Computer Science A 1: 3/2

Course plan• Introduction to programming• Basic concepts of typical programming

languages.• Tools: compiler, editor, integrated editor,

libraries.• A bit about software engineering –

methods used in constructing programs.• A bit about graphics• Freeware book

Computer Science AWhat you have to do

• 6 * home work

• 3 * mini-project

• 1 * oral test based on mini-project

All information available on http://akira.ruc.dk/~madsr/csa-f09.html

Java programspublic class Hello{ public static void main(String[] args){ System.out.println(”Hello world”); }}

A program contains classes (here Hello) chapters classes contains methods (here main) paragraphs methods contains statements (here System.out…)

One class has the same name as the file (Hello.java)One method in that class is called main

Java programsExtra spaces and newlines does not matter,

except:

• No newlines in text strings (”… ”)• At least one space between words (public static)

• Use indentations to make programs readable. The compiler ignores it, but I don’t

Case does matter String, class Hello and Hello.java

Java statementsPrint outSystem.out.println(….

Reading input…

Declare variablesint counter;

Change values of variablescounter = 1;

this can be combined into int counter = 1;Method callsif statementswhile statements

Expressions and valuesFor now: strings and numbers

String name=”Hello”;

int counter = 2;

(case does matter)

(three more types of values; some ways to construct more complex values from simple ones.)

Operations

+ on strings concatenate

+,-, *,/ on numbers add, subtract, multiply, divide

Assignmentint counter;

create a variable called counter

counter=1;

store the value 1 in the variable

counter=counter+1;

compute the value of the expression

counter+1 and store that in the variable.

counter now has the value 2

Inputinput via command prompt screen

java.util.Scanner in=

new java.util.Scanner(System.in);

System.out.println("type a name");

String line=in.nextLine();

System.out.println("type a number");

int num=in.nextInt();

System.out.println("read: "+line+" "+num);

Read a line and a number and save what you read in newly created variables

InputnextLine reads text until next linebreak, returns the text and

skips the linebreak

nextInt skips spaces and newlines until start of a number, it reads and returns the number

Notice that java and DOS does not read anything until you have finished a line. After a nextInt call the next symbol is probably a newline character.

Inputinput via dialog windows

String name= javax.swing.JOptionPane.showInputDialog( "type a name"); String num = javax.swing.JOptionPane.showInputDialog( "type a number");Output: javax.swing.JOptionPane.showMessageDialog( null,"read: "+name+" "+num); Read a line and a number and save what you read in newly

created variables

TextIO Eck has written his own class to do

Input/output. To use it you need to download it from his web page and place it in the same directory as your program.

To read a number write int num = TextIO.getlnInt();

To read a String write String s = TextIO.getln();

Java programspublic class Hello{ public static void main(String[] args){ System.out.println(”Hello world”); }}

Public: you can hide stuff from other parts of your program. Here: everything can be seen everywhere

static: some stuff may only exist for some of the time a program is executed. Here: it exists all the time

void: methods may return values. Here: it does not return anything.

String[] args: When you start a program it may have some command line arguments (you drop a file on a program etc). Here: it is not used.

Objects On Friday: expressions, variables etc

Eck chapter 2: 2.1 – 2.5 The important part is 2.1-2.3.2. The rest you can always look up when you need it