CPSC150 Spring 2007 Dr. L. Lambert

CPSC150 Overview Syllabus Use Textbook, ask questions, extra thorough, I will post sections covered All information and assignments posted on CPSC150 web page: –On web now, first homework For anything you don’t see on the web page, send me All grades posted on WebCT

Success in this Class Collaborative Come prepared to work in class Take notes; pay attention; ask questions Never procrastinate Don’t assume you know/can program easily Come see me/Java expert early and often Ask questions Consult with (possibly non-expert) peers, but be careful. >50% of your grade is exams. Make sure you are doing your own work before you take the exam

Success in the Department Join ACM, IEEE, SWE Study with others. –Right now, find others and exchange: major, contact information, one thing about you Sign up for department info. 1.open browser, go to 2.click on mailing lists, and students and careers 3.Subscribe using an address that you read regularly

Using Java and BlueJ We will use BlueJ for program development BlueJ runs on the Java virtual machine BlueJ is IDE – lots of others (e.g., Eclipse) BlueJ is free and available for Mac, Windows, UNIX Download BlueJ for your home machines for development: (download Java 1.5 first): (Download SDK, NOT JRE)

Next Steps Running Java Code Reading Java Code Writing Java Code

Running a program: BlueJ Demo: Shapes Classes - everything in BlueJ is a class Object Bench - holds objects in BlueJ Objects constructors - create an object Calling methods –makeVisible, changeSize, moveHorizontal Parameters: what info does method need?

Reading Source Code A Java program import package; // if any // comments and /* … */ and /** javadoc here */ public class Name { // instance variables or fields // visible to all methods in class // constructors. with no parameters is Default // methods } Look at: Circle source code

Parts of a Java program: Textbook 1.10 comments reserved words modifiers - public/private others statements blocks { } classes methods main method

Parts of a Java program: comments reserved words modifiers - public/private others statements blocks { } classes methods main method - not there. skip this Find in Circle source code

Writing a Program public class Sphere // in your code, put blank lines and {s on lines by themselves { private double radius; // instance var should always be private // other types: double, int, char, boolean, String (note capital), others public Sphere( ) { // constructor is named same as class name. radius = 1.0; } public Sphere(double myRadius) { // second constructor radius = myRadius; } // double is type that is returned public double calculateVolume( ) { double volume; // local variable. no private/public // = is assignment. this calculation is not quit right. why? volume = 4 / 3 * * radius * radius * radius; return volume; } }

Go to Mac lab or Use laptops Bring laptops to class

Write, Compile and Test Listing Figure 1.2, page 22 /** This program displays a message */ import javax.swing.JOptionPane; // case matters public class Message // begin classes with capital { // no variables in this program /** Constructor is named the same thing as class. In textbook, code is in main, and call to JOptionPane has another parameter. either is ok */ public Message( ) { JOptionPane.showMessageDialog(null, "Print your message here"); // or System.out.println("Print your message here"); on terminal }

Java program import package; // comments and /* … */ and /** javadoc here */ public class Name { // instance variables or fields // constructors. with no parameters is Default // methods }

Which are ok? public class ATestClass { /* A */ private int number; /* B. */ public int number; /* C. */ public Int number; /* D. */ private String name; /* E. */ String name; // constructor on next page } // keep the valid ones Create a class and type in the following. Which are ok? Compile. See what compiles. Why do the others not compile? Which compile, but are not ok?

Instance Variables What does the following do? public ATestClass ( ) { number = 3; //prints in terminal window System.out.println("number is " + number); String mystring = "this string"; name = "another string"; name = new String("A Third String"); System.out.println("name is " + name + "mystring is " + mystring + "); System.out.println(name + mystring); } 1.Add this constructor. Compile 2.Create an object. What happened? Why? 3.Inspect fields by right clicking, then choosing inspect 4.Change the names of the variables. What happens?

Class details: fields/instance variables private type name; –always private –name is lowercase (Classes are caps) Visible to all methods in class –local variables visible only to that method Can be primitive type or Object type

Primitive vs Objects private int myField; // primitive –char, boolean, double, int, a few others private Square wall; // Object type –user and library defined –look at Picture and inspect –primitive has data; object has pointer 1.Open Picture in Examples. Compile. Create a Picture object 2.Inspect wall field/instance variable 3.Add an integer field 4.Inspect it

Back to lecture

Java program import package; // comments and /* … */ and /** javadoc here */ public class Name { // instance variables or fields // constructors. with no parameters is Default // methods }

Class details: constructors Initialize objects. Called when object is created same name as class name no return type can be overloaded public Circle(int x, int y, int size, String startColor) { diameter = size; xPosition = x; yPosition = y; color = startColor; isVisible = false; } public Circle( ) { diameter = 30; xPosition = 20; yPosition = 60; color = "blue"; isVisible = false; }

public Circle(int x, int y, int size, String startColor) { diameter = size; xPosition = x; yPosition = y; color = startColor; isVisible = false; } public Circle( ) { diameter = 30; xPosition = 20; yPosition = 60; color = "blue"; isVisible = false; } 1.On the board, write a Circle constructor with a color parameter. call: new Circle("yellow"); 2.Write a variable declaration for Circle e. Create the circle using your new constructor. Circle c = new Circle( ); Circle d = new Circle(10, 20, 30, "green" );