When can I make instance variables public?

I noticed that some of the in-built Java classes have public instance variables, for example in Rectangle the variables x, y, width and height are all directly accessible from outside. When is it okay to make public instance variables? Is it when they are primitive types? I thought maybe it is when they are final variables - but that can't be the case because you can directly modify the Rectangle's public instance variables.
I've always used getter and setter methods in my objects because I was told "making instance variables public is bad". But obviously this isn't necessarily the case (unless the guys at Java are bad programmers). I think directly accessing the instance variables makes for much neater and more readable code. Is there any convention or best-practise guidelines on when I can or can not make them public?
P.S. I also just "don't get" why you can't make them public if you're just going to provide a getter and setter method anyway... what's the difference? I suppose the theory is that the setter method should do some checking to make sure the input is valid. But what if the setter method just accepts -anything- of the appropriate type (accepts any Rectangle, for example)? What's the use of hiding the instance variables?
teach me.
Thanks. ;-)

For the most part, it is true that making instance member variables other than private is not a good idea. This concept, known in OO circles as "information hiding", typically allows the greatest flexibility in internal implementation of a class, since you can change the internal structure of the class without affecting the clients that use the class.
Let me add that Sun's programmers are a team, and teams have members of differing capabilities.
It is also true that there may be cases where exposing instance variables is unlikely to cause problems. Simple classes, or very stable classes that will not change are some examples, but not all.
Following a guideline blindly is not a good idea either. You need to evaluate each instance in which you decide you might want to deviate from "good programming practices". Still, best practices are best practices for a reason. It is best to understand them, and then decide if you can violate them.
For my own part, I don't think it is "neater" to expose such variables, and I have personally had to deal with situations where a change in a class's internal structure was extremely painful because the original developer chose to make all his instance variables public.
{?

Similar Messages

Is there any reason (laziness aside) to declare instance variables public?

Why would you declare one public, save for the fact that object.field is quicker to type than object.getField()? It is a pain to have to write get/set methods for private variables, but later on, if you ever need to do something with a variable when it's been accessed or modified, it's much easier to go back and edit just those methods, instead of everywhere the variable's been directly accessed. On the other hand, I see no benefit of declaring a variable public. Is there one?

Never, Never, Never !!!That's a tad extreme.
In most cases, you'll want get and set, and even then you need to examine whether you really want another class to have that direct control over your object's state.
But there are cases where you can make your instance variables public. If it's a pure data container, with no behavior, and you don't expect it to ever be used in a multithreaded context or to be used as a JavaBean, then you can make the instance variables public.

When can i make a single edition for an android device?

From Amsterdam, Europe
As an Adobe-cloud member......
1:
when can I make a single edition for an android device?
2:
why can I NOT make a single edition for Android ...
Whe are not able to use the single edition at all in Europe...(why actually??)
No one knows when it will be possible....
And then also what about Android, I do not want to use Apple's hardware, but actually I am forced to do so....I think that that is a big minor for Adobe...
regards, Anne

The original problem with android was the file size of the app, i think it was limited to 25/50Mb so have a multi-issue app solved that as the full content was downloaded from adobe servers.
That may still be the issue, though I thought the file size had been increased.
You dont have to use a Mac to create you folio's etc, you just need a mac to upload the binary, not Adobe's fault :-) and everyone is in that boat, so not a big minor for adobe then, just you maybe
have a good weekend
Alistair

Can i use instance variables in page flow controller with out restriction?

I am using instance variable in pageflow controller.
1) Will it give any problem if concurrent users are accessing that controller class?
2) How many controller objects will be created if multiple users (Say 10 users) accessing same controller class?
Thanks.

1) Will it give any problem if concurrent users are accessing that controller class? Pageflows are pere user session, different users wont cause it problems. however a single user can cause problems by using open new tab on a link etc(or back button or refresh on browser, problems with using state in a stateless protocol) . A bigger problem is that since a pageflow is indirect in session, using private variables in pageflow increases your session footprint and in a cluster , if replicated, your network trafiic as well. Using state also causes problem in HTTP , a stateless protocol,. Highly not recommended (unless you have no other choice)
2) How many controller objects will be created if multiple users (Say 10 users) accessing same controller class? 10. assuming the portlet is used once only. If you use the same portlet in multiple pages , then you have that many.
Edited by: deepshet on Feb 27, 2010 12:10 PM

Can anyone tell me why I'm getting this error when trying to make visibility variables

I have set these up in previous versions of Illustrator. CS and illustrator 10 worked just fine with Variables. Now I can't seem to switch between data sets. I just keep getting this error when I try to switch from one data set to another.

I'll start with the permissions and see if it changes the behavior.

How can I make a variable-size list ?

Hi guys,
I'm trying to make a flexible list using <mx:List> component, I mean when I add an item or if the item size is changed (ex: collapse/expand) the list size must change.
Is there an easy way to do that ? If you have any idea, please don't hesitate to post it here. Thanks in advance.
Ygor

It sounds like you're doing 2 distinct things; 1) adding new items to the dataProvider, 2) The item renderer is expanding or collapsing.
If that is the case: 1) when you add an item to the dataProvider, increase the size of the list, 2) when the item renderer is expanding or collapsing, access the list through the "owner" property of the item renderer to change the size of the list.

How can I make a report public so the user doesn't have to login

I am new to apex and am looking at using some of the reporting tools in apex to create reports in our existing application which is all hand coded htp.p calls
The users already login to our application using their own oracle users and passwords through modplsql so I want to be able to embed the apex report into our application without the need to logon.
Thanks
Robert

Thanks, I'm not sure if I'm being a bit thick but I can't see that!
I've gone to
Home>Application Builder>Application 105>Page 1
which is my page deffinition and under security it just tells me 'No authorization schemes defined.'
There is no Authentication option so I guess I'm looking in the wrong place!?

Public instance variable vs. accessor method

I know some OOP purists believe all instance variables should be private, and if there's a need to view or set the value of these instance variable, public accessor methods need to be created. Data encapsulation is the driving force behind this belief.
But in Java, it's easy enough to declare an instance variable public thus eliminating the need to write accessor method. What's the rational behind this feature? Is it merely to save developer some time from typing in the accessor methods? Does this reason justify the use of public members?

I know some OOP purists believe all instance variables
should be private, ALL? No way!
and if there's a need to view or
set the value of these instance variable, public
accessor methods need to be created. There has to be a reason for any :- public int getMyInt(){ ...
and in many cases protected or default package is more appropriate
Data
encapsulation is the driving force behind this belief.
Correct , also avoiding multiple instances of member states - very often its a control issue too
But in Java, it's easy enough to declare an instance
variable public Yes and its also easy enough to write shittie code too ...
if an instance variable is public there should be a clear comment explaining why the field has to be public
thus eliminating the need to write
accessor method. There's nothing wrong with accessors and mutators - the java language is full if them
What's the rational behind this
feature? As you stated encapsulation
Is it merely to save developer some time
from typing in the accessor methods? This is a lame reason
Does this reason
justify the use of public members?and attract unwanted side effects?
I also don't like to see (or to write) a huge long list of getters and setters at the bottom of any class file and find it quite ugly - You should use them when you need to, not as a matter of routine.
Accessor - mutator is a design issue for private instance variables that you wish to keep hidden. Your suggestion to make them all public is also a design issue and if I was to see a long list of public variables at the beginning of a class (unexplained with javadoc comments) I would be very puzzled indeed.
Eclipse will automate the generation of accessors and mutators for you and also has a refactoring tool too - both are extremely useful

Need a little help with instance variables

I'm still pretty new to this, but what I have here is some instance
variables that I need to constuct a record from. This keeps track of a
sorting process. In the public Sortable getRecord() method is where
I need to construct that record, which is where I'm lost.
I look at the tutorials on this site but still can't seem to find what I'm looking for.
What's giving me so much trouble is that I have variables of different types
and I can't out how to group them togther without getting some wierd error.
public class SortableSpy implements Sortable {
    public Sortable a; // Sortable is an interface that this class inplements
    public int swaps;
    public int compares;
    public SortEvent events [];
    public int nevents;
    public SortableSpy(Sortable arr) {
            a = arr;              // These are
            swaps = 0;
            compares = 0; // the variables I need
            nevents = 0;
            events = new SortEvent[1000]; // to use
    public Sortable getRecord() {
         // and this is where I need the record to be constructed
       // then another class will call this record which will keep track
      // of compares and swaps
          return ;
     Thanks for any help anybody can give me

Why do you have a field that's the same type
(implements the same interface) as the class itself?
This is possible, of course, but what are you hoping
to achieve by doing so?The interface was pre set-up by my professer. Here is the interface
public interface Sortable extends Stringable {
    public int size(); // Number of objects to sort
    public boolean inOrder(int i, int j); // are objs i and j in order?
    public void swap(int i, int j); // Swap objects at i and j
    public Stringable getS(int i); // For debugging - make an
                                  // object being sorted stringable
}>
Your code would be easier to read, both for the
person grading your homework and for anyone who wants
to help you here, if you chose variable names that
have meaning. "a" doesn't qualify.What "a" is suppose to be is an object that is sortable. So when I use a sorting
algorithim it will sort "a". This part was also setup by my proffeser.
>
Where do you expect to get all the data that will go
into those fields?I should've put the entire class here before, instead of just the constuctor
here it is:
public class SortableSpy implements Sortable {
    public int t;
    public Sortable a;
    public int swaps;
    public int compares;
    public SortEvent events [];
    public int nevents;
    public SortableSpy(Sortable arr) {
            a = arr;
            swaps = 0;
            compares = 0;
            nevents = 0;
            events = new SortEvent[1000];
    public Sortable getRecord() {
          return a;
     // ** construct a SortRecord from the instance variables
    public String brief() { // or here
            return "Number Of Events" + this.hashCode() + " (" + nevents + ")";
    public String verbose( ) {
          return "Number Of Compares" + this.hashCode() + " (" + compares + ")" +
          "Number Of swaps" + " (" + swaps + ")";
    public boolean inOrder(int i, int j) {
        compares++;
        SortEvent ev = new SortEvent();
        ev.i = i;
        ev.j = j;
        ev.e = EventType.Compare;
        events[nevents] = ev;
        nevents++;
     return a.inOrder(i,j);
    public void swap(int i, int j) {
            int temp = i;
            i = j;
            j = temp;
    public int size() { return nevents;};
    public enum EventType {compare, swap;
     public static Event Compare;}
    private class si implements Stringable {
            private int i;
            public si (int j) { i = j; };
            public String brief() { return " " + i;}
            public String verbose() { return this.brief();}
    public Stringable getS(int i) {
            return a;
}>
getRecord may be better named "createRecord", if I
understand what you're trying to do (I may not). But
it sounds like this name may have been specified by
your professor.
Yeah get record is supose to return the number of times an
algorithm swaps and compares objects during the sorting process
sort of like spying in, as he described
I get the impression that you've misunderstood a
homework assignment.Unfortunaty I'm starting to think so myself, but thanks to both of you guys
for the help you've giving me so far.

What's the difference between global variables and instance variables?

hi im just a biginner,
but what is the difference between these two?
both i declare them above the constructor right.
and both can access by any method in the class but my teacher said
global variables are not permitted in java....
but i don't know what that means....and i got started to confuse these two types,,
im confusing.......
and why my teacher said declaring global variables is not permitted,,,,,,
why.....

instance variables are kindof like Global variables. I'm not surprised you are confused.
The difference is not in how they are declared, but rather in how they are used.
There are two different "styles" of programming
- procedural programming.
- object oriented programming.
Global variables are a term from Procedural programming.
In this style of programming, you have only one class, and one "main" procedure. You only create one instance of the class, and then "run" it.
There is one thread of control, which goes through various methods/procedures to accomplish your task.
In this style of programming instance variables ARE "global" variables. They are accessible to all methods. There is only one instance of the class, and thus only one instance of the variables.
Global variables are "bad" BECAUSE you can change them in any method you like. Even from places that shouldn't have to. Also if you use the same name as a global variable and a local variable, you can cause great trouble. This can lead to very subtle bugs, as the procedures interact in ways you don't expect.
The preferred method in procedural programming is to pass the values as parameters to the methods, and only refer to the parameters, and local variables. This means that you can track exactly what your method is doing, and what it affects. It makes it simpler to understand. If you use global variables in your methods, it becomes harder to understand.
So when are instance variables not global variables?
When you are actually using the class as an Object, rather than just a program to run. If you are creating multiple instances of an object, all with different values for their instance variables, then they are not global variables. For instance you declare a Person object with an attribute "firstname". Your "main" program then creates many instances of the Person object, each with their own "firstname"
I guess at the end of all this, it comes down to definitions.
Certainly you can write procedural code in java. You can treat your instance variables, for all intents and purposes like global variables.
I can only think to show a sort of example
public class Test1
   User[] users;
   public void printUsers(){
     // loop through and print all the users
     // uses a global variable
      for(int i=0; i<users.length; i++){
        users.printUser();
public void printUsers(User[] users){
// preferred method - pass it the info it needs to do the job
for(int i=0; i<users.length; i++){
users[i].printUser();
public Test1(){
User u1 = new User("Tom", 20);
User u2 = new User("Dick", 42);
User u3 = new User("Harry", 69);
users = new User[3];
users[0] = u1;
users[1] = u2;
users[2] = u3;
printUsers();
printUsers(users);
public static void main(String[] args)
new Test1();
class User{
String firstName;
int age;
public User(String name, int age){
this.firstName = name;
this.age = age;
public void printUser(){
// here they are used as instance variables and not global variables
System.out.println(firstName + " Age: " + age);
Shit thats a lot of typing, and I'm not even sure I've explained it any good.
Hope you can make some sense out of this drivel.
Cheers,
evnafets

Inheritance and private instance variables

I've been reading a Java book. It says you should normally make your instance variables private and use getter/setter methods on them, but if you create a superclass, you have to make those variables public (or default?) to inherit them in the subclasses, right? And you can't redefine the variables as private in the subclass, can you?
I'm a little confused on this point. Thanks for any light anyone could shed on this.
=====
Nevermind...I think I figured it out!
Message was edited by:
NovaKane

Thanks to both of you for your responses. I think I've pretty much done what you did, Anan, in this little test program.
public class Animal
   private String name=null;
   public void setName(String n)
      name=n;
   public String getName()
     return name;
   public void makeSound()
public class Dog extends Animal
   public void makeSound()
      if (getName() !=null)
         System.out.println(getName()+" says, \"Bow Wow!\"");
      else
         System.out.println("I don't have a name...but \"Bow Wow!\"");
public class Cat extends Animal
   public void makeSound()
      if (getName() != null)
         System.out.println(getName()+" says, \"Meow!\"");
      else
         System.out.println("I have no name...but, \"Meow!\"");
import java.util.*;
public class Test
   public static void main(String[] vars)
        ArrayList<Animal> animals = new ArrayList<Animal>();
        Animal d = new Dog();
        Animal c = new Cat();
        d.setName("Fido");
        c.setName("Fluffy");
        animals.add(d);
        animals.add(c);
        for (Animal a : animals)
            a.makeSound();
}The "name" instance variable is private, but I can get at it through the getter/setter methods of the superclass, which are public. I should NOT be able to say something like...
d.name="Fido";Right?

How to use an BPM Instance Variable in JSP page

Hi All,
I am using the JSP Presentation, but i don't know how to use an Instance variable in JSP page, that instance already declared in the process. And Can u explain the syntax that to include the JS file into jsp page
Regards
Vasu.
Edited by bpmvasu at 04/03/2007 10:43 PM

Hi Mariano,
I'm using JSP presentation too. In "Interactive Component Call" active i'm using "Use JSP presentation", but i only can define one instance variable, i need to add more instance variables. In "Advanced" option of this task, i have the argument mapping .. but i don't understand how to use it.
I have a instance variable called "genders" of the type String[Int] (Associative Array) and i'm mapping this instance variable in "Arguments Show In" option of the advanced option of JSP presentation. In JSP presentation i have the code:
<select <f:fieldName att="person.gender"/>>
               <c:forEach var="gender" begin="0" items="${genders}" varStatus="status">
                    <c:choose>
                         <c:when test="${person.gender == gender}">
                              <option value="<c:out value="${gender}"/>" selected="true"><c:out value="${gender}"/></option>
                         </c:when>
                         <c:otherwise>
                              <option value="<c:out value="${gender}"/>"><c:out value="${gender}"/></option>
                         </c:otherwise>
                    </c:choose>
               </c:forEach>
          </select>And in my screenflow i have the code:
genders[0] = "Male"
genders[1] = "Female"But when i run my application, i have the error: "The task could not be successfully executed. Reason: 'java.lang.ClassCastException: java.lang.Integer'."
What's the problem?

Binding: Instance variable loses value.

Hi all,
Just making my first steps into Objective-C, I've done a lot of C, C++ and C# on win & linux. Anyhow, I've been hacking away happily and discovered a peculiar behaviour, and I'm not sure if it's my code or some obscure bug in Xcode.
1. I have a Check Box(NSButton) directly bound to a BOOL instance variable called "checkValue" using KVC. The containing class is a custom NSView subclass.
2. I manually implemented the setter according to KVC naming rules "setCheckValue".
3. When debugging the UI (check box) calls the setter perfectly with the correct value, which shows up in the NSLog output.
4. I hooked up the action for the check box as well, and inside the action handler the instance variable reports the value correctly. Everything looks fine.
5. Now here's the rub. I put a mousedown event handler into the class as well, and it is called flawlessly when I click on the custom view. However, "checkValue" does not report the correctly set value.
So, how can a class instance variable, which is set and reports correctly elsewhere in the same scope, all of the sudden take on a nonsense value in a event handler? If a variable has a value set, it should be the same everywhere within the same scope!
Below is simplified code extracted from the original project for clarity. It produces exactly the same behaviour as the more complex project without the distracting code.
#import "CheckBoxHandler.h"
@implementation CheckBoxHandler
@synthesize checkValue;
//Apparently this is required for binding in NSView based classes
//The same behaviour occurs even if you remove this.
+(void)initialize
[self exposeBinding:@"checkValue"];
-(id)initWithFrame:(NSRect)frameRect
self = [super initWithFrame:frameRect];
if(!self)
return nil;
[self setCheckValue:YES];
return self;
//manual impelementation of KVC setter
-(void)setCheckValue:(BOOL)v
checkValue = v;
NSLog(@"Setter Called: checkValue is %d", checkValue);
//The action works fine as evidenced by Log output
//Check and uncheck the box a few times.
-(IBAction)checkBoxAction:(id)sender
NSLog(@"UI State:%d Ivar State: %d", [checkBox state], checkValue);
//Mouse clicking on the view calls into this event.
//The problem is the value reported by [self checkValue] OR checkValue directly
//do not match the UI state. In fact it always reports some nonsense value.
-(void)mouseDown:(NSEvent *)event
NSLog(@"Inside Mousedown: checkValue is: %d", [self checkValue]);
@end
I have a workaround, but it really bends my head when something doesn't behave as expected!

I have synthesized against "checkValue", although I manually implemented the setter so I could set a breakpoint and observe the value. I thought [self checkValue] and self.checkValue both simply call the same getter, just different syntax.
The setting of the value using the UI checkbox happens outside of the event call chain. I can check and uncheck the checkbox and the value changes correctly. The checkbox is in a separate space on the window, so clicking it does not activate mousedown on the view, this is correct behaviour. Clicking on the view does activate the mousedown event, this is done after I've set the checkbox so the value has been set well before the mousedown event. Thus it should already have the correct value in the event.
For completeness this is the interface file:
#import <Cocoa/Cocoa.h>
@interface CheckBoxHandler : NSView {
IBOutlet NSButton *checkBox;
BOOL checkValue;
-(IBAction)checkBoxAction:(id)sender;
@property (assign, readwrite) BOOL checkValue;
@end
I'll change everything to self.checkValue just for the excercise. Ok, done. checkValue still reports a value of 1 in the mousedown event regardless of the value set elsewhere.

Can i make this return a value for papers

class Consumers {
private String firstname;
String Area(){
String Area = "";
if(Area.equalsIgnoreCase("y")) Area = "Urban";
else Area = "Suburban";
return Area;
private String gender;
private static int age;
private String Paper;
private static boolean fashion = false, sports = false,
entertainment = false, healthcare = false;
private static final String Area = "";
/* declare a constructor to initialise */
/* new instances of class Consumers */
public Consumers(String f, String A, String g,
int a, String P) {
firstname = f;
String Area = A;
gender = g;
age = a;
Paper = P;
/* methods to retrieve values of instance variables */
public String getFirstname() {
return firstname;
public String getArea(){
return Area;
public String getGender() {
return gender;
public int getAge() {
return age;
public String getPaper() {
return Paper;
//method to see if paper and consumer are suitable
public boolean isCompatibleTo(String paper2) {
return false;
private static void NewsPaperSupplements() {
// if rules
if(age < 25) {
fashion = true;
if(age < 35){
fashion = true;
sports = true;
if(age < 40){
fashion = true;
if(age < 60){
healthcare = true;
class SundayPapersApplication {
public static void main (String args[]) {
String firstname;
String Area;
Consumers person1;
Consumers person2;
String district;
String gender;
int age;
String Paper = "";
String answer;
// Create a final int variable of 5 customers.
final int numberOfConsumers = 5;
// Stores customers.
Consumers[] allConsumers = new Consumers[numberOfConsumers];
Terminal terminal = new Terminal("");
// Loops and fills with customers.
for(int i = 0; i < numberOfConsumers; i++) {
/* ask user for information about 1st client */
terminal.println("Enter data for 1st person");
firstname = terminal.readString("Firstname: ");
Area = terminal.readString("Area: ");
gender = terminal.readString("Gender (male/female): ");
age = terminal.readInt("Age: ");
/* create a new Client instance with given information */
person1 = new Consumers(firstname, Area,
gender, age, Paper);
/* determine if the given clients are compatible */
terminal.print(person1.getAge() + " " + person1.getArea() + "");
if (person1.isCompatibleTo(Paper))
terminal.println("suitable.");
else
terminal.println("not suitable.");
// Create a new Customer object and store it on the i-th
// place in your array.
allConsumers = new Consumers (firstname, Area,
gender, age, Paper);
for(int i = 5; i < numberOfConsumers; i++) {
// Print customers to the 'terminal'.
out of curosity, now i want to know why it keeps returning void for papers.?
can anyone help again.

it prints out a terminal, which asks the user for the information.
what i was asked to do was return a paper...i.e. fashion / healthcare and entertainment to people under 25 and from an urban area.
the only thing my program does is take the values from the customer and store them to the screen.
i know it's intially set to null....so how do i get the papers applicable to the above age group to print to screen and say whether it is suitable for them. i've tried an IF/Else statement but it doesn't work and im getting even more confused.

Are Instance Variables like Session Vairables?

Hi All!
I am curious to know in what form are the instance variables & attachments getting saved internally. e.g. xml form , cookies etc
Just want to figure out if we use lot many instance variables will it make the session very heavy or are they stored in some kind of xml files.

Actually the instance size limit is configurable. This limit only applies to the 'Normal' instance variables - which are serialized to the Engine's DB as a blob.
If you need to store large amounts of data (more than 16->32kb) you can use Separated instance variables that are serialized differently.
You can always increase the instance size limit, but this will limit the number of concurrent running instances the engine will support.
Attachments are serialized to the engine's DB.
- Tim

When can I make instance variables public?

Similar Messages

Maybe you are looking for