- Recall that the
meta data describes
the format of the
data
- Example 1:
- If the
format of the
data is:
The meta data will be:
- If the
format of the
data is:
- Example 2:
- If the
format of the
data is:
The meta data will be:
- If the
format of the
data is:
- Example 1:
- Important fact:
- We can use the meta data to access each record field according to the data type of that record field !!!
- Important fact about
(strongly typed) high level programming
language
(like Java):
- Every value has
a (data) type
Example:
- The data type of the value 3 is int
- The data type of the value "3" is String
- The data type of the value 3.0 is float
- And so on...
- Values of a
given data type
must be stored in
a variable of the
same data type
In other words:
- An int typed
value must be
stored in an int typed
variable
- A String typed
value must be
stored in an String typed
variable
- And so on.
(Otherwise, Java will perform conversion and you do not want that to happen !!!)
- An int typed
value must be
stored in an int typed
variable
- Every value has
a (data) type
- Suppose we are
reading the
first field of a record.
According to the previous discussion, we must do this:
- If the data type of
the field is
int:
- Read the int value and store it in an int typed variable
- If the data type of
the field is
String:
- Read the String value and store it in a String typed variable
- And so on.
- If the data type of
the field is
int:
- Important fact:
- You must use this method to read every field of the record !!!
- The following program fragment
illustrates
how to
use
the meta data
to read
one record from a
data file:
/* =========================================================== How to read ONE record USING the meta data ONE record has n_fields fields according to the Meta Data =========================================================== */ for ( int i = 0; i < n_fields; i++ ) { /* -------------------------------------------------------------- HOW you access the i-th field depends on the TYPE of the field ! -------------------------------------------------------------- */ if ( dataDes[i].fieldType.equals("I") ) { /* -------------------------------------------------------- Field i is an integer, use i_buf[i] to store the value -------------------------------------------------------- */ intVar = file.ReadInt( ); // Store in an int type var } else { /* -------------------------------------------------------- Field i is an String, use c_buf[i] to store the value -------------------------------------------------------- */ stringVar = in.nextLine(); // Store in a String type variable } }