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Why creating a method better than declaring variable as a field?

int timeDuration = duration * MONTHS_IN_A_YEAR;
My online instructor said I should declare a method of name getTimeDuration() rather than creating a field of the same name. My question is a why creating a method is more preferable. Thanks.

This could fall into a style war. Folks from some camps will always use getters, while others rarely do so. You will find no single 100% agreed upon answer.
Practically, there will be little difference between a using a getter on a private final variable vs direct access. Good runtime environments will inline getters, making for only a slight additional overhead.
There are several reasons to prefer using a getter: If the value which is being retrieved is to be considered a part of an API; if the value obtained by the getter will be different in subclasses; if you want to place a break point or log or otherwise track calls to access the value; if you want a place to attach documentation of the value obtained by the getter, which would be the getter name and explicit documentation.
On the other hand, adding getters does add (a little) code bloat.

One reason, in future if you set variable as private or it will become private data, you are not allowed to access this variable outside the class boundary. So, the value of value of variable fetch by such getters and in object oriented getters are used for this purpose and came into action. Here getters is method like getTimeDuration().

Some code snippets are called "best practice"s, these are told by experienced people and accepted by developers and programmers because of the reasons like:
more readable code
easy to change for future extending or debugging
better performance
help developers to do better configurations
...
the matter we are talking about (using setter and getter for accessing or modifying fields), has one or some of matters that I have mentioned so it is better for developers to use it.
to talk more specific, by setting a field in a method (which that method is called setter) you can check the user input, put some rules for your code and many more features that some frameworks will give to you as a developer.
accessing the value of a field by a method (which is called getter), might add some abilities in some cases, imagine a situation that you want the user to read the field but not be able to change it. this could be done easily this way.

Android Dev: Avoiding Internal Getters/Setters?

I was reading this section in the Android Dev Guide :
here
and I was wondering what is a "Virtual method call" and what does it mean when it says "locally" using a getter/setter? I'm trying to figure out if what they're saying is avoid using methods EVER (for instance a method from an instanced object) or just inside a class you're already working in to get a variable?
To sum it up basically, if I'm in a different class and I want to know the value of a variable in a different class will it be more expensive to do otherclass.getX() than to do otherclass.x? Or is it the same performance if it's not within the current class to do either a method or access a public variable directly?

In that article, they are referring internally accessing private members, and doing so with the field directly rather than calling getX() inside the same class.
It is still recommended (and common) to make members private and provide public accessor methods for external use.
HTH

Using getters and setters is more expensive because first the VM will lookup the method from a virtual method table and then make the call.
For faster access on Android directly accessing member variables reduces the overhead

What the article is basically saying is to avoid the getter/setter patten when you can get away with it. In Java, all methods are Virtual that aren't marked with the private or final modifiers, so they are saying that if your code isn't interface to be implemented by other classes, just access the fields directly. Most likely the reason they point this out is because traditionally, the Java recommendation has been to always use the getter / setter pattern so that your variables can be kept private. However, in Android, you can take a pretty severy performance hit if you add this additional layer of abstraction.
So, in summary. If you're creating an API that other classes will implement, then maybe it's worth it to take the performance hit of getters / setters. But, in your own classes that all interact with each and you're not enforcing a contract, just access the variables directly. External classes accessing your class will also experience the same performance gain by accessing the variable directly, but at some point you need to do a performance-to-maintainability assessment to see if you are comfortable making those variables public or if it's worth it to take the hit and use getter / setter methods

There are MANY, MANY good reason to always use getters (and often use setters) in Java and it's still a great practice to adhere to even when writing code for 'Droid.
While naively there is a higher cost with Dalvik using virtual methods (i.e. getters/setters) rather than instance field access - you can avoid this by using ProGuard to inline these calls at build time!
In such a way you adhere to best practices when coding while avoiding any performance hit.

When using Java classes from Jython, do you bother to use the getters and setters? Should you?

It's well known that Python classes cannot have truly private members. The not-as-obvious implication of this is that Java classes' privates are made public to Jython. (Hide thy nakedness, Java!)
So, when using Jython, and accessing a Java classes' privates that would usually be exposed to other Java classes through getters and setters, do you bother to use those methods? Or do you just access the privates directly?
The more pertinent question would be, should you use the getters and setters? If there are side-effects of the methods, then the answer would undoubtedly be 'yes', but if the methods are just there because someone thought that a putting getters and setters everywhere is The Right Thing to do (IMO it's not, just make the damn thing public), then is there any reason to bother with all of Java's extra ceremony?

Although Jython can make non-public Java members accessible from everywhere, this is a feature that must be enabled explicitly. This alone is reason enough for me to honor the visibility of Java classes, otherwise you are risking works on my machine problems.
More principially, you should use the provided property accessors for classes that are not under your control unless you have a very good reason not to: You never know if future versions of the class will do more than just the bare minimum in their getters/setters.
Jython has the nice feature of hiding the accessor methods of JavaBean properties. Jython converts x.foo += 5 into x.setFoo(x.getFoo() + 5. Because usually the backing field of a property has the same name as the property itself, you may have confused this feature with "Jython makes the backing field accessible" even if it does not. I would definitively use this property-accessed-like-fields syntax of Jython: it makes your code more concise and easier to read.

What are the uses of getter/setters in Java? [duplicate]

This question already has answers here:
Why use getters and setters/accessors?
(37 answers)
Closed 7 years ago.
I have seen member variables given a private modifier and then using getter/setter methods just to set and get the values of the variable (in the name of standardization).
Why not then make the variable public itself (Other than cases like spring framework which depends on getter/setters for IOC etc). It serves the purpose.
In C# I have seen getter/setter with Capitalization of the member variable. Why not make the variable public itself?

In order to get a stable API from the first shot. The Java gurus thought that if later on, you might want to have some extra logic when setting/getting an instance member, you don't want to break existing API by replacing public fields with public methods. This is the main reason in Java.
In the case of C#, public properties are used instead of public fields because of binary interface compatibility. Someone asked a similar question right here, on SO.
So, it's all about encapsulating some logic while still preserving interface for... future proofing.

Even back in 2003 it was known that getter and setter methods are evil.

Because interfaces only allow for specifying methods, not variables. Interfaces are the building stones of API's.
Hence, to access a field through an interface, you need to have the getter and setter.

This is done so you can change the getter or setter implementation in your public API after you release it. Using public fields, you wouldn't be able to check values for validity.

Encapsulation
You also mentioned C# properties. These are really just getters/setters under the hood, but with a more concise syntax.

It's part of encapsulation: abstracting a class's interface (the "getters" and "setters") from its implementation (using an instance variable). While you might decide to implement the behaviour through direct access to an instance variable today, you might want to do it differently tomorrow. Say you need to retrieve the value over the network instead of storing it locally—if you have encapsulated the behaviour, that's a trivial change. If other objects are relying on direct access to an instance variable, though, you're stuck.

The most and foremost use for getters and setters in Java is to annoy the developers. The second most important use is to clutter the code with useless noise. Additionally, it forces you to use a different name for the same thing, depending on where you are (inside or outside the class). Not to forget the added ambiguity (do you call the getter inside the class or do you use the field directly?) Next, they are used to allow access to private data but that's just a minor side effect ;)
In other programming languages, the compiler will generate them for you (unless, of course, you provide your own implementations). In Delphi, for example, you have read and write modifiers for fields (just like private, static or final in Java). The define if you'll have a getter or setter generated for you.
Unlike the Delphi guys, the Java guys wanted everything to be explicit. "If it's not in the source, it's not there". So the only solution was to force people to write all the getters and setters manually. Even worse, people have to use a different name for the same thing.

Getters and setters may very well be the greatest lie ever told. They are considered a sign of good design, while the opposite is true. New programmers should be taught proper encapsulation, not to write dumb data carrier classes that contain nothing but getters and setters.
(The idea that you need getters and setters to future-proof your code if you want to change the implementation later on is an obvious case of YAGNI. But that is really beside the point.)

The most common reason is a poor understanding of encapsulation. When the developer believes that encapsulating stuff really just means getters & setters rather than encapsulating behavour.
The valid reasons for having getters/setters are:
1) You are making a generic¹ object such as JComponent. By using a getter/setter rather than direct access to the variable means that you can do some pre-processing on said variable first (such as validate it is with a set range) or change the underlying implementation (switching from an int to a BigInteger without changing the public API).
2) Your DI framework does not support ctor injection. By having just a setter you can ensure that the variable is only set once.
3) (Ties in with #1) To allow tools to interact with your object. By using such a simple convention then GUI tools can easily get all the settings for a given component. An example of this would be the UI builder in NetBeans.
¹ Of the not-Generic type. Bad word to use I know, please suggest an alternative.

Having a setter allows you
perform validation
to fire a property changed event if the new value is different from the previous value
In the case in question there is no need for getter and setter if the value is simply read or written.

Well,
OOP. ;)
Or to be a little more precise:
Getters and Setters are used to provide a defined interface to a classes
properties. Check the OOP link, it describes the concepts more in detail...
K

You'd need encapsulate those attributes if there are constraints for example or to make general validity checks or post events on changes or whatever. The basic use is hiding the attribute from the "outer world".

Some Java frameworks require them (JavaBeans I think).
-- Edit
Some posters are trying to say this is about encapsulation. It isn't.
Encapsulation is about hiding the implementation details of your object, and exposing only relevant functions.
Providing a get/set that does nothing but set a value does not accomplish this at all, and the only reason for them is:
Perform some additional validation before set/get
Get the variable from somewhere else
Integrate with frameworks (EJB)

There are several reasons:
Some Java APIs rely on them (e.g. Servlet API);
making non-final variable public is considered to be a bad style;
further code support: if sometime in future you`ll need to perform some actions before each access/mutation (get/set) of the variable, you will have less problems with it.
In C# constructions like
public int Age
{
get
{
return (int)(today() - m_BirthDate);
}
}
are are just syntactic sugar.

property idea is core in OOP (Object oriented programming). But problem is that Java introduce them not in core of language (syntax / JVM), but (probably few years later??? historics of Java say better) as convention: pair of consistent getters/setter is property in bean, concept of property is in libraries, not in core.
This generate problem in few libraries, framework. Is single getter a read only property or not? That is the question. I.e.in JPA entities if You want implement classic method (algorithm) beggining with "get" like getCurrentTine() is the best mark by #Transient to disable interpretation like property having value.
In other words, I like very much property concept in C# designed 10 years later and better. BTW C# property has getter/setter too, but sometimes/partially hidden, visible at low level debugging. Free from question "why getter" etc ...
In Java world is interesting to read about Groovy concept of property (hidden getter/setter in different way than C#) http://www.groovy-lang.org/objectorientation.html#_fields_and_properties
EDIT: from real life, every java object has getClass() method, tools from java.beans.BeanInfo package report this as property "class", but this not true. It isn't property (readonly property) in full sense. I imagine properties like C# (with his internal hidden name get_Something1) hasn't conflict with "functional" GetSomething2()

How would you access Object properties from within an object method? [closed]

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Closed 10 years ago.
What is the "purist" or "correct" way to access an object's properties from within an object method that is not a getter/setter method?
I know that from outside of the object you should use a getter/setter, but from within would you just do:
Java:
String property = this.property;
PHP:
$property = $this->property;
or would you do:
Java:
String property = this.getProperty();
PHP:
$property = $this->getProperty();
Forgive me if my Java is a little off, it's been a year since I programmed in Java...
EDIT:
It seems people are assuming I am talking about private or protected variables/properties only. When I learned OO I was taught to use getters/setters for every single property even if it was public (and actually I was told never to make any variable/property public). So, I may be starting off from a false assumption from the get go. It appears that people answering this question are maybe saying that you should have public properties and that those don't need getters and setters, which goes against what I was taught, and what I was talking about, although maybe that needs to be discussed as well. That's probably a good topic for a different question though...

This has religious war potential, but it seems to me that if you're using a getter/setter, you should use it internally as well - using both will lead to maintenance problems down the road (e.g. somebody adds code to a setter that needs to run every time that property is set, and the property is being set internally w/o that setter being called).

Personally, I feel like it's important to remain consistent. If you have getters and setters, use them. The only time I would access a field directly is when the accessor has a lot of overhead. It may feel like you're bloating your code unnecessarily, but it can certainly save a whole lot of headache in the future. The classic example:
Later on, you may desire to change the way that field works. Maybe it should be calculated on-the-fly or maybe you would like to use a different type for the backing store. If you are accessing properties directly, a change like that can break an awful lot of code in one swell foop.

I'm fairly surprised at how unanimous the sentiment is that getters and setters are fine and good. I suggest the incendiary article by Allen Holub "Getters And Setters Are Evil". Granted, the title is for shock value, but the author makes valid points.
Essentially, if you have getters and setters for each and every private field, you are making those fields as good as public. You'd be very hard-pressed to change the type of a private field without ripple effects to every class that calls that getter.
Moreover, from a strictly OO point of view, objects should be responding to messages (methods) that correspond to their (hopefully) single responsibility. The vast majority of getters and setters don't make sense for their constituent objects;Pen.dispenseInkOnto(Surface) makes more sense to me than Pen.getColor().
Getters and setters also encourage users of the class to ask the object for some data, perform a calculation, and then set some other value in the object, better known as procedural programming. You'd be better served to simply tell the object to do what you were going to in the first place; also known as the Information Expert idiom.
Getters and setters, however, are necessary evils at the boundary of layers -- UI, persistence, and so forth. Restricted access to a class's internals, such as C++'s friend keyword, Java's package protected access, .NET's internal access, and the Friend Class Pattern can help you reduce the visibility of getters and setters to only those who need them.

It depends on how the property is used. For example, say you have a student object that has a name property. You could use your Get method to pull the name from the database, if it hasn't been retrieved already. This way you are reducing unnecessary calls to the database.
Now let's say you have a private integer counter in your object that counts the number of times the name has been called. You may want to not use the Get method from inside the object because it would produce an invalid count.

PHP offers a myriad of ways to handle this, including magic methods __get and __set, but I prefer explicit getters and setters. Here's why:
Validation can be placed in setters (and getters for that matter)
Intellisense works with explicit methods
No question whether a property is read only, write only or read-write
Retrieving virtual properties (ie, calculated values) looks the same as regular properties
You can easily set an object property that is never actually defined anywhere, which then goes undocumented

Am I just going overboard here?
Perhaps ;)
Another approach would be to utilize a private/protected method to actually do the getting (caching/db/etc), and a public wrapper for it that increments the count:
PHP:
public function getName() {
$this->incrementNameCalled();
return $this->_getName();
}
protected function _getName() {
return $this->name;
}
and then from within the object itself:
PHP:
$name = $this->_getName();
This way you can still use that first argument for something else (like sending a flag for whether or not to used cached data here perhaps).

I must be missing the point here, why would you use a getter inside an object to access a property of that object?
Taking this to its conclusion the getter should call a getter, which should call a getter.
So I'd say inside an object method access a property directly, especially seeing as calling another method in that object (which will just access the property directly anyway then return it) is just a pointless, wasteful exercise (or have I misunderstood the question).

It is better to use the accessor methods, even within the object. Here are the points that come to my mind immediately:
It should be done in the interest of maintaining consistency with accesses made from outside the object.
In some cases, these accessor methods could be doing more than just accessing the field; they could be doing some additional processing (this is rare though). If this is the case, accessing the field directly would mean that you are missing that additional processing, and your program could go awry if this processing is always to be done during those accesses.

If you mean "most encapsulation" by "purist", then I typically declare all my fields as private and then use "this.field" from within the class itself. For other classes, including subclasses, I access instance state using the getters.

The question doesn't require an opinion based answer. It is a subject well covered by computing science for decades from the principle of high cohesion, low coupling and the SOLID principles.
The purist, read correct, OO way is to minimise coupling and maximise cohesions. Therefore both should be avoided and the Law of Demeter followed by using the Tell Don't Ask approach.
Instead of getting the value of the object's property, which tightly couples the two class, use the object as a parameter e.g.
doSomethingWithProperty() {
doSomethingWith( this.property ) ;
}
Where the property was a native type, e.g. int, use an access method, name it for problem domain not the programming domain.
doSomethingWithProperty( this.daysPerWeek() ) ;
These will allow you to maintain encapsulation and any post-conditions or dependent invariants. You can also use the setter method to maintain any pre-conditions or dependent invariants, however don't fall into the trap of naming them setters, go back to the Hollywood Principle for naming when using the idiom.

i've found using setters/getters made my code easier to read. I also like the control it gives when other classes use the methods and if i change the data the property will store.

Private fields with public or protected properties. Access to the values should go through the properties, and be copied to a local variable if they will be used more than once in a method. If and ONLY if you have the rest of your application so totally tweaked, rocked out, and otherwise optimized to where accessing values by going through their assosciated properties has become a bottleneck (And that will never EVER happen, I guarantee) should you even begin to consider letting anything other than the properties touch their backing variables directly.
.NET developers can use automatic properties to enforce this since you can't even see the backing variables at design time.

It depends. It's more a style issue than anything else, and there is no hard rule.

I can be wrong because I'm autodidact, but I NEVER user public properties in my Java classes, they are always private or protected, so that outside code must access by getters/setters. It's better for maintenance / modification purposes. And for inside class code... If getter method is trivial I use the property directly, but I always use the setter methods because I could easily add code to fire events if I wish.

If I don't edit the property, I'll use a public method get_property() unless it's a special occasion such as a MySQLi object inside another object in which case I'll just make the property public and refer to it as $obj->object_property.
Inside the object it's always $this->property for me.

Well, it seems with C# 3.0 properties' default implementation, the decision is taken for you; you HAVE to set the property using the (possibly private) property setter.
I personally only use the private member-behind when not doing so would cause the object to fall in an less than desirable state, such as when initializing or when caching/lazy loading is involved.

I like the answer by cmcculloh, but it seems like the most correct one is the answer by Greg Hurlman. Use getter/setter all the time if you started using them from the get-go and/or you are used to working with them.
As an aside, I personally find that using getter/setter makes the code easier to read and to debug later on.

As stated in some of the comments: Sometimes you should, sometimes you shouldn't. The great part about private variables is that you are able to see all the places they are used when you change something. If your getter/setter does something you need, use it. If it doesn't matter you decide.
The opposite case could be made that if you use the getter/setter and somebody changes the getter/setter they have to analyze all the places the getter and setter is used internally to see if it messes something up.