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Purpose of getters/setters in this class [duplicate]

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Why use getters and setters/accessors?
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Closed 7 years ago.
In this class, I have the constructor take in 4 parameters. And the values are initialized appropriately. Set int imageid to mImageId, etc..
What is then the purpose of the sequence of getters/setters if the member variables are initialized by the parameters?
From what I've read. getters/setters for every field or member variable essentially makes the class "public". Or is the purpose of getters/setters to broadcast some "intent" to another class?
public class Page {
private int mImageId;
private String mText;
private Choice mChoice1;
private Choice mChoice2;
public Page(int imageId, String text, Choice choice1, Choice choice2 ){
mImageId = imageId;
mText = text;
mChoice1 = choice1;
mChoice2 = choice2;
}
// start of getters/setters
public int getImageId(){
return mImageId;
}
public void setImageId(int id){
mImageId = id;
}
public String getText() {
return mText;
}
public void setText(String text) {
mText = text;
}
public Choice getChoice1() {
return mChoice1;
}
public void setChoice1(Choice choice1) {
mChoice1 = choice1;
}// Choice 1
public Choice getChoice2() {
return mChoice2;
}
public void setChoice2(Choice choice2) {
mChoice2 = choice2;
}// Choice 2

This is a mutable class, meaning that even though initial state is set upon instantiation, it can always be changed without creating a new instance.
You might think that this is a JavaBean, but since it doesn't expose a no-arg constructor, nor do the names of the getters or setters match the names of the fields, it's not strictly following the convention.

A setter lets you change the value of a variable later on.
A getter lets you access the value of a variable from another class.
In your context, I suppose Page describes some page content. Now, suppose you pass that Page object to some sort of layout class, it will use the getters to access the values of the variables to render the layout. As the variables are declared as private, there is no other way to access them, except for using the getter methods.

You may still need to set member variables after the object was constructed.
If you don't implement setters this will effectively make the class immutable which might be wanted behaviour in some situations as well.
So well, it depends on your needs in specific situation, the setters are not something mandatory. For getters - yes, if you want to read the content of object, this is common way. But it doesn't need to be 1:1 to member variables.
PS: I suggest avoiding those "m" prefixes, this is very uncommon in Java, doesn't provide any real value and makes the code less readable.

getters/setters make a JavaBean out of plain POJO .
There are many frameworks that use the Bean standard to create/manipulate Java Objects.
For instance, an ORM framework can create Beans from an SQL query, JAX-RS framework can create Beans from an HTTP request, etc.
NOTE: the Java Bean standard requires a default no-arg constructor.

There is no Problem you can choose any sequence of setter's/ getter's according to you.
The "public" keyword is used by java compiler (javac) to access the class that containing main method.
But in case of java bean the classes are generally placed in packages for proper hierarchy, so to access these classes from different packages we need to make class "public".

Are there any plans for Java to add implicit Getters and Setters?

Does anyone know if there is a plan to add in implicit getters and setters for Class variables?
I'm thinking of the current Scala code that allows this already. Something like the following, where if you don't define a getter/setter it uses the value, but if you do define a getter/setter for the value it uses that instead of a direct variable call.
class A{
int value = 3;
}
class B{
int value = 3;
public int value(){
return value;
}
}
// in some method
A a = new A();
System.out.println(a.value);
B b = new B();
System.out.println(b.value); // <-- no () for accessing value even though it uses the getter

not Java per se, but there is this Project Lombok

Foreword: maybe I'm wrong but the question is maybe a better fit for java platform user/devel lists, like those at http://www.oracle.com/technetwork/java/javase/community/index.html
I suppose you'll receive more meaningful answers there, and less speculation.
My own take on the subject is that the JavaBean model is far too established to admit any significant change for backward compatibility, and that java encapsulation model is based on the concept that you hide fields with private access and provide accessors/mutators.
If you only want to expose members you can simply make them public.
Translating fields to automatic accessor/mutator methods is quite a big change to the language, and would probably create much confusion for little gain.
You should also consider that the scala choice implies a radically different approach to member access, for the sake of uniform access principle.

A simple getter returns a field value. However a getter can also return the results of an operation:
public boolean isError()
{
return errorList.size() > 0;
}
Similarly a setter might do other operations:
public void setName(String name)
{
this.name = name;
this.sortName = name.toLowerCase();
}
So other than the bean paradigm, and for the sake of consistency, getters/setters should be used rather than direct field access.

Java 14 (LTS release) has records, but you need to compile with additional options for it to work. Records provide getters for the constructor params and aim to solve a few other problems inherent in earlier versions.

Must I use a getter method inside of my own class in Java?

Say I have some class:
public class A {
private int val = 0;
public int getVal() {
return val;
}
public void addFrom(A otherA) {
this.val += otherA.val;
if (otherA.val > 0)
otherA.val = 0;
else
otherA = Math.abs(otherA.val);
}
}
Should I be using getter methods instead to use otherA's val variable? Is it better style to do so?
Edit: This is a very simplified version of a class that takes much too long to read. But assume that there IS lazy initialization going on, that there are other methods that access this class, etc. I have updated the example method so that this may be more clear, but I hope it is clear that my question involves accessing the other object's variables, and want to know if it is faux pas to use a direct variable access for something that is not "this".

No, absolutely not.
You should use the variable directly when you're inside the class' members, and use getters in every other situation (when you would get an error because val is private anyway).

public int getVal() is intended to present your gift(variable) within a box to the outside world (encapsulation). Do you give gifts yourself in a box? It's weird, so use the variable as it is.

You can use variables, but the current code does not compile. Probably, the return should be int instead of boolean.
Probably, your intention is to override the compareTo method from the Comparable interface

Adding an unnecessary getter reveals internal structure and this is an opportunity for increased coupling.
A truly well-encapsulated class has no setters and preferably no getters either. Rather than asking a class for some data and then compute something with it, the class should be responsible to compute something with its data and then return the result.
Use of accessors to restrict direct access to field variable is preferred over the use of public fields, however, making getters and setter for each and every field is overkill. It also depends on the situation though, sometimes you just want a dumb data object. Accessors should be added for field where they're really required. A class should expose larger behavior which happens to use its state, rather than a repository of state to be manipulated by other classes.

Java Conventions: use getters/setters WITHIN the class?

My professor really emphasizes protecting against privacy leaks by always using accessors and mutators to access private instance variables; however, do I have to use the getters/setters of a class within the class?
So for instance, if I have the following class:
public class Person
{
private String name;
private int age;
}
and I want to write a toString() method for it. Can I just write:
public String toString()
{
return name + " " + age;
}
OR do I need to do something like this:
public String toString()
{
return this.getName() + " " + this.getAge();
}

You CAN do either one. However, your professor might appreciate using the methods instead of the direct access. Here's why.
Let's say you have a class like this:
class SomeClass {
private int someValue;
private String someString;
public SomeClass(int someValue, String someString) {
this.someValue = someValue;
this.someString = someString;
}
public int someValue() {
return this.someValue;
}
public String someString() {
return this.someString;
}
public String toString() {
return someValue + ": " + someString;
}
}
It's pretty straightforward, right? Well, what if all of a sudden we want to CHANGE the implementation of how we calculate someValue, and base it off of someString:
public int someValue() {
int value = 0;
for(int i = 0; i < someString.length; i++) {
if(someString.charAt(i) == ' ') value++;
}
return value;
}
Now you also have to change every place where variable someValue was used.
So if you want to make the code easier to maintain in the long run, use the methods calls. This way when you code changes on you (and trust me, it changes all the time) you only have to change it in one spot instead of two.
And yes, you would want to use a method call in getting someString instead of the direct access in the last method :-)

When I design a class I try to make a clear distinction between the inside (implementation details) and the outside (the interface exposed to the world). Getters and setters provide a convenient place to convert values between the form in which they are stored in the object’s instance members and the form in which the outside world sees them. Using getters and setters internally would muck that up, because they'd be getting used by both the inside and outside.
If you find yourself wanting to hide part of a class from another part of the same class, consider breaking off the part you want to hide into its own class.

It's normally not a good idea, for a number of reasons:
You may not even want accessors for all fields
Some accessors may make a defensive copy so not to expose internal state, this is normally unnecessary within the class where you know that you are not going to modify it - or plain wrong if you know you ARE going to modify it
It makes debugging more annoying, because you have to follow the getters / setters
It makes reading the code harder in most IDEs, since most of them color fields differently than local variables
... but as always, there are exceptions. Some setters may have side-effects (for example setting a second value) that you WANT to execute, then it might be better to use the setter. Also, if you design your class for inheritance, it may be better to go via an accessor if you want the subclass to be able to alter the behavior.

In general, no. If your getter returns something other than the value of the field then you should use the method, but in that rare case your method should have a more descriptive name. For a bad example, if you have:
public void setName(String name)
{
_name = name;
}
and your getter returned something else, like
public String getName()
{
return _name.toUpperCase();
}
then yes, you should use the getter. It would be better, though, to have a more descriptive name for that getter:
public String getNameAsUppercase()
{
return _name.toUpperCase();
}

You can use the accessors and mutators, but its a messy standard to follow.
It clutters up your code and confuses anyone trying to read it thinking it might not be a part of your class.
Basically, just access the variables directly from inside your class, and indirectly from anywhere else.

On the flip side, consider it from a design standpoint. One of the motivations for getters/setters is that the underlying data storage can change and things that implement the class won't need to be changed since it is encapsulated.
So, keeping that in mind, using getters/setters within the class makes future changes easier. Instead of having to find all the places that alter the member directly, you just have to change the getter/setter. Depending on the complexity of the class, this may significantly reduce the amount of work it takes to change the storage members.
For example, let's assume you start out with the age variable in years. Then you decide later to store it as seconds for some reason. But you want to always print it in years anyway. So in your example, you could do the math in your toString() function (and anywhere else that wants years as the units) or you can just change the math in the getAge() routine to return years from the seconds and nothing else has to change.
Obviously that example is a bit trivial. The more complicated the class, the more useful it is to use getters/setters within it.

No, you don't. You can access any variables, private, public or protected, from within the class.
Here are some tables to help you:
Source: Java Tutorials

If your class (or the accessor methods in question) is not final, then you should definitely use the accessor methods.
If another class extends yours and overrides those accessors, your class should use the overridden accessors. If this would break your superclass, then your superclass is designed incorrectly; prevent those accessors from being overridden with final, or change the design of your class.

No you can use directly your instance variables inside the class, you're not violating any "rule". Getters and setters are mandatory for others classes to access instance variables of a class to not violate the encapsulation principle (which is quite important in OO programming).
In the end it's a matter of choice, but you're saving one method call using your first example.

I think we should use getters() and setters() instead of accessing directly. It is also makes debugging very easy; for example, if you need to assign a variable to multiple place in your class and later want to find out from how many places the variable is assigned to, then you need to find all the assignment and set the break point.
However, if you use a setter you can simply put a break point inside the setter method and can see how many time the variable is assigned.

I use a mix of both. Accessor methods add more clutter so I use them only when the variable is used many times. If the variable is used only once or twice I don't use them.

What is a good practice to access class attributes in class methods?

I always wonder about the best way to access a class attribute from a class method in Java.
Could you quickly convince me about which one of the 3 solutions below (or a totally different one :P) is a good practice?
public class Test {
String a;
public String getA(){
return this.a;
}
public setA(String a){
this.a = a;
}
// Using Getter
public void display(){
// Solution 1
System.out.println(this.a);
// Solution 2
System.out.println(getA());
// Solution 3
System.out.println(this.getA());
}
// Using Setter
public void myMethod(String b, String c){
// Solution 1
this.a = b + c;
// Solution 2
setA(b + c);
// Solution 3
this.setA(b + c);
}
}

That entirely depends on what the getters and setters are doing. If they do more than just getting and setting the value (which should be explicitly documented in the method's Javadoc), then it would really make difference what way you'd choose from inside the class. But if they are pure Javabean like getters/setters, then I'd rather access the variable directly by either a or this.a depending on whether there's a local variable in the scope with exactly that name.
Personally I would just keep the getters and setters "pure" according the Javabean spec and add another getter or setter with a self-explaining method name whenever I'd like to do something more than just getting/setting the value. E.g. getAndIncrement(), getAsString(), setAsInt(String), etc.
Matter of taste. It won't really harm as long as you're consistent with it throughout your coding.

If you need to create any validation in the future you'll want a setter/getter . When you make a variable visible you brake the class encapsulation. In theory it means that your code is not so Object Oriented :P , but in practice you lose the ability to do a lot of code refactorings. For example, extracting a interface.
And for the this call, I think its redundant, but that's just me :)

I use getters and setters in a class if there is more logic involved that just returning this.value. This way I avoid duplication. An example:
...
public List<String> getList() {
if (this.list == null) {
this.list = new LinkedList<String>();
}
return this.list;
}
public int getListSize() {
return getList().size();
}
...
I always use "this" because it makes it easier for other people to read my code. There is no doubt that this.value is a class attribute, whereas value can be both a local variable and a class attribute.

Solution 2 or 3 are best practice as they provide encapsulation to the field. For example, what if the field 'a' is a user's postcode and your application has a new requirement to always return the postcode as uppercase. With solutions 2 or 3 this becomes trivial. E.g.
private String postcode;
public String getPostcode()
{
return postcode;
}
becomes
private String postcode;
public String getPostcode()
{
return postcode != null? postcode.toUppercase() : null;
}
and you will only have made the change in one place instead of anywhere where the field is accessed. The addition of this is purely up to your own personal style or project standards. Personally, I don't like it as it is unnecessary and just gets in the way of readability, but for others it makes the owner of method/field clearer.

Using setA(b + c) is silly.
Getters and setters are part of the interface. Methods already have full access to the state. Be frank about it.
If you're worried that you might break an invariant then your class is too complex for you. (Admit it and refactor.)

Using getters and setters is the way to go.
It's commonly accepted practise
So other programmers are more likely to understand your code.
It gives the class author options in the future
Say you want to prevent someone setting a to null. Expose the member and you can never do it.
As for whether to use this - I try to use this consistently to make it very clear to anyone else which are instance members and which are local variables at any point - also helps avoid accidental shadowing, but I think this is less important and more a style thing.
Also - this.a is an instance member (one per instance) not a class member (one-per-class, would be static). Another reason to use this to be clear.

I would go with
System.out.println(getA());
and
setA(b + c);
for the simple reason that if you wanted to generally change the way an attribute is accessed or enforce any constraints as to what you could set a variable to, you can just change the getA or setA methods.
I don't like using this unless I need to explicitly distinguish between variables of the same name.