Sunday, September 5, 2010

ET0706 OBJECT ORIENTED PROGRAMMING

Practical 1 useful information:
Note: When creating a new project, it default program look something like this e.g:

public class Practical1 {

}


  • Every Java application must have at least one class, Practical1 is the class name, also known as file name
  • file name is the one you assign to it when you create a java project
  • Java class name and file name must be the same and start with uppercase.

Note2: Each Java application must have the main method in the form of:

public static void main(String args[]){
or public static void main(String[]args)


Note3 : in order to display a single statement we use


System.out.println("Your Message here");


Practical 1 Introduction to Java


Compulsory programming exercises


Q1.1.  Familiarize with IDE. Refer to Lab Guide1
Q1.2.  Write a Java application that display “W” in large block letter which is made up of
           lower case “w”.

Ans:   public class MyFirstJava1 {

       public static void main(String args[]){
              System.out.println("w                 W               w");
              System.out.println("  w              W  W            w");
              System.out.println("    w           W     W        w");
              System.out.println("      w       W         W     w");
              System.out.println("        w   W             W  w");
              System.out.println("          w                 w");
              }
}

Q1.3.  Design a  Java application to display a message box which has the title  "Welcome!" and message "I'm Duke."(hint: refer to Listing 1.3)


Answer:

       import javax.swing.JOptionPane; //declare at the beginning of the java class to use message Dialog box
       public class Practical1 { // class name start with Uppercase

              public static void main(String args[]){ // main method
                     JOptionPane.showMessageDialog(null,"I'm Duke","Welcome", JOptionPane.INFORMATION_MESSAGE);
              //  JOptionPane.showMessageDialog(null,"MessageToBeDisplay","Title",JOptionPane.INFORMATION_MESSAGE);
       System.exit(0); //to release resource, at the end of the java class
        
                     }
       }


Then display “I'm Duke.” using System.out.println() method



Answer:

import javax.swing.JOptionPane;
public class MyFirstJava1 {

       public static void main(String args[]){
              JOptionPane.showMessageDialog(null,"I'm Duke","Welcome", JOptionPane.INFORMATION_MESSAGE);
              System.out.println("i'm Duke!");
              System.exit(0);
              }
}


Practical 2 useful information:
Name variables must always start with lower case e.g int cat;  double car;




Practical 2 Elementary Programming


Compulsory programming exercises

Q2.1 Refer to Lab Guide 2, design a program to get the square of number 11, then
         display it.

Answer:

public class MyFirstJava1 {

       public static void main(String args[]){
              int number1 = 11;
              int displayresult = number1 * number1;
              System.out.println(displayresult);
             
              }
}

         Modify it to get the number from keyboard, then calculate and display the square of the entered number.

Answer:

import javax.swing.JOptionPane;
public class MyFirstJava1 {

       public static void main(String args[]){
             
             
              String strIn = JOptionPane.showInputDialog(null,"Please Enter a Number",   "Display the square of the entered number", JOptionPane.QUESTION_MESSAGE);
             
              int itIn = Integer.parseInt(strIn); //if strIn is “2001”, itIn will be 2001 , convert the string "strIn into integer "itIn"
              /* float fltIn = Float.parseFloat(strIn);*/  //for float
              /*double dblIn = Double.parseDouble(strIn);*/ // for double

              int result = itIn * itIn;

              System.out.println(result);
             
              }
}




Q2.2 Write a program to the prompt the user to enter a voltage and a resistance for a resistor. Calculate and display the current. Note: current = voltage / resistance.


Answer:

import javax.swing.JOptionPane;
public class MyFirstJava1 {

       public static void main(String args[]){
             
             
              String strIn = JOptionPane.showInputDialog(null,"Please Enter the voltage",   "Display the current", JOptionPane.QUESTION_MESSAGE);
              String strIn2 = JOptionPane.showInputDialog(null,"Please Enter the resistance",   "Display the current", JOptionPane.QUESTION_MESSAGE);
              int itIn = Integer.parseInt(strIn);
              int itIn2 = Integer.parseInt(strIn2);//if strIn is “2001”, itIn will be 2001 , convert the string "strIn into integer "itIn"
              /* float fltIn = Float.parseFloat(strIn);*/  //for float
              /*double dblIn = Double.parseDouble(strIn);*/ // for double

              int result = itIn / itIn2;

              System.out.println("Current = voltage / Resistance = " + result);
             
              }
}


Q2.3 Write a program that converts Fahrenheit to Celsius.  
         The formula for the conversion is as follows:
            celsius = (5/9) * (fahrenheit - 32)

         Your program reads a Fahrenheit degree in double from the input dialog box, then
         converts it to Celsius and displays the result in a message dialog box.

         Hint: In Java, 5/9 is 0, so you need to use 5.0/9 in the program to obtain the correct result.
       

 

 

Bonus programming exercises


Q2.4 Write a program that prints a face, hopefully better looking than this one:
     / / / / /
   |  Q   Q |
 {|     /\     |}
   |   \__/   |
   \--------/     Use comments to indicate when you print the hair, ear, mouth, and so on. Hint: to print out “\”, use “\\”

Q2.5 Write a program that reads the subtotal and the gratuity rate, and computes the gratuity and total. gratuity = subtotal * gratuity rate /100, total = subtotal + gratuity. e.g. if the user enters 10 for subtotal and 15 (percent) for gratuity rate, the program displays 1.5 as gratuity and $11.5 as total.

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