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Java Programming: Scanner, Foreach, Interfaces, Classes, Objects, Cohesion, Decoupling, Slides of Computer Engineering and Programming

An introduction to various java programming concepts including using the scanner class for user input, the foreach loop construct, working with interfaces, creating classes and objects, understanding cohesion and decoupling. It includes examples of command-line arguments, handling integers, and creating applets.

Typology: Slides

2011/2012

Uploaded on 07/11/2012

dhananad
dhananad 🇮🇳

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Getting Input Using Scanner
1. Create a Scanner object
Scanner scanner = new Scanner(System.in);
2. Use the methods next(), nextByte(), nextShort(),
nextInt(), nextLong(), nextFloat(), nextDouble(), or
nextBoolean() to obtain to a string, byte, short, int,
long, float, double, or boolean value. For example,
System.out.print("Enter a double value: ");
Scanner scanner = new Scanner(System.in);
double d = scanner.nextDouble();
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Download Java Programming: Scanner, Foreach, Interfaces, Classes, Objects, Cohesion, Decoupling and more Slides Computer Engineering and Programming in PDF only on Docsity!

1

Getting Input Using Scanner

1. Create a Scanner object

Scanner scanner = new Scanner(System.in);

2. Use the methods next(), nextByte(), nextShort(),

nextInt(), nextLong(), nextFloat(), nextDou ble(), or

nextBoolean() to obtain to a string, byte, short, int,

long, float, d ou ble, or boolean valu e. For exam ple,

System.out.print("Enter a double value: "); Scanner scanner = new Scanner(System.in); double d = scanner.nextDouble();

Foreach Loop (new loop construct)

int [] a= new int[5];

foreach(int i in a){

System.out.println(“”+i);

}

2

Program

Development

Example 1 – Command Line Args

/*program displays command-line arguments on

*the screen.

*/

public class Program2 {

public static void main (String[] args) { System.out.println (“Hello ” + args[0]); }// end main

}// end Program2 class

Creating Applets

 Unlike Java Applications, Java Applets run in Java-enabled web browsers such as Netscape, Internet Explorer, Hot Java, etc.

 Basic steps to create an applet:

1. Create a Java source file HelloWorld.java import java.applet.Applet; import java.awt.*; public class HelloWorld extends Applet { public void paint(Graphics g) { // display message g.drawString (“ Welcome to Java ”, 25, 50); }// end paint }// end HelloWorld applet class 2. Create an HTML file to accompany your applet: hello.html A Simple Program Here is the output of my program: <APPLET CODE="HelloWorld.class" WIDTH= HEIGHT=25> Docsity.com

Creating Applets: (Contd.)

  1. Compile the source file

$ javac HelloWorld.java

  1. Run the program $ appletviewer hello.html

Choosing Classes

 A class represents a single concept

  • Concepts from mathematics: Point Rectangle Ellipse
  • Concepts from real life BankAccount Purse
  • Actors StringTokenizer Random (better called RandomNumberGenerator)
  • Utility classes--no objects, only static methods Math

Cohesion

 Cohesive = public interface closely related to the single concept that the class represents

 This class lacks cohesion: public class Purse { public Purse(){...} public void addNickels(int count){...} public void addDimes(int count){...} public void addQuarters(int count){...} public double getTotal(){...}

public static final double NICKEL_VALUE =0.05; public static final double DIME_VALUE =0.1; public static final double QUARTER_VALUE =0.25; ... }

Decoupling

 A class depends on another if it calls

one of its methods

 Purse depends on Coin because it

calls getValue on coins

 Coin does not depend on Purse

 High Coupling = many class

dependencies

 Minimize coupling to minimize the

impact of interface changes

Dependency Relationship between

Purse and Coin Classes