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 email

• 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 www.pcs.cnu.edu2. click on mailing lists, and students and careers3. Subscribe using an email 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: www.bluej.org• (download Java 1.5 first):

http://java.sun.com/j2se/1.5.0/download.jsp (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 CodeA 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

commentsreserved wordsmodifiers - public/private othersstatementsblocks { }classesmethodsmain method

Parts of a Java program:

commentsreserved wordsmodifiers - public/private othersstatementsblocks { }classesmethodsmain method - not there. skip this

Find in Circle source code

Writing a Programpublic 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 * 3.14149 * 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 VariablesWhat 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" );