week 11

today's material :
- event listener
listener is needed to make a button do something when clicked
using method addActionListener

here's the code...
learn from this and the java api...

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.FlowLayout;
import java.awt.GridLayout;
import java.awt.Label;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.JTextField;


public class EventListener extends JFrame implements ActionListener{

JButton ok;
JButton cancel;
JButton add;
JTextField text;
JTextArea area;
String content;

public EventListener(){
setSize(640, 480);
setTitle("Simple Frame");
setDefaultCloseOperation(EXIT_ON_CLOSE);

setVisible(true);

ok = new JButton("OK");
ok.addActionListener(this);

cancel = new JButton("Cancel");
cancel.addActionListener(this);

add = new JButton("Add to List");
add.addActionListener(this);

text = new JTextField(15);
area = new JTextArea();

JPanel pnlSouth = new JPanel(new GridLayout(2, 1));
JPanel pnlNorth = new JPanel(new FlowLayout());

JPanel pnl1 = new JPanel(new FlowLayout());
JPanel pnl2 = new JPanel(new FlowLayout());

pnlNorth.add(new Label("Customer List"));
pnlNorth.setBackground(Color.LIGHT_GRAY);

pnlSouth.add(pnl1);
pnlSouth.add(pnl2);
pnlSouth.setBackground(Color.LIGHT_GRAY);

pnl1.add(text);
pnl1.add(add);

pnl2.add(ok);
pnl2.add(cancel);

getContentPane().add(pnlNorth , BorderLayout.NORTH);
getContentPane().add(pnlSouth , BorderLayout.SOUTH);
getContentPane().add(area);
}


public static void main(String[] args) {
EventListener frame = new EventListener();
}

public void actionPerformed(ActionEvent e) {
if(e.getSource() == ok){
JOptionPane.showMessageDialog(this, "Button OK Clicked");
}
if(e.getSource() == cancel){
JOptionPane.showMessageDialog(this, "Button Cancel Clicked");
}
if(e.getSource() == add){
content = content + "\n" + text.getText();
area.setText(content);
}
}
}


thats all..............

week11 - starting GUI

its week 11 already..
one step further, Graphical User Interface we were taught...
here, this is what i got..

Graphical User Interface
- in java, GUI used by including classes from javax.swing and java.awt packages
- java.awt is the oldest type of GUI
- different from VB and Delphi, java's GUI can be used in wide selection of OS

Subclassing JFrame
- first step using GUI : making frame
- frame consist of : title, size[in pixel]

Trying out
-
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.FlowLayout;
import java.awt.HeadlessException;
import javax.swing.*;
public class MySimpleFrame extends JFrame{

public MySimpleFrame() throws HeadlessException{
// setting the size of the frame
setSize(300, 200);

// setting the title of the frame
setTitle("My Simple Frame");

// setting the location of the frame
setLocation(100, 200);
// or
setLocationRelativeTo(null);

// setting the background color
getContentPane().setBackground(Color.blue);

// sets to terminate the program when the frame is closed
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

// initializing button 'ok'
JButton ok = new JButton();
ok.setSize(getMinimumSize());
ok.setText("OK");
ok.setBackground(Color.red);

// initializing button 'cancel'
JButton cancel = new JButton();
cancel.setSize(getMinimumSize());
cancel.setText("Cancel");
cancel.setBackground(Color.red);

// setting panel consist of button 'ok' and 'cancel'
JPanel pnlSouth = new JPanel(new FlowLayout());
add(pnlSouth, BorderLayout.SOUTH);
pnlSouth.setBackground(Color.BLACK);
pnlSouth.add(ok);
pnlSouth.add(cancel);

// makes the frame visible
setVisible(true);
}

public static void main(String[] args) {
MySimpleFrame msf = new MySimpleFrame();
}
}

i've put everything new with comment above it...
so it would be easy to learn from the code only...

that's all....

ciao...

week 10

what i learn today :

array, which includes :
- array initialization
- array usage
- array in both 1 dimension and 2 dimensions
- array of objects

collections, which includes :
- arraylist
- hashset
- iteration

basic input output :
- how to write / save a file
- how to read from an exisiting file

thats all...

week 9

back programming now...
its been 2 weeks...

here's what i got today..

characters and string

try this code
import javax.swing.*;
public class W09Chars {
public static void main(String[] args) {
char ch = 'Z';
byte b = 65;

JOptionPane.showMessageDialog(null, "ASCII code of character " + ch +
" is " + (int)ch);
JOptionPane.showMessageDialog(null, "Character with ASCII code " + b +
" is " + (char)b);
JOptionPane.showMessageDialog(null, ch + " is "
+ ((ch > b) ? "bigger" : "smaller")
+ " than " + (char)b);
}
}

highlight
((ch > b) ? "bigger" : "smaller")
same as
if(ch > b)
"bigger";
else
"smaller"

each character has a code in hexadecimal, which will be shown if the code is ran

back to topic,
character is a single digit while string is array consists of characters

comparing strings
case a : reffering to the same object
String word1 = "Surabaya"
String word2 = word1
both variable reffers to the same object, so
word1 == word2 is true
word1.equals(word2) is true
case b : reffering to different but identical object
String word1 = "Surabaya"
String word2 = new String("Surabaya")
which make
word1 == word2 is false, bacause the address is not the same
word1.equals(word2) is true, because the value is identical
case c : diferent value, different object

pattern matching
sometimes its needed to use a pattern
example 17-08-1945
the regular expression is:
[0-3][0-9]-[0-1][0-9]-[0-9]{4}

string buffer
needed because string is immutable or unchangable
any modification will produce new string
which will use more and more memory


thats all..

weeK 6

menu :
- this keyword
- his keyword
- overloading and overriding
- polymorphism
- variable and method scoping
- parameter passing
- package

custom java class
- modifying string, int, calendar, array, we can do it by using existing classes
- when we found another unique entity, we need to custom a class

using THIS keyword
- THIS adalah reference ke variable yang ada pada object itu sendiri
- dengan kata lain THIS adalah self referencing pointer

THIS using example
public class Rectangle{
private double length;
private double width;

public Rectangle(){

}
public void setLength(double length){
this.length = length;
}
public void setWidth(double width){
this.width = width;
}
}

examine this following snippet
- Rectangle kotak = new Rectangle()
- Rectangle is class method, owned by class, no need for isntantiation
- to use : Rectangle.ClassMethod();
- kotak = object, the instance method, owned by instance, need instantiation to use
- to use : kotak.InstanceMethod();

to make an instance method
- public static double compute(double length, double width)
- by adding static there
- need argument, it cant use a variable from the object

overloaded method
- is when methods with same name, is made with different signature
- example, the method print
- print can do it for many kinds

multiple constructors
- using THIS in a constructor means its calling other constructor
- ex :
public Rectangle(){
this(0., 0.);
}
public Rectangle(double length){
this(length, length);
}
public Rectangle(double length, double width){
setLength(length);
setWidth(width);
}
- the first Rectangle calls the second, and the second call the third

static initializers
- make the code get executed when a java class is loaded into the java system
- ex :
public class Point {
private static long x , y ;

static{
x = System.currentTimeMillis();
y = ++x;
}

public Point() {}
public static long getXY(){
return x+y;
}
}
- the code inside static is executed firstly after the class is loaded

overriding
- modify the behaviour of superclass method by rewriting it in the subclass
- tehe signature must exactly be the same
- ex :
public class Box extends Rectangle{
private double height;

public Box(){
this(0. , 0. , 0.);
}
public Box(double length, double width, double height){
super(length, width);
this.height = height;
}
public Box(double size){
this(size, size, size);
}
- Box is the subclass of Rectangle
- using THIS called the variable in that class
- using SUPER called the variable in its superclass

polymorphism
- where there are more classes extending from one including the superclass,
and most used as a bridge to get a value from its method
- ex :
public class TestShapes {
public static void main(String[] args) {
Rectangle square, dice, brick, rectangle;

square = new Rectangle(4. );
dice = new Box(3. );
brick = new Box(4. ,3. , 2.);
rectangle = new Rectangle(2. , 1.);

System.out.println(square);
System.out.println(dice);
System.out.println(brick);
System.out.println(rectangle);
}
}

5th week doin java

i'm getting used to it..

here's what i got today
selection statement and repetition

selection :
- using if statement
- using switch statement
- write boolean expression
- evaluate given boolean expression correctly
- nested if
- comparing objects
- selecting statement for given task

if syntax
- if ( )

else


relational operator
> more than
< less than
>= more than or equal to
<= less than or equal to
== equal to
!= not equal to

nested if
- if (comparing something){
if (comparing something){
do something
}
}


boolean operator
&& and
|| or
! not

boolean vars
- value : true / false

comparing object
- using ==
ex : String str1 = new String("java");
String str1 = new String("java");
str1 != str2
the location is different
ex : String str1 = new String("java");
str2 = str1
str1 == str2
the location is the same
- another way (to check only the value)
ex : if(str1.equals(str2)){
. . .
}

using switch case
- another branching statement with many possibilities
ex : switch ( N ){
case 1 : x = 30;
break;
case 2 : x = 40;
break;
case 3 : x = 50;
break;
default

trying something new
- using if statement and JOptionPane and also parseInt (converting String to Integer)
- here it is
IdealWeight.java
import javax.swing.JOptionPane;
public class IdealWeight {

public static void main(String[] args) {
int height,age;
double rec;

height = Integer.parseInt(JOptionPane.showInputDialog("input height : "));
age = Integer.parseInt(JOptionPane.showInputDialog("input age : "));

rec = (height - 100 + age / 10) * 0.9;

if(height > 140 && height < 230 && age > 0 && age < 100){
JOptionPane.showMessageDialog (null, "recom weight : " + rec );
}
else
JOptionPane.showMessageDialog (null, "error");
}

}


Repetition / looping
- using while - sentinel (have a certain statement to fulfill)
- using for - count controlled (have fixed times of loop)

commong looping mistakes
- off-by-one error
- make sure there is a statement which will terminate the loop
- make sure it loops just as many times as you wanted

while syntax
- while (statement){
do something
}
- while wont do the "something" unless the statement is fulfilled

do-while syntax
- do {
do something
}
- while(statement);
- do-while will do the "something" at least once before it evaluate the condition

for syntax
- for(starting condition; loop terminated condition; statement looped){
do something
}

a game to try on
not perfect, yet its enough for now

import javax.swing.JOptionPane;
public class HiLo {
private int secret,counter=0,guess;

public HiLo(){

secret = (int)(Math.random()*100);

JOptionPane.showMessageDialog(null, "I have a secret number, try and guess what it is");
while(counter<=6){
guess = Integer.parseInt(JOptionPane.showInputDialog("your guess : "));

if(guess < secret){
JOptionPane.showMessageDialog(null, "to low");
}
else if(guess > secret){
JOptionPane.showMessageDialog(null, "to high");
}
else if(guess == secret){
break;
}

counter++;
}
if(guess == secret){
JOptionPane.showMessageDialog(null, "my number is " + secret + ",you win");
}
else if(guess != secret)
JOptionPane.showMessageDialog(null, "my number is " + secret + ",you lost");
}
public static void main(String[] args) {
HiLo x = new HiLo();

}

}

thats all today...

4th

so sleepy..
hv nothing to else say other than what i got at class...

here it is...

menu:
-argument/parameters
-passing obj to method
-constructor
-info hiding dan visibility modifiers
-local vars


info hiding
-the differences are between public or private
-with public,the info is accesible for other class
-with private it is not
-to access it,we need to use method

method
-syntax
( )
-arg# is the parameters which given the method a value to process
-there can be multiple parameters in a method by adding comma between each parameters

get the return value from method
-example
public double getBalance(){
return balance;
}

constructor
-is a special method thats executed when a new instance of class is created
-generated by compiler automatically when the file compiled

passing obj to method
-using object as a parameter in a method

local variables
-generated within a method,known only to that method
-example
public void swapBalance(Account vice,Account versa){
//tempBalance is a local var
double tempBalance=vice.getBalance();
vice.setBalance(versa.getBalance());
versa.setBalance(tempBalance);

thats all...

goin to sleep...