1005

cs 110 -- October 5 -- Review Session

Java, HTML and the WEB

Java is a programming language

good general purpose but gained popularity for being able to write program that could run on oher people's computers
such programs sit inside HTML (hyper text markup language) pages accessable via URL(uniform resource locators) and are called applets
HTML pages consist of text, images, and applets with formatting by TAGS.

<H1> <applet> <BODY> <img>

An <applet> tag tells the browser to run a program (a java applet) within the browser

<body> <applet code=MyCody.class width=400 height=500></applet></body>

code, height, width mean!!

Java is Object Oriented programming

class definition { everything inside }
idea is that you can use an object unchanged or modify it to suit your needs while easily using those parts that you do nt want to change

Java -- object is called class

classes have methods and class variables
classes start with a definition line

public class ClassName extends Applet implements ActionListener, AdjustmentListener

methods start with a definition line

public void methodName(param list)
names are always at your choice in definition line
methods are small subprograms

methods may have their own internal variables

predifined methods that you want to change the action of

overwrite

e.g., paint, init, adjustmentValueChanged, actionPerformed

new methods

you choose everything
params in "call" match up by position

public void a(int a, int b, int c) { }
a(10, 20, 30);

class variables have only a definiton line

private int variableName = 14;
=14 is optional

public/private/nothing in definition lines

describes who can access
public -- anyone can -- classes are almost always public
private -- no one outside the class can acceess -- classVariables are usually private but may be public or nothing
nothing -- somewhere in between public and private

int and float data types

int x = 5;
x = x / 3;
float y=5.0f;
y = y / 3;

Writing programs to be run inside of browsers

simple public class MyClass extends Applet

by "extending" Applet you mean that the program is intended to be run inside a browser

paint method

controls what will appear in applet
g.drawOval, g.fillOval, g.drawLine, g.drawString, g.drawRect, g.fillRect, g.drawArc, g.fillArc, g.setBackground

Widgets

init method
layout managers
widgets can talk but must also tell program to listen.
Scrollbar -- addAdjustmentListener, implements AdjustmentListener, public void adjustmentValueChanged(AdjustmentEvent ae)

Scrollbar s; s.getValue();

Button, TextField -- addActionListener, implementsActionListener, public void actionPerformed(ActionEvent ae)

TextField tt; tt.getText();

Label -- like drawString -- label l; l.setText();

boolean variables

like info or float, but can only be "true" or "false"
boolean goingUp = true;
relational operators: >, <, <=, <=, ==
combination operators: &&, ||

if-then-else

if (condition) { then stuff } [else { else stuff }]

loops

while (condition) {repeat until condition false }
for (int i=0; i<5; i++) { do 5 times }