3.2 Java1492-plotting large quantities of data using java  (Page 7/27)

Usage information

The class provides a main method so that the class can be run as an application to test itself. The main method also illustrates how to use the class.

There are three steps involved in the use of this class for plotting large quantities of data:

1. Instantiate a plotting object of type PlotALot01 using one of two overloaded constructors.
2. Feed the data that is to be plotted to the plotting object by calling the feedData method once for each data value.
3. Call one of two overloaded plotData methods on the plotting object once all of the data has been fed to the object. This causesall of the data to be plotted and causes the pages to be stacked in a particular location on the screen with page 0 on the top of the stack.

Different plotting objects

A program that uses this class for plotting can instantiate as many different plotting objects as are needed to plot all of the different sets of data thatneed to be plotted independently of one another.

(For example, a program that uses this class could instantiate one plotting object to plot time series data and a different plotting object toplot spectral data.)

Can plot a large number of data values

Each plotting object can be used to plot as many data values as needed (unless the program runs out of memory) .

(As mentioned earlier, I have successfully plotted two million data values in 141 full screen pages on a modest laptop computer with nodifficulty whatsoever. When I pushed that total up to eight million data values in 563 full screen pages, the plotting process slowed down, but I wasstill able to display and examine the plots. The practical limit on my computer seems to be somewhere between two million and eight million datavalues.)

Multiple page objects

A plotting object of type PlotALot01 owns one or more Page objects that extend the Frame class. The plotting object can own as many Page objects as are necessary to plot all of the data that is fed to the plotting object.

A stack of page objects

The class produces a graphic output consisting of a stack of Page objects on the screen, with the data plotted on a Canvas object contained in each Page object. The Page showing the earliest data (page 0) is on the top of the stack and the Page showing the latest data is on the bottom of the stack.

(The Page objects on the top of the stack must be physically moved in order to see the Page objects further down in the stack.)

Multiple traces on each page object

As shown in Figure 1 , each Page object contains one or more horizontal axes on which the data is plotted. The earliest data is plotted onthe axis nearest the top of the Page moving from left to right across the Page . Positive data values are plotted above the axis and negative values are plotted below the axis.

When the right end of an axis is reached, the next data value is plotted on the left end of the axis immediately below it (sometimes referred to as wrap around) . When the right end of the last axis on the Page is reached, a new Page object is automatically created and the next data value is plotted at the left end of the top axis on the new Page object.