb.toString());
        }
 
          for (int i : indexes) {