question about an airline reservation system

> what does this statement means?

>

> seats[ smoking++ ] = 1;

What do you think it means?

prometheuzza at 2007-7-28 18:47:17 >

my question is why do we use these kind of statements? like to increment makes sense by why using an assignment statement?

seats[smoking++] = 1; i know what smoking++ does inside the array but why do we use an assignment statement = 1? that is where i am confused.

if i dont use any assignment statement and do this seats[smoking++] compiler gives me an error which is genuine

schumachera at 2007-7-28 18:47:17 >

> my question is why do we use these kind of

> statements? like to increment makes sense by why

> using an assignment statement?

> seats[smoking++] = 1; i know what smoking++ does

> inside the array but why do we use an assignment

> statement = 1? that is where i am confused.

>

> if i dont use any assignment statement and do this

> seats[smoking++] compiler gives me an error which is

> genuine

I don't understand you.

prometheuzza at 2007-7-28 18:47:17 >

now i understand . so if i assign another alue array[index++] = 777 it will increment the index and place the value at the appropriate index. Thanks

schumachera at 2007-7-28 18:47:17 >

> now i understand . so if i assign another alue

> array[index++] = 777 it will increment the index and

> place the value at the appropriate index. Thanks

that depends on what the appropriate index is...

jwentinga at 2007-7-28 18:47:17 >

By the way, next time please give a little more thought to your subject line. Your question really had nothing to do with and airline reservation system. It was about the post-increment operator.

jverda at 2007-7-28 18:47:17 >

Right, it's called abstraction. If you have an array of ints for seats, you aren't being very object-oriented.

Maybe you can have a Seat class with a variable that indicates whether or not it's been filled:

public class Seat

{

private boolean reserved;

public boolean isReserved() { return reserved; }

public void setReserved(boolean reserved) { this.reserved = reserved; }

}

Now you can iterate through a List of Seats and ask each one if it's been reserved. Nice, self-documenting abstraction.

It's a common mistake for people who don't understand objects to program in too low a level. Everything's a primitive; the most sophisticated data structure is an array.

%

duffymoa at 2007-7-28 18:47:17 >

> > Maybe you can have a Seat class with a variable

> that

> > indicates whether or not it's been filled:

>

> I might even go with a two-valued enum: RESERVED,

> AVAILABLE.

Could be worth doing if a seat can be unreserved and still unavailable.In that case I might add another state to my enum.

>

> * It avoids confusion as to whether true means "yes,

> it's reserved" or "yes it's available". (Though

> always calling reserved() and naming your locals that

> use it reserved will alleviate that too.)

Yes, agreed. That's what I didn't like about 0 and 1. What do those mean?

>

> * If we later find we need another state, we simply

> add it to the enum an add the appropriate handling

> elsewhere. No need to change the type of everything

> that depends on it.

I like it, Jeff.

%

duffymoa at 2007-7-28 18:47:22 >

> It's a bit of a toss-up. An enum might be

> overengineering here--a case of small boy with new

> language feature. I'm mainly just tossing it out

> there as an option, along with a couple of potential

> reasons why it might make sense. It's up to the OP to

> determine if any of that applies to him, or if a

> simple "reserved" boolean is sufficient.

>

> If nothing else, I hope we've planted the seeds of

> examining pros and cons of different approaches

"Ok, so how do I determine if it applies to me?" :)

georgemca at 2007-7-28 18:47:22 >

thanks for the prompt replies. well i was studying core java from deitel. I prefer to use arraylist and list or other data structures. I am lacking in array alot. i dont know why. I've read 2 books already and i am good in programming but bad when anyone ask me to write a program using array. I can do the same thing with an arraylist or list.

So i started reading more books and more assignments on arrays. until i found this code example which is like this

import javax.swing.*;

import java.awt.*;

import java.awt.event.*;

public class PlaneExample extends JApplet

implements ActionListener {

JTextField input;

JLabel prompt1, prompt2;

JButton yesButton, noButton;

int section, seats[], smoking;

int nonsmoking, people;

public void init()

{

input = new JTextField( 4 );

input.addActionListener( this );

prompt1 = new JLabel( "Please type 1 for smoking" );

prompt2 = new JLabel( "Please type 2 for nonsmoking" );

yesButton = new JButton( "Yes" );

noButton = new JButton( "No" );

yesButton.addActionListener( this );

noButton.addActionListener( this );

// The enabled method has not been introduced up

// to this point in the book. It is used here to

// disable the buttons by "graying" them.

yesButton.setEnabled( false );

noButton.setEnabled( false );

seats = new int[ 11 ];

smoking = 6;

nonsmoking = 1;

Container c = getContentPane();

c.setLayout( new FlowLayout() );

c.add( prompt1 );

c.add( prompt2 );

c.add( input );

c.add( yesButton );

c.add( noButton );

}

public void actionPerformed( ActionEvent e )

{

if ( e.getSource() == input && people <= 10 ) {

section = Integer.parseInt( input.getText() );

String s = "";

if ( section == 1 ) {

if ( smoking <= 10 ) {

s = "Smoking. Seat #" + smoking;

seats[ smoking++ ] = 1; //this is where i dont know what was going on

people++;

}

else if ( smoking > 10 && nonsmoking <= 5 ) {

// enable buttons

yesButton.setEnabled( true );

noButton.setEnabled( true );

s = "Smoking is full. Non-smoking?";

}

else

s = "Next flight leaves in 3 hours.";

}

else if ( section == 2 ) {

if ( seats[ nonsmoking ] == 0 && nonsmoking <= 5 ) {

s = "Nonsmoking. Seat #" + nonsmoking;

seats[ nonsmoking++ ] = 1; // same here

people++;

}

else if ( nonsmoking > 5 && smoking <= 10 ) {

// enable buttons

yesButton.setEnabled( true );

noButton.setEnabled( true );

s = "Nonsmoking is full. Smoking?";

}

else

s = "Next flight leaves in 3 hours.";

}

else

s = "Invalid input.";

showStatus( s );

}

else if ( e.getSource() == yesButton ) {

if ( section == 1 ) {

showStatus( "Your seat assignment is " + nonsmoking );

seats[ nonsmoking++ ] = 1;

}

else { // section is 2

showStatus( "Your seat assignment is " + smoking );

seats[ smoking++ ] = 1;

}

people++;

noButton.setEnabled( false );

yesButton.setEnabled( false );

}

else if ( e.getSource() == noButton ) {

showStatus( "Next flight leaves in 3 hours." );

noButton.setEnabled( false );

yesButton.setEnabled( false );

}

}

}

seats[ nonsmoking++ ] = 1;

seats[smoking++ ] = 1;

these were the 2 part which i cannot understand may be because of my lack of practice in arrays.

schumachera at 2007-7-28 18:47:22 >

pardon?

schumachera at 2007-7-28 18:47:22 >

no thanks i got it now.

schumachera at 2007-7-28 18:47:22 >