This question already has answers here:
Why use getters and setters/accessors?
(37 answers)
Closed 6 years ago.
I saw a code where getters and setters methods are declared private. I am trying to figure out the logic behind it, and I am really having hard time to understand why would you declare them as private? That's exactly opposite of what we are trying to achieve through getters and setters.
I can think of several reasons:
you want to prevent future public access.
If a different programmer sees your code and wants access to a variable, but there are no setters and getters, he might think you just forgot about them, and add them themselves. However, if you declare them as private, it's a statement of intent, saying I don't want these variables to be changed or accessed from the outside.
you want to associate setting and getting with other actions
Say you don't want public accessors. But maybe you want a count of how many times a private variable is changed. It's easier to use a setter rather than incrementing the count every time you access that variable.
you want a central access point
Again, you don't want public access, but during debugging, you might want to put a breakpoint in every place a private member is changed. So instead of setting breakpoints everywhere in the class, you just set one in the accessor.
That's exactly opposite of what we are trying to achieve through getters and setters.
Actually, it is not. The reason for declaring public getters and setters is to hide the fields. This is done to avoid unwanted coupling; i.e. clients of an API depending on the implementation details of the API. (That coupling can be problematic for a number of reasons. For example, dependencies on the types of the fields, the possibility of unexpected changes to the fields.)
The reason for declaring the getters and setters private is to make the corresponding part of the object's abstract state (i.e. the values) private. That's largely independent of the decision to use getters and setters or not to hide the implementation types, prevent direct access, etc.
While the case for using getters and setters is not as strong for private state, there are still tangible benefits in using private getters and/or setters. For instance:
The private getter/setter methods provide a place for adding extra behavior or error checking code.
They can provide a place for logging state changes or access to the fields.
They can provide a place for adding your debug code while testing. (Probably not the best way of debugging.)
Related
This question already has answers here:
Why use getters and setters/accessors?
(37 answers)
Closed 5 years ago.
Why do the data members of POJO classes are private and the getter/setter function are public?
Can someone please give solution for this.
Common approach: access to variables by using getters/setters:
better maintainability
accessibility to private properties only for the defining class (isolation)
used for a different data representation (you might have private data to store the birthdate, but create a getter named getAge()).
It doesn't have to be that way, it's just a pattern and it exists for a reason.
All members of a class should be private by default, so that noone can mess up things from outside or read/write values which are not important by the outside. Additionally some internal stuff can change within your class, and the outside world should not care about it.
To allow access from the 'outside world', be it reading or writing anything should be handled via getters/setters/issers to allow a governed manipulation.
Think of it like a mini API of your class - an interface to your class anyone outside can understand and rely on.
If you want to add any validation or modify any other thing before/after setting value of an object, you can use that validation in setter method. Same applies for getter.
It the basic object-oriented principle i.e only object can communicate through message which is called encapsulation.So indirectly you are not exposing your state to outside.For an example class with one attribute age is there and age can not be negative so in setter you can put a check so your object state will not in bad condition.If you access directly the variable then there is no scope for validation.
The basic principle of the oriented object programming is to encapsulate the members of a class and give access to them only via getters and setters
This question already has answers here:
Why use getters and setters/accessors?
(37 answers)
Closed 8 years ago.
I had been asked the following question in an interview and i am curious to know the answer.
There are two classes as following,
public class EmployeeA{
public int empId;
}
public class EmployeeB{
private int empId;
public void setEmpId(int empId){this.empId = empId;}
public int getEmpId(){return empId;}
}
There are two classes where one class has a public instance field and other have a private field with getters and setters. In this case, which is better implementation and why?
[I have learned that making instance variable private is the better idea. But in both cases i can modify the value of empId attribute. ]
The one-word answer they're probably looking for is "encapsulation".
By encapsulating the private field value, you have the opportunity to change the logic on how the value is set/retrieved in the future. Say, for example, you want to validate on set and filter on retrieval (get). By encapsulating the value, your creating an API which allows for better maintenance moving forward.
Maybe a bit off-topic, although people usually talk about "encapsulation" when talking about "getter/setter", "getter/setters" are actually still far from proper encapsulation.
This famous "why getter and setter methods are evil" is something worth to read. When we say getters and setters are evil, it doesn't mean that we should expose variable directly. It is about further hiding internal data by providing meaningful behavior in class, instead of providing accessors for properties. Although there are a lot of cases we still need accessors, this is something that worth giving attention when you are designing.
Going back to your question, if it is me, I will answer: providing getters and setters provides a minimal level of encapsulation and allow us to do extra work or derives data when we are setting and getting properties. However, for a proper encapsulation, I would rather design the Employee class to provide proper behaviors, instead of simply acting as a value object which only provides bunch of getters/setters.
The accesssor (getter) and mutator (setter) are JavaBean requirement but not all classes in Java must follow this design pattern. Why not creating this class as immutable by having a constructor that take the id (or even better, a static factory). You can then provide an accessor for the the id. That is generally not a good idea to be able to change the id of an object, if the id is used in a Map as the key and you change it, good luck to retrieve you object... Make the class immutable solve this kind of problem.
This question already has answers here:
Why Not Use Public Member Functions
(3 answers)
Closed 9 years ago.
I have question which has been going around in my mind since long.
My Model class should have properties private or public? (Below code is written in PHP but question applies in general for any language)
class Xyz extends Model {
public function __call() {
}
public $description;
public $title;
}
In above example I have public properties $description and $title. Should I make them private?
I update my model as follows
$x = new Xyz();
$x->title('Hello');
$x->description('Blah blah');
$x->save();
I can update and get them by using magic method __call. So why do we need to keep them public? I can make them private. But as I see all the frameworks around keep model properties public.
Any thoughts?
UPDATE:
In answers, everyone is saying follow encapsulation and use private methods. Good but no one has the answer why some PHP frameworks have model properties public ? There should be some reason, isn't it?
As per OOP, we need to follow encapsulation. Please make your properties private and have public accessors and mutators. but, it depends that your accessors and mutators can have other modifiers as well. But, The properties should be always private.
Class fields should always be private. Getters and setters for the fields should be public. Aside from being standard, it is also good to have it this way so that you have the control to do what ever you want to the values that the client classes wants to set to you private fields.
For example, if you want to persist an object to a database, and one column is stated to be not null, and you are not sure if your client class will really return a non-null value, you can handle the null check inside the setter so that the values that you are about to persist to the db contains no null field, as what the table of your db demands.
The fields should always be private as per OOP encapsulation principle. Now the thing is with the getter and setter accessor methods.
The getter is usually safe to make it public. The only downside of it is that you will have to maintain backward compatibility between versions, as this will be part of the public contract of the class. So if the field is something that is part of the implementation rather than interface, than maybe you want to keep it protected.
As for the setter the better question is if to create one or not. If you want to keep your class immutable (or at least some parts of it) with all the advantages and disadvantages that comes from it, then you'll not be creating a setter at all.
You have to make all properties as private in model class and if you have to encapsulate their value then you have to use appropriate getters and setters to get and set their values.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Why use getters and setters?
This is a newbie question. Is it very much necessary to use getmethods to access property values? Once the value has been assigned, one can get the values directory. For example, in the below code, displayName() can display firstName value without the help of any getter method. Or it is a standard coding standards that one must have getter and setter method or any other methods which gives that value?
class Test{
private String firstName;
public void setName(String fname){
firstName = fname;
}
public void displayName() {
System.out.println("Your name is " + firstName);
}
}
Tell, Don't Ask is an important principle in object-oriented design. Generally you should tell objects to do things rather than ask them questions. getters/setters every where discourage this practise because you are encouraged to reach inside an object and get to the fields (or even worse reach in and poke things about in the case of setters). This breaks encapsulation and makes your code harder to reason about.
In your particular case, I'd create an object called Name that has a constructor taking the name and single method to display it.
In Your case (to display the display name) it is not neccessary to provide Getter.
But if your want use the field in another class We need to provide the Getter method.
Getter and setters are a part of the standard interface for Java Beans and many frameworks like Hibernate expect them in place. That being said it is of course up to you to decide if and when you need them and for what purpose. They provide access to your private member variables and they can even give you the chance to do more than just plain get and set.
The point of OO software is reuse. This means that other programmers, or you years from now, can use the code for other systems.
When you have private member variables, and use get/set functions, you can change the internal implementation of the function without breaking all the other code that uses it.
Do always use Getter and Setter to access your properties!
You should take a look at this article...
Having private state, encapsulation is good, and in A LOT of cases this is the right thing. Suppose that your class is suppose to be Thread Safe, having public fields you can't ensure that.
On the other hand there are cases when this is useless! Suppose that you access your object only in one package, you are sure you will never export it, then why bother?
I do not have any links to support this, but it's what I do.
I try to avoid public fields if they are not static. So I just use protected and private fields. From within the class, you can access them without get/set, that's completely fine. From outside the class, always try to use get/set.
So your example code is completely fine to me. :)
EDIT: One exception for me is if I create a struct-like container class like this
class Point4D {
public int x1, x2, x3, x4;
}
Then I think that public fields are ok. It would be still better to make them private and name the getters public int x1() etc though. As soon as some methods are introduced to this container that change the state of the instance (like changing the values of x1/x2/x3/x4), I make them private and add get/set.
This question already has answers here:
Closed 10 years ago.
Possible Duplicate:
Why use getters and setters?
I have read books on Java, saying that it is good to create setters and getters for variables such as x and y. For example:
public int getX(){
return x;
}
public void setX(int x){
this.x = x;
}
But what is the difference from that and
...(shape.x)... // Basically getX()
and
shape.x = 90; // Basically setX()
If setters and getters are better, what practical problems would arise?
Multiple reasons:
If you allow field access like
shape.x = 90
then you cannot add any logic in future to validate the data.
say if x cannot be less than 100 you cannot do it, however if you had setters like
public void setShapeValue(int shapeValue){
if(shapeValue < 100){
//do something here like throw exception.
}
}
You cannot add something like copy on write logic (see CopyOnWriteArrayList)
Another reason is for accessing fields outside your class you will have to mark them public, protected or default, and thus you loose control. When data is very much internal to the class breaking Encapsulation and in general OOPS methodology.
Though for constants like
public final String SOMETHING = "SOMETHING";
you will allow field access as they cannot be changed, for instance variable you will place them with getters, setters.
Another scenario is when you want your Class to be immutable, if you allow field access then you are breaking the immutability of your class since values can be changed. But if you carefully design your class with getters and no setters you keep the immutability intact.
Though in such cases you have to be careful in getter method to ensure you don't give out reference of objects(in case your class have object as instances).
We can use the private variables in any package using getters and setters.
Using getter and setter functions allow for constraints and encapsulation. Lets say x is the radius. shape.x = -10 would not make much sense. Also, if someone tries to set an illegal value, you can print an error, set a default value, or do nothing.
It is good practice to make member variables private so they cannot be modified directly by programs using them.
Mutator functions
Encapsulation
A lot of people have mentioned encapsulating the specifics of the implementation, which to me is the biggest reason to use getters and setters in a class. With this, you also get a lot of other benefits, including the ability to throw out and replace the implementation on a whim without needing to touch every piece of code that uses your class. In a small project, that's not a big benefit, but if your code ends up as a well-used (internal or public) library, it can be a huge benefit.
One specific example: complex numbers in mathematics. Some languages have them as a language or framework feature, others don't. I will use a mutable class as an example here, but it could just as easily be immutable.
A complex number can be written on the form a + bi with real and imaginary parts, lending itself well to [gs]etRealPart and [gs]etImaginaryPart.
However, in some cases it's easier to reason about complex numbers on polar form re^(iθ), giving [gs]etRadius (r) and [gs]etAngle (θ).
You can also expose methods like [gs]etComplexNumber(realPart, imaginaryPart) and [gs]etComplexNumber(radius, angle). Depending on the argument types these may or may not need different names, but then the class' consumer can use either as fits its needs.
The two forms are interchangeable; you can fairly easily convert from one to the other, so which form the class uses for internal storage is irrelevant to consumers of that class. However, consumers may use either form. If you choose the form a+bi for internal representation, and expose that using fields rather than getters and setters, not only do you force the class consumers to use that form, you also cannot later easily change your mind and replace the internal representation with re^(iθ) because that turns out to be easier to implement in your particular scenario. You're stuck with the public API you have defined, which mandates that specifically the real and imaginary parts are exposed using specific field names.
One of the best reasons I can think of for getters and setters is the permanence of a class's API. In languages like python you can access members by their name and switch them to methods later. Because functions behave differently than members in java once you access a property thats it. Restricting its scope later breaks the client.
By providing getters and setters a programmer has the flexibility to modify members and behavior freely as long as the adhere to the contract described by the public API.
Another good reason to user getter and setter can be understand by the following example
public class TestGetterSetter{
private String name ;
public void setName(String name){
this.name = name ;
}
public String getName(){
return this.name ;
}
}
The point of getters and setters is that only they are meant to be used to access the private variable, which they are getting or setting. This way you provide encapsulation and it will be much easier to refactor or modify your code later.
Imagine you use name instead of its getter. Then if you want to add something like a default (say the default name is 'Guest' if it wasn't set before), then you'll have to modify both the getter and the sayName function.
public class TestGetterSetter{
private String name ;
public void setName(String name){
this.name = name ;
}
public String getName(){
if (this.name == null ){
setName("Guest");
}
return this.name ;
}
}
There is no requirement for getters and setter to start with get and set - they are just normal member functions. However it's a convention to do that. (especially if you use Java Beans)
Let's say, hypothetically, you find a library that does a better job of what you have been doing in your own class (YourClass). The natural thing to do at this point is to make YourClass a wrapper interface to that library. It still has a concept of "X" which your client code needs to get or set. Naturally, at this point you pretty much have to write the accessor functions.
If you neglected to use accessor functions and let your client code access YourClass.x directly, you would now have to rewrite all of your client code that ever touched YourClass.x. But if you were using YourClass.getX() and YourClass.setX() from the beginning, you will only need to rewrite YourClass.
One of the key concepts of programming, and especially object oriented programming, is hiding implementation details so that they're not used directly by code in other classes or modules. This way, if you ever change the implementation details (as in the example above), the client code doesn't know the difference and doesn't have to be modified. For all your client code knows, "x" might be a variable, or it might be a value that is calculated on the fly.
This is an oversimplification and doesn't cover all the scenarios where hiding implementation is beneficial, but it is the most obvious example. The concept of hiding implementation details is pretty strongly tied to OOP now, but you can find discussions of it going back decades before OOP was dreamed up. It goes back to one of the core concepts of software development, which is to take a big nebulous problem, and divide it into small well-defined problems which can be solved easily. Accessor functions help keep your small sub-tasks separate and well-defined: The less your classes know about each other's internals, the better.
There are lots of reasons. Here are just a few.
Accessors, getters in particular, often appear in interfaces. You can't stipulate a member variable in an interface.
Once you expose this member variable, you can't change your mind about how it's implemented. For example, if you see a need later to switch to a pattern like aggregation, where you want the "x" property to actually come from some nested object, you end up having to copy that value and try to keep it in sync. Not good.
Most of the time you are much better off not exposing the setter. You can't do that with public fields like x.
Before get into the answer, we gotta know something prior...! "JavaBeans".
JavaBeans are java classes that have properties. For our purpose, think of properties as private instance variables. since they're private, the only way they can be accessed
from outside of their class is through 'methods'in the class.
The methods that change a propertiy's value are called setter methods, and the methods that retrieve a property's value are called getter methods.
I would say that neither the getters/setters nor the public members are good Object Oriented design. They both break OOP Encapsulation by exposing an objects data to the world that probably shouldn't be accessing the properties of the object in the first place.
This is done by applying the encapsulation principle of OOP.
A language mechanism for restricting access to some of the object's components.
This means, you must define the visibility for the attributes and methods of your classes. There are 3 common visibilities:
Private: Only the class can see and use the attributes/methods.
Protected: Only the class and its children can see and use the attributes/methods.
Public: Every class can see and use the attributes/methods.
When you declare private/protected attributes, you are encouraged to create methods to obtain the value (get) and change the value (set). One example about visibility is the [ArrayList][2] class: it has a size property to know the actual size of the inner array. Only the class must change its value, so the code is something like
public class ArrayList<E> {
private int size;
private Object[] array;
public getSize() {
return this.size;
}
public void add(E element) {
//logic to add the element in the array...
this.size++;
}
}
In this example, you can see that the size value can change only inside the class methods, and you can get the actual size by calling it in your code (not mutating it):
public void someMethod() {
List<String> ls = new ArrayList<String>();
//adding values
ls.add("Hello");
ls.add("World");
for(int i = 0; i < ls.size(); i++) {
System.out.println(ls.get(i));
}
}
Getters and setters encapsulate the fields of a class by making them accessible only through its public methods and keep the values themselves private. That is considered a good OO principle.
Granted, it often seems like redundant code if it does nothing more than setting or returning a value. However, setters also allow you to do input validation or cleanup. Having that in one place improves data integrity for your objects,
Because we are using Object oriented programming language.
Here we are using Data hiding and encapsulation.
The variable should not directly accessible from out side world (for achiving data hiding) so we will create it private so
shape.x
is not correct.
Getter and setter method are used to get and set the value of x which is the way to achive encapsulation.