JAVA BASICS

PROGRAM OUTPUT AND SOURCE CODE

• Overflow and underflow of numbers (i.e., Infinity and -Infinity),
• Arithmetic expressions where the result is not-a-number (i.e., NaN).

The last part of the program contains a looping contruct to evaluate a function y(x) that is designed to generate all three error conditions.

    4
    Red1  25   18  true
    Red2  25  -23  false
    Blue  03  123  true
    Green 13   03  false

    4
    Red1  25   18  true
    Red2  25  -23  false
    Blue  03  123  true
    Green 13   03  false

located at:

    http://www.isr.umd.edu/~austin/ence200.d/data.d/data.txt

From a software perspective, this program demonstrates use of functions and constants in the Math library, and simple decision making with an if() branching construct.

Input from the keyboard is handled by the method keyboardInput() and a character string sLine. Equivalent functionality can be achieved with the method getTextFromConsole().

From a software standpoint, this program demonstrates use of the if()-elseif()-else branching construct.

From a software standpoint, this program demonstrates use of the modulo arithmetic operator. The software implementation is simplified by organizing the code into methods: main() and windForce(). Notice how windForce accepts one argument of type double, and returns the wind force as a double.

The adjacent figure shows that line segments can be modeled by their two endpoints (i.e., with the classes Vector, Node and LineSegment).

The class Vector models two dimensional vectors characterised by (x,y) coordinate pairs. The class Node extends Vector. It adds a name. An edge line segment is characterised by its two "node" end points (i.e., The class Edge uses instances of class Node). Finally, the class Triangle uses three instances of class Node and three instances of class Edge.

    Circle.class        Location.class       TestShape.class
    Rectangle.class     Shape.class

This example creates and prints date objects in a variety of formats. It then shows how dates can be compared and incorporated into if-else statements.

You will need these routines if you are working with Java 1.3/1.4. In Java 1.5, much of the same functionality can be achieved with the System.out.printf(...) method.

Then the objects are added to an array list and printed by walking along the list. Notice how the toString() method in Person is used to print the abbreviated details of a person's credentials.

Finally, the person objects are ordered according to their age -- from youngest to oldest. Because an arraylist is a Collection, we can use the sort() method in Collections to take care of the details. All that we have to provide is a method to compare relative age of two person objects. These details can be found in Family.java.

Here is a very simple example. The fragment of code:

    SymbolTable st = new SymbolTable();
    st.put(   "mark", "acura" );
    st.put( "dianne",   "bmw" );

stores two entries in the symbol table, namely, that "mark drives an acura" and "dianne drives a bmw." To retrieve these records from the symbol table, we write something like:

    String s = "mark"
    System.out.println ( s + " drives a " + st.get(s) );
    String t = "dianne"
    System.out.println ( t + " drives a " + st.get(t) );

The example code creates a series of MetroStation objects, which are then stored in the symbol table. Then an array of "metro station names" are defined for the red and green lines. The corresponding metro station objects are retrieved from the symbol table, and the "line" attribute is added to the metro station object description. Some metro stations will service more than one metro line.

All of the source code is contained within a single file DemoGUI.java. The files before and after compilation are as follows:

    Before Compilatioon                           After Compilation
    ===============================================================
           DemoGUI.html                                DemoGUI.html
           DemoGUI.java                                DemoGUI.java
                                                 ButtonAction.class
                                                      DemoGUI.class
                                           DemoGraphicsScreen.class
                                             GraphicsListener.class
    ===============================================================

The buttons are positioned within a panel and connected to button listeners. A "border layout manager" is used to position the canvas in the center of the window and the panel along the South border.

A JAR file is simply a ZIP file that contains classes, possibly other files that a program may need (e.g., image and sound files), and a manifest file describing the special features of the archive.

This example demonstrates how java source code can be organized into packages, compiled, and then bundled into a jar file. The unpacked source code will be in a directory called packages-and-jar.d. Move to that directory and then read the file called README.txt.

To unpack the zip tar file, type:

    unzip PackagesAndJar.zip

The unpacked source code will be in a directory called packages-and-ant.d. Move to that directory and then read the file called README.txt.

To unpack the zip tar file, type:

    unzip PackagesAndAnt.zip

This program computes the distance of a point from the edge contour of a polygon.

Figure. Screendump of triangle and point program

The triangle is composed of three edges and three nodes. Each edge is simply a line segment. Hence, the problem of computing the closest distance to the edge of the triangle boils down to computing the distance of the point from each edge and then taking the minumum value. These computations can be found in Edge.java and Triangle.java, respectively.

To compile the program, type:

   javac DemoGUI.java

The program can be run as an applet. I just type:

   appletviewer DemoGUI.html

where DemoGUI.html is a suitable file containing a reference to the point-and-triangle bytecode files.

Many potentially difficult problems can be avoided by modeling the footprint as a collection of simple triangular regions. The next figure shows, for example, a six-triangle footprint model for the AV. Williams Building.

Figure. Footprint Model for AV Williams Building

Now let's move onto details of the software implementation.

Figure. Class Diagram for Footprint Implementation

Simply put, the adjacent figure says that one Footprint object will be composed of many Triangle objects. In turn, triangles will be defined in terms of Node and Edge objects. Nodes are an extension of Vector. Properties of the building footprint (e.g., area, center of mass) will be computed and summed across the ensemble of triangles.

To compile the program, type:

   javac Footprint.java

The program can be run as an application.

Figure. Cross Section Model of a Wheel.

In this specific example, the minumum radius is 50 and the maximum radius is 150. Coordinates in the radial and angular directions are divided into three and sixteen intervals, repectively. Theoretical considerations indicate that the cross section will be 62,831. However, because the triangles only approximate the circular cross section, the computed area will be a little less.

Individual triangle objects are assembled from Node and Edge objects, as shown above in the Footprint model. The wheel cross section is simply a collection of triangles stored in an array list.

The mesh of triangles in generated with a double loop. One loop increments the coordinates from the minumum radius to the maximum radius. A second loop systematically generates nodal coordiates in an angular direction, from 0.0 through 2*pi radians.

To compile the program, type:

   javac DemoWheel.java

The program can be run as an applet i.e.,

appletviewer DemoWheel.html

Figure. Screendump of bridge cross section and engineering properties ...

Polygon cross sections are modeled as an exterior ring, possible containing multiple interior rings. Each ring corresponds to a list of nodes have (x,y) coordinates. The nodes in an exterior ring are stored in a clockwise direction. Interior rings (holes) have nodes stored in an anti-clockwise direction.

Polygon cross sections are defined in an xml file. For example:

<?xml version="1.0" encoding="UTF-8"?>

<!-- Polygon Layout XML document -->
<!DOCTYPE polygon SYSTEM 'polygon.dtd'>

<polygon>
  <loop type="exterior">
        <coordinate>   100.0   0.0 </coordinate>
        <coordinate>   100.0 200.0 </coordinate>
        <coordinate>   300.0 200.0 </coordinate>
        <coordinate>   300.0   0.0 </coordinate>
  </loop>
</polygon>

defines a small square.

To unpack the tar file, type:

    tar xvf BridgeAnalysis.tar

The unpacked program will be in a directory called bridge-analysis.d. Move to that directory and then compile the program with the command:

    javac PolygonGUI.java

To run the program, type:

    appletviewer PolygonGUI.html

Figure. Screendump of Day Planner Application

The schedule of events in stored in an XML file called planner.xml. Here is an abbreviated snippet of code:

<?xml version="1.0" encoding="UTF-8"?>
<!-- Travel Planner XML document -->
<!DOCTYPE planner SYSTEM 'planner.dtd'>

<planner>
    <year value="2004">
        <date month="1" day="27">
            <note time="0000"> Last day to
                  cancel spring registration </note>
        </date>

        .... details of code removed ....

    </year>
</planner>

The following figure is a simplified model of the Washington DC metro system (most of the stations have been omitted):

Figure. Simplified View of the Washington DC Metro System

Passengers need to be familiar with the routes, schedule, and cost of using the metro. Typical questions include:

• When will the metro open? When will it close?
• How do I get from station A to station B?
• Will I have to change trains? Where?
• How long will it take to get there? And how must will it cost?
• I'm going to the Smithsonian -- what station should I get off?
• I'm at station A. When is the last train to station B?

The Smithsonian question is particularly interesting because: (1) it requires that a transportation model be linked to a geographic information systems (GIS) model, and (2) there really isn't a unique answer.

In its most rudimentary form, the Metro System can be modeled as a graph structure. Nodes in the graph correspond to train stations; the edges correspond to the tracks connecting stations. Graph theory is useful because it provides algorithms to answer questions about routes connecting stations A and B.

The adjacent code is a first-cut implementation at modeling this problem domain.

Question
How would you extend the basic node-edge graph structure to make the model more realistic.

Figure. Framework for Route Selection Problem

As indicated in the adjacent figure, this problem is complicated by the multitude of physical/.geographic, environmental, economic and political factors that can influence the final cost and efficiency of the system. Suppose, for example, that we want to build a road from city A to city B, but that a mountain range spans the most direct route. Is it better to build a road around the mountains, or pay more money upfront to build a tunnel through the mountains and provide a shorter route?

The standard approach to problems of this type is to deal with each concern separately, and then combine the results. For example, the physical constraints might look like:

Figure. Dealing with Physical Constraints in the Route Selection Problem

The final result is always never a single point, but rather a family of good solutions:

Figure. Pareto Optimal Curves