final variable initialization in derived class

final variable in java
java final variable in method
final class can be inherited
a final class cannot extend other classes
final class in java
final method in java
can we change final variable value in java
what is the usage of a blank final variable

I am confused if we can initialize the final variable of the base class in its derived class. My base class is

    abstract class MyClass1 {
        //Compiler Error:Variable is not initialized in the default constructor.

        public final int finalVar;
    }
    //And my derived class with variable initialization.

    class DerivedClass extends MyClass1 {
        DerivedClass()
        {
            super();
            //Cannot asssign a value to finalVar.
            finalVar = 1000;
        }
   }

Please tell me if it is possible to initialize the final variable in the derived class. Will it just give a compile time error or also will a runtime error?

A final variable needs to be initialized in the constructor, which your abstract class lacks. Adding that constructor then allows you to call it via super(). Consider the following example:

public class Main {
    public static void main(String[] args) {
        baseClass instance = new derivedClass(1);
    }
}

abstract class baseClass {
    protected final int finalVar;
    baseClass(int finalVar){
        this.finalVar = finalVar;
    }
}

class derivedClass extends baseClass {
    derivedClass(int finalVar){
        super(finalVar);
        System.out.println(this.finalVar);
    }
}

final keyword in java, A blank final variable can be initialized inside instance-initializer block or inside constructor. If you have more than one constructor in your class then it must be initialized in all of them, otherwise compile time error will be thrown. A blank final static variable can be initialized inside static block. Each derived class would then have the opportunity to initialize that variable, potentially changing its value! By restricting the initialization of variables to the constructor of the class those variables belong to, C++ ensures that all variables are initialized only once.

You must assign a value to your variable in the parent class.

// Declaring Parent class
class Parent {
    /* Creation of final variable pa of string type i.e 
    the value of this variable is fixed throughout all 
    the derived classes or not overidden*/
    final String pa = "Hello , We are in parent class variable";
}
// Declaring Child class by extending Parent class
class Child extends Parent {
    /* Creation of variable ch of string type i.e 
    the value of this variable is not fixed throughout all 
    the derived classes or overidden*/
    String ch = "Hello , We are in child class variable";
}

class Test {
    public static void main(String[] args) {
        // Creation of Parent class object
        Parent p = new Parent();
        // Calling a variable pa by parent object 
        System.out.println(p.pa);
        // Creation of Child class object
        Child c = new Child();

        // Calling a variable ch by Child object 
        System.out.println(c.ch);
        // Calling a variable pa by Child object 
        System.out.println(c.pa);
    }
}

Using final with Inheritance in Java, We can declare variables, methods and classes with final keyword. Using final with inheritance. During inheritance, we must declare methods with final keyword � final variables are initialized at the time of declaration and they cannot be re initialized or modified later in the child class. final in java means constants. Trying to modify their values causes compilation error.

Final members need to be initialized in the constructor of the class. You can modify your code to have the subclass pass the value via the constructor:

abstract class MyClass1 {

    public final int finalVar;

    protected MyClass1(int var) {
         finalVar = var;
    }

} 

class DerivedClass extends MyClass1 {
    DerivedClass() {
        super(1000);
    }
}

11.4 — Constructors and initialization of derived classes, However, C++ prevents classes from initializing inherited member variables in the different than setting the data members of Fruit and Apple classes constant ? static final variables are initialized when the class is loaded. The constructor may be called much later, or not at all. Also, the constructor will be called multiple times (with each new object ), so the field could no longer be final. If you need custom logic to initialize your static final field, put that in a static block

Final Keyword In Java, We must initialize the blank final variable in constructor of the class otherwise it will That shows that final methods are inherited but they are not eligible for� A local variable declaration - with or without initialization - is a statement, as specified in section 14.4 of the JLS. It's important to note that this is not an expression in the way that a simple assignment expression is - you can't use it as part of a larger statement (other than a block).

What is the final keyword in Java?, This entity can be - but is not limited to - a variable, a class or a method. final If it's declared but not yet initialized, it's called a blank final variable. class Base{. final is a keyword in java used for restricting some functionalities. We can declare variables, methods and classes with final keyword. Using final with inheritance During inheritance, we must declare methods with final keyword for which we required to follow the same implementation throughout all the derived classes.

Final Keyword in Java, Inheritance enables us to reuse the existing code but sometimes we want to We should initialize a final variable in Java, otherwise, a compiler can throw a� Before Python Initialization¶. In an application embedding Python, the Py_Initialize() function must be called before using any other Python/C API functions; with the exception of a few functions and the global configuration variables.

Comments
  • Is it just give the compile time error or also will give the runtime error. - if your code doesn't pass compilation, you can't run it, so there will be no runtime for this code.
  • You should refer to the final variable declaration documentation!
  • Doesn't the compilation error make it clear that the final field must be initialized by the base class constructor(s)?
  • Why have you not run this and found the answer for yourself?