03 Language

8/2/2019 03 Language

1/22

Lecture 3:

The J# Language


2/22

2Microsoft

Introducing CS using .NET

J# in Visual Studio .NET 3-2

Objectives

J# brings the Java programming language (1.4) to the .NET platform,providing full access to the .NET Framework

The J# language by way of example


3/22

3Microsoft



Java and J#

Using an example, let's take a tour of J#

Goal?

- to demonstrate that J# can be viewed as pure Java


4/22

4Microsoft



Banking Application

Neighborhood bank needs app to process daily transactions daily transactions reside in a file "transactions.txt"

at night, transactions are applied to customer accounts storedin "customers.txt"

transactions.txt

customers.txt Banking App


5/22

5Microsoft



Program design

Design will consist of 4 classes:

App, Customer, CustomersIO, Transactions

App

main( ) CustomersIO

read(filename) : Customer[ ]write(customers, filename)

Transactions

process(customers, filename)

Customer

represents 1 Customer1

n

1

1


6/22

6Microsoft



Main program

Coordinates transaction processing

1. read customer data into array of Customerobjects

2. process transactions by updating objects

3. write objects back to file when done

public classApp

{

public static voidmain(String[] args)

{

System.out.println("** Banking Application **");

Customer[] customers;

customers = CustomersIO.read("customers.txt");

Transactions.process(customers, "transactions.txt");CustomersIO.write(customers, "customers.txt");

System.out.println("** Done **");

// keep console window open......


7/22

7MicrosoftIntroducing CS using .NETJ# in Visual Studio .NET 3-7

Exception handling

Main program should deal with possibility of exceptions:

public classApp

{


{

try

{


..

.System.out.println("** Done **");

}

catch(Exception ex)

{

System.out.println(">> ERROR: " + ex.toString());

}

finally{ // keep console window open...

System.out.println();

System.out.print("Press ENTER to exit...");

try { System.in.read(); } catch(Exception ex) { }

}}//main

}//class


8/22


Build & run

Stub out the classes & methods,build & run

test normal execution

test throwing ajava.io.IOException


9/22


Customer class

Represents 1 bank customer

minimal implementation at this point

public class Customer

{

public String firstName, lastName; // fields

public int id;

public double balance;

public Customer(String fn, String ln, int id, double balance)

{

this.firstName = fn; // constructor

this.lastName = ln;

this.id = id;

this.balance = balance;

}

public String toString() // method

{

return this.id + ": " + this.lastName + ", " + this.firstName;

}

}

Customer

firstName : StringlastName : Stringid : intbalance : double

Customer(fn, ln, id, balance)toString( ) : String


10/22


CustomersIO class

Reads & writes the customer data

File format:

first line is total # of customers in file

then firstname, lastname, id, balance for each customer

CustomersIO

read(filename) : Customer[ ]write(customers, filename)

7

Jim

Bag

123

500.0

Jane

Doe456

500.0...


11/22


CustomersIO.read( )

First implementread( ), which returns an array of customers

public class CustomersIO

{

public static Customer[] read(String filename) throws java.io.IOException

{

System.out.println(">> reading...");

java.io.FileReader file = new java.io.FileReader(filename);

java.io.BufferedReader reader = new java.io.BufferedReader(file);

Customer[] customers; String fn,ln; int id,N; double balance;

N = Integer.parseInt(reader.readLine());

customers = new Customer[N];

for (int i = 0; i < N; i++)

{

fn = reader.readLine();

ln = reader.readLine();

id = Integer.parseInt(reader.readLine());

balance = Double.parseDouble(reader.readLine());

customers[i] = new Customer(fn, ln, id, balance);

}//for

reader.close();

return customers;

}

"Jane",

"Jim",


12/22


public classApp

{


{

try{


Customer[] customers;

customers = CustomersIO.read("customers.txt");

for (int i = 0; i < customers.length; i++)

System.out.println(customers[i]);

Build & run

Let's test the input code


13/22


CustomersIO.write( )

Now let's implement write( )

public class CustomersIO

{...

public static voidwrite(Customer[] customers, String filename) throws java.io.IOException

{

System.out.println(">> writing...");java.io.FileWriter file = new java.io.FileWriter(filename);

java.io.PrintWriter writer = new java.io.PrintWriter(file);

writer.println(customers.length);

for (int i = 0; i < customers.length; i++)

{

writer.println(customers[i].firstName);

writer.println(customers[i].lastName);writer.println(customers[i].id);

writer.println(customers[i].balance);

}//for

writer.close();

}

"Jane",

"Jim",


14/22


Build & run

To test, just run it twice

first run outputs to "customers.txt"

second run will re-input the new file &check its format


15/22


Transactions class

Reads the bank transactions & updates the customers

File format:

customer id, Deposit or Withdraw, then amount

last transaction is followed by -1

Transactions

process(customers, filename)

123

D

100.0

456

W

100.0

..

.

-1


16/22


Transactions.process( )

Read Tx, find customer, update customer, repeat

public class Transactions

{

public static voidprocess(Customer[] customers, String filename) throws java.io.IOException

{

System.out.println(">> processing...");

java.io.FileReader file = new java.io.FileReader(filename);

java.io.BufferedReader reader = new java.io.BufferedReader(file);

String action; int id; double amount; Customer c;

id= Integer.parseInt(reader.readLine());

while (id != -1) // for each transaction...

{

action = reader.readLine();

amount = Double.parseDouble(reader.readLine());

c = findCustomer(customers, id);

if (action.equals("D"))c.balance += amount; // deposit

else

c.balance -= amount; // withdrawal

id = Integer.parseInt(reader.readLine()); // next Tx please...

}//while

reader.close();

}


17/22


findCustomer( )

Performs a linear search, returning first matching customer

.

.

.private static Customer findCustomer(Customer[] customers, int id)

{

for (int i = 0; i < customers.length; i++) // for each customer...

if (customers[i].id == id)

return customers[i];

// if get here, not found...

return null;

}

}//class

"Jane",

"Jim",


18/22


Build & run

Program should be complete at this point!

but let's check with debugging output

extend Customer to output balance

public class Customer

{...

public String toString()

{

return this.id + ": " + this.lastName

+ ", " + this.firstName

+ ": " + this.getFormattedBalance();

}

public String getFormattedBalance(){

java.text.DecimalFormat formatter;

formatter = new java.text.DecimalFormat("$#,##0.00");

return formatter.format(this.balance);

}

}//class


19/22


J# is Java!

Program we just developed is pure Java

compiles with both Visual Studio .NET and Sun's JDK

transactions.txt

customers.txt Banking App


20/22


Compiling with Java:

If you have Sun's JDK installed, you can compile and run theapp we just built:

rename .jsl files to .java

javac *.java

create sub-directory called BankingApp (since files are part ofthe package BankingApp)

move .class files into BankingApp sub-directory

copy "customers.txt" and "transactions.txt" into currentdirectory (not the BankingApp sub-directory)

java BankingApp/App


21/22


JavaDoc comments

Support for JavaDoc comments provided by Visual Studio .NET

Tools menu, Build Comment Web Pages

@param and @return are supported; others are ignored(@author, @version, and @see)

package BankingApp;

/**

* Main class for Banking Application.

*

* Author: Joe Hummel,

* Date: April 2004

*/

public classApp

{

.

.

.


22/22


Summary

J# is Java on the .NET platform

at least at the level of Java 1.4, with a subset of the classlibraries.

eventually we'll see what else J# can do

Date post:	05-Apr-2018
Category:	Documents
Upload:	nitaxx
View:	216 times
Download:	0 times

03 Language

Documents