Private Final
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Private Final
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Private vs Final Access Modifier in Java
// Java Program to illustrate Private Access Modifier
private void m1() { System.out.println( "GFG" ); }
public static void main(String[] args)
// creating an object of type class A
// accessing the method m1()
// Java program to illustrate Final keyword
System.out.println( "Rahul " );
public final void surName()
System.out.println( "Trivedi" );
System.out.println( "Sharma" );
public static void main(String[] args)
System.out.println( "GFG" );
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Whenever we are writing our classes we have to provide some information about our classes to the JVM like whether this class can be accessed from anywhere or not, whether child class creation is possible or not, whether object creation is possible or not etc. we can specify this information by using an appropriate keyword in java called access modifiers. So access modifiers are used to set the accessibility of classes, methods, and other members.
This modifier is not applicable for top-level classes or interfaces. It is only applicable to constructors, methods, and fields inside the classes. If a variable or methods or constructor is declared as private then we can access them only from within the class i.e from outside the class we can’t access them.
It is a modifier applicable to classes, methods, and variables. If we declare a parent class method as final then we can’t override that method in the child class because its implementation is final and if a class is declared as final we can’t extend the functionality of that class i.e we can’t create a child class for that class i.e inheritance is not possible for final classes. Every method present inside the final class is always final y default but every variable present inside the final class need not be final. The main advantage of the final keyword is we can achieve security and we can provide a unique implementation. But the main disadvantage of the final keyword is we are missing key benefits of OOPs like Inheritance(Because of the final class), Polymorphism(Because of the final method) hence if there are no specific requirements then it is not recommended to use the final keyword.
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This modifier is not applicable to top-level classes.
This modifier is applicable to top-level classes.
We cannot access private methods outside the class.
We can access the final method outside the class.
This modifier is applicable to both the enum and constructor.
The final modifier is not applicable to both the enum and constructor.
This modifier is not applicable for local variables.
The final modifier is the only modifier which is applicable for local variables.
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My question is simple. Which approach is more efficient?
As I see the DI in the method2 is more recent. But I wanted to ask you which one should I use?
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TL;DR: Method 2 is much more flexible.
Method 1 is an example of field injection and method 2 is an example of constructor injection.
Field injection has some drawbacks that constructor injection avoids. Here are some advantages of constructor injection:
So, Spring offers constructor injection:
Immutability is sometimes preferred. One reason is that it helps with thread-safety.
Personally, I follow the rule, "if it can be final, it should be final."
You won't need reflection to set the dependencies. Yes, many mocking frameworks handle this for you, but with constructor injection, you have the option to call new on the constructor.
An object is created by calling its constructor, right? We usually want our arguments to be non-null at the time they are passed in. With constructor injection, the Spring IoC container makes sure that all the arguments passed in the constructor are available before passing them into the constructor.
use constructor injection, Spring also recommends it
In your main code, you should use method 2 as field injection (method 1) is not recommended. (see here for reasons)
In your test code, it's okay to use method 1.
In addition to what the other answers have said about immutability, another benefit of constructor injection is to be able to avoid NPE is the field is not initialized. Using autowired, from a test, you’d create the class and then must remember to set the field. Using constructor injection, you can’t not initialize the field. This is more prominent in Kotlin where autowired fields are declared as lateinit var and throw a runtime exception if used before initialized. But a constructor argument can be declared as not null type which prevents you from even explicitly passing null.
I suggest you suggest something better. By using the Lombok library's @RequiredArgConstructor you are thus avoiding the boilerplate code. and if you wonder why @Autowired not reccomended , because of when you want to write unit testing in your application and there will be problem , where if you use @Autowired .
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I just would like to clarify this. What is the difference between -
Jon Skeet explained as "not related to a particular instance at all", ok I think I understand it. Then what does final do in this case exactly?
Below code does not work is it because student age is assigned as static final? Does it mean the default age can not be overwritten at all? then is it possible to create the constructor that specify an age other than the default?
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static means "not related to a particular instance at all" - final means you cannot change this value after initialization and this value must be initialized.
The combination of final and static gives you the ability to create constants. This is no longer recommended in a public way (totally ok for e.g. magic numbers in a private context) as it's not typesafe. Use Enum post java 1.5 or create your own typesafe enums pre java 1.5 as suggested in Joshua Blochs Effective Java and this question.
Remark: reading this about a year later, I think I need to emphasize that there is nothing wrong with public static final fields in general, just that named constants should be implemented with enums or another type safe alternative.
Once a variable is declared final , its value cannot be changed later. In the code sample you provided, a constant is declared for defining the age of a student for a particular activity. It might mean that there will be a condition where for certain activity, the age of the student will be compared with this constant. If the age of student is greater than 18, then only he will be allowed to proceed or not.
It's constant declaration. You can't change the value.
It's a static declaration but not constant. The value can be changed.
final variables can only be initialized once.
The final modifier on a field signifies that the field's value cannot be modified once initialized.
Because of this, you cannot set STUDENT_AGE = age; unless it's non-final.
To simply say, the modifier final means its FINAL. you can not change the value once its defined.
And coming to your requirement, if you want to provide default age if nothing is provided, then simply remove final modifier for the variable STUDENT_AGE. just what @Quoi said
final static variables can only be initialized once, but not necessarily at the time of declaration.. But once it is initialized, it's value cannot be changed.. So, you can initialize your final static variable, at the time of declaration or in static block.
Now, a static variable (also called, class variable), is not specific to any instance. It is shared among all the instances of that class..
See this way, Static variables are loaded into memory when the class is first time loaded.. That's why it is shared by all the instances. So any change in static variable
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