[Java]: Added static methods to get the headerSize for groups and var data. Enhancement aeron-io#92.

Author: mjpt777

main/java/uk/co/real_logic/sbe/generation/java/JavaGenerator.java

@@ -228,10 +228,9 @@ private void generateGroupClassHeader(final StringBuilder sb,
  indent + " blockLength = dimensions.blockLength();\n" +
  indent + " this.actingVersion = actingVersion;\n" +
  indent + " index = -1;\n" +
- indent + " parentMessage.limit(parentMessage.limit() + %d);\n" +
+ indent + " parentMessage.limit(parentMessage.limit() + headerSize());\n" +
  indent + " }\n\n",
- parentMessageClassName,
- dimensionHeaderSize
+ parentMessageClassName
  ));
 
  final Integer blockLength = Integer.valueOf(tokens.get(index).size());
@@ -249,12 +248,19 @@ private void generateGroupClassHeader(final StringBuilder sb,
  indent + " index = -1;\n" +
  indent + " this.count = count;\n" +
  indent + " blockLength = %4$d;\n" +
- indent + " parentMessage.limit(parentMessage.limit() + %5$d);\n" +
+ indent + " parentMessage.limit(parentMessage.limit() + headerSize());\n" +
  indent + " }\n\n",
  parentMessageClassName,
  javaTypeForNumInGroup,
  javaTypeForBlockLength,
- blockLength,
+ blockLength
+ ));
+
+ sb.append(String.format(
+ indent + " public static int headerSize()\n" +
+ indent + " {\n" +
+ indent + " return %d;\n" +
+ indent + " }\n\n",
  dimensionHeaderSize
  ));
 
@@ -285,7 +291,7 @@ private void generateGroupClassHeader(final StringBuilder sb,
  indent + " }\n\n" +
  indent + " public boolean hasNext()\n" +
  indent + " {\n" +
- indent + " return index + 1 < count;\n" +
+ indent + " return (index + 1) < count;\n" +
  indent + " }\n\n",
  formatClassName(groupName)
  ));
@@ -380,6 +386,16 @@ private CharSequence generateVarData(final List<Token> tokens)
  final ByteOrder byteOrder = lengthEncoding.byteOrder();
  final String byteOrderStr = lengthEncoding.primitiveType().size() == 1 ? "" : ", java.nio.ByteOrder." + byteOrder;
 
+ sb.append(String.format(
+ "\n" +
+ " public static int %sHeaderSize()\n" +
+ " {\n" +
+ " return %d;\n" +
+ " }\n",
+ toLowerFirstChar(propertyName),
+ sizeOfLengthField
+ ));
+
  sb.append(String.format(
  "\n" +
  " public int get%s(final byte[] dst, final int dstOffset, final int length)\n" +