Records

Records

A data record is a group of data fields that are related.

A data field is for example an article number, article size, production date etc.

In mathematics in particular, we are interested in the data fields that we name in the analysis as a table of values. A value table assigns a natural or real number with a constant difference between the numbers based on the specified rule (function) to the respective pair of values.

We have already seen the representation of a function. Now we would like to learn how to represent several functions in one coordinate system.

A plotter can manage multiple records. Each data record has its own values for color, drawing style, etc.

There are two ways of writing multiple functions in Java.

The first option is to call the "nextDataSet ()" method. When this method is called, a new data record is automatically created in Plotter. Subsequent calls to "add ()" are then automatically assigned to this new data record. The disadvantage is that we have to specify 10 loops for 10 functions, which is why this option can be confusing.

for(double x = -(Math.PI); x <= (Math.PI); x += 0.01) {

      plotter.add(x, Math.sin(x));

}

plotter.nextDataSet();

for(double x = -(Math.pi); x <= (Math.PI); x += 0.01) {

      plotter.add(x, Math.cos(x));

}

The data records can be addressed directly for a more compact solution. To do this you have to specify the name of the respective function as a data record. The following can then be derived from the above code.

In general, the following statements apply to the data records:

- At the beginning, the internal counter is set to 0. The associated data record applies, but is currently created after the first access.

- If you use the "nextDataSet ()" method to switch to a different data record, this other data record is considered to be current.

- If the "add ()" method is called without the name, the current data record is used and with the "add ()" method the value of the respective data record is assigned but is not seen as the current data record.

- If a addressed data record does not yet exist, it will be created.

- The saved data records are numbered and saved internally. The first function begins with 0. The subsequent functions are given the next larger integer as a position (the position must be free. Otherwise the next function is simply given the next largest free integer.).

The names that we have defined as naming are irrelevant when used. The names or names are only for the programmer and are for simplification. If we only want to draw a function, we do not have to enter a name.

A data record is represented internally by an instance of the class “DataObject”.

It essentially consists of a sequence of pairs of values (x, y). You can add or delete pairs of values using the following methods.

Method                                                                                       functionality

void add(double x, double y)                               appends the pair of values (x, y)

void addD(double dx, double dy)                          (x + dx, y + dy) is added from the last value (x, y).

void add(double[] feld)                                         appends all values from the given field

void removeOlt(int n)                                                                  deletes the first n values

In order to move all points of a data set together, offset values can be set for the x and y directions. With the four methods, the corresponding values can be set and queried again.

Later we will show this by being able to draw values offset side by side several times.

There is a variant of all these methods with the name of the data record as an additional parameter. Usually, however, the methods of the "Plotter" class are sufficient for all access to the "DataObject" instances.