OOD Class stuff by AhmadTaiff Isahak

Demo Abstract

taiffdisted — 2017-08-25 03:06:46 UTC

/* package whatever; // don't place package name! */

import java.util.*;
import java.lang.*;
import java.io.*;

/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
public static void main (String[] args) throws java.lang.Exception
{
Student s=new Student();
s.sayHi();
// Person p=new Person();
// p.sayHi();
Person p;
p=s;
p.sayHi();

}
}

abstract class Person {
abstract void sayHi();
/* {
System.out.println("Ahoi from a Person");
}
*/
}

class Student extends Person {
void sayHi() {
System.out.println("Olla from a Student");
}

}

Demo Exception

taiffdisted — 2017-09-06 06:45:54 UTC

Demo Exception with Nested Calls

taiffdisted — 2017-09-06 06:59:11 UTC

import java.lang.Math; // headers MUST be above the first class
import java.lang.Exception.*;

// one class needs to have a main() method
public class HelloWorld
{
// arguments are passed using the text field below this editor
public static void main(String[] args) {
OtherClass myObject = new OtherClass("Hello World!");
System.out.println(myObject);
try {
String s1=myObject.getString("WooHOO");
int i=myObject.getJunk1(); //myObject.getNumber();
String s2=myObject.getString("WhatLaoEh");
}
catch(ArithmeticException e1) {
System.out.println("Yo dude! Go back to Arihtmetic class!");
}
finally {
System.out.println("Finally I'm DONE!");
}
}
}

// you can add other public classes to this editor in any order
public class OtherClass {
private String message;
private boolean answer = false;
public OtherClass(String input) {
message = "Why, " + input + " Isn't this something?";
}
public String toString() {
return message;
}
public int getNumber() {// throws Exception {
int i=3/0;
System.out.println("in GET NUMBER");
return i;
}
public String getString(String stuff) {
System.out.println(stuff);
return stuff;
}
public int getJunk1() {
int a=0;
try {
a=this.getJunk2();
System.out.println("Normal Junk1");
}
catch(ArithmeticException e2) {
System.out.println("Caught ArithmeticException in getJunk1");
}
finally {
System.out.println("in JUNK1");
}
return a;
}

public int getJunk2() {
int b=0;
try {
b=this.getJunk3();
System.out.println("Normal Junk2");
}
finally {
System.out.println("in JUNK2");
}
return b;
}

public int getJunk3() {
int x=10/0;
System.out.println("Normal Junk3");
return x;
}
}

What happens when you click the 'PressMe' button:

taiffdisted — 2017-09-29 02:28:37 UTC

1. Since the Controller is a Listener to the button, the actionPerformed method is called;
2. The actionPerformed method calls the incrementValue() method in the Model;
3. The Model updates the counter value by 1, calls setChanged(), and finally notifyObservers() and passing the new counter value as parameter;
4. Since the View is an Observer (linked to the Model in the RunMVC constructor), it's update() method is called (via notifyObservers());
5. The update() method gets the counter value and sets the textField to the value.

Model.java

taiffdisted — 2017-10-02 02:48:02 UTC

public void decrementValue() {
--counter;
System.out.println("Model : counter = " + counter);
setChanged();
notifyObservers(counter);
}

Controller.java

taiffdisted — 2017-10-02 02:48:36 UTC

public void actionBtnDecrease() {
System.out.println("Controller: acting on Model");
model.decrementValue();
}

public void actionBtnReset() {
System.out.println("Controller: acting on Model");
model.setValue(0);
}

View.java

taiffdisted — 2017-10-02 02:48:59 UTC

...
private Button btnIncrease;
private Button btnDecrease;
private Button btnReset;
private Controller myController;
...

in Constructor:
btnIncrease = new Button("Increase");
btnDecrease = new Button("Decrease");
btnReset = new Button("Reset");
panel.add(btnDecrease);
panel.add(btnReset);
panel.add(btnIncrease);
...
public void addController(ActionListener controller){
System.out.println("View : adding controller");
btnIncrease.addActionListener(controller); //need instance of controller before can add it as a listener
this.myController=(Controller)controller;
btnDecrease.addActionListener(
new java.awt.event.ActionListener() {
public void actionPerformed (java.awt.event.ActionEvent e) {
myController.actionBtnDecrease();
}
}
);
btnReset.addActionListener(
new java.awt.event.ActionListener() {
public void actionPerformed (java.awt.event.ActionEvent e) {
myController.actionBtnReset();
}
}
);

} //addController()

Sample

taiffdisted — 2017-10-06 03:14:37 UTC

SELECT * FROM AYAM WHERE WEIGHT<5

SELECT * FROM AYAM WHERE WEIGHT<5 OR TRUE

String sql="SELECT * FROM AYAM WHERE WEIGHT";

condition="<5 OR TRUE";

String sqlToExec = sql+condition;

Sample

taiffdisted — 2017-10-06 03:16:07 UTC

Table: Balance
acctNo balance
111 1000
222 1000

What SQL statement to execute to transfer 500 from account 111 to 222?

1. SQL1: UPDATE Balance SET balance=500 WHERE accountNum=111
2. SQL2: UPDATE Balance SET balance=1500 WHERE accountNum=222

What happens if system fails after executing SQL1 but before executing SQL2?

acctNo balance
111 500
222 1000

I.e. acctNo has lost 500 to the 'system'!!!

To Avoid, use Transactions
transaction Start
SQL1
SQL2
...
transaction commit

Simple Pause console function

taiffdisted — 2017-10-16 09:23:22 UTC

void pause() {
try {
out.printf("\n\n Press ENTER..");
System.in.read();
}
catch(IOException exe){
out.printf("Error?");
}
}