This question already has answers here:
Are static methods inherited in Java?
(15 answers)
Closed 8 years ago.
I was able to run the following code:
class A
{
public static void display()
{
System.out.println("Inside static method of superclass");
}
}
class B extends A
{
public void show()
{
display();
}
}
public class staticMethodInheritance {
public static void main(String[] args) {
B b = new B();
b.display();
}
}
Now I was able to access the method display() from the instance of the class B then why is it said that static methods cannot be inherited. If I declare a method display in class B then it is said that the method in the superclass is hidden and the method in the child class is called then again isnt this the behavior that is desired when we override a method.
The only difference with inherited static (class) methods and inherited non-static (instance) methods is that when you write a new static method with the same signature, the old static method is just hidden, not overridden.
Static methods are inherited but cannot be overriden they can be re- defined.
Related
This question already has answers here:
Is method hiding a form of Polymorphism?
(5 answers)
Closed 4 years ago.
I read somewhere that overriding an static methods can not be considered polymorphism. Just hiding the method. What does it mean "hide"?
public class TesterClass {
public static void main(String[] args) {
ClassLetters.staticM();
ClassA.staticM();
ClassLetters Lettersobj = new ClassA();
ClassA Aobj = new ClassA();
Lettersobj.staticM();
Aobj.staticM();
ClassA aa = (ClassA) Lettersobj;
aa.staticM();
}
}
Output:
Static Method Called in CLassLetters
Static Method Called in ClassA
Static Method Called in CLassLetters
Static Method Called in ClassA
Static Method Called in ClassA
classA inherits ClassLetters with same static void classM. Why it is not polymorphism?
You can't override static members, because they are not inherited. They belong to the class itself, period.
If you create a subclass, and you create a (new) static method with the same name/parameters/... you don't override the original one, you re-define a new one.
So, the static method in your original class is not overridden, but hidden.
This question already has answers here:
Why doesn't Java allow overriding of static methods?
(22 answers)
Is it possible to override a static method in derived class?
(6 answers)
Closed 5 years ago.
class B extends A {
static public void printMe(){
System.out.println("in static B");
}
}
class A{
static public void printMe(){
System.out.println("In static A");
}
}
public static void main(String[] args) {
A a = new B();
a.printMe();
}
Why is the output "In static A" ?
Static members bind to type rather than implemented type. Hence you see the methods executing from class A.
And static members are not to be ovverriden and they share same copy regardless of instance state.
If you need methods to be ovveriden, do not use them as static members.
Static member or method belongs to class level instead of specific instance.
A static class will have only 1 instance even if you create multiple instance or do not create instance.
In your case, since you have created instance of class A, method inside class A is implemented.
Another way to get a clear concise for the problem scenario is try running the code mentioned below:
public static void main(String[] args) {
A.printMe();
}
You will get clear idea.
This question already has answers here:
What is the difference between static and default methods in a Java interface?
(12 answers)
Closed 5 years ago.
interface TestInterface
{
public static void square(int a)
{
System.out.println("Square is "+a*a);
}
public static void show()
{
System.out.println("Default Method Executed");
}
}
class TestClass implements TestInterface
{
public void square(int a)
{
System.out.println(a*a);
}
public void show()
{
System.out.println("Overridden Method");
}
public static void main(String args[])
{
TestClass d=new TestClass();
d.square(4);
TestInterface.square(4);
TestInterface.show();
d.show();
}
}
I have a doubt in my code. I learnt that static methods cannot be overridden in JAVA, but it seems to be working fine here.
When i give both default and static keywords together, like this
interface TestInterface
{
default static void square(int a)
{
System.out.println("Square is "+a*a);
}
public static void show()
{
System.out.println("Default Method Executed");
}
}
An error crops up as follows:
illegal combination of modifiers: static and default
What is the reason for JAVA treating this as an error?
A static method is meant to be called without an instance of the class/interface concerned. Usually they are meant to be utility methods.
A default method is meant to be called on an instance of the interface concerned. All implementations of this interface will have this method definition, unless it is overridden.
The reason these two terms are not allowed together is simply because they contradict each other: default requires an object, static requires no object.
TestClass.show() and TestClass.square() are not static and therefore do not override the static methods in the interface. They are member methods and require an object to call them. On the other hand, the methods with the same name in the interface are static and so you can call them with the interface name or class name without an object.
This question already has answers here:
Is it possible to override a static method in derived class?
(6 answers)
Closed 7 years ago.
lets assume that i have 2 classes.
ParentClass:
public class ParentClass {
public static void getInstance(){
System.out.println("Parent method");
}
}
ChildClass:
public class ChildClass extends ParentClass {
public static void getInstance(){
System.out.println("child method");
}
public static void main(String args[]){
ParentClass pc=new ChildClass();
pc.getInstance();
}
}
as you notice above both classes has a static method called getInstance() and in java and many other languages if there is an inherited method and you have the same method in the child class the method that get executed is one in the child class.
the question is: why pc.getInstance(); calls the method in the parent class? yeah there is no method overriding for static methods but could anyone please explain more the weird behavior of pc instance and why does it refer to the parent method even tho its pointing on the child class??
and why is it allowed to call a static method with a reference to an instance of the class ?
Thanks
There is no method overriding for static methods. The static type of the instance being used to call the method (ParentClass in your example) determines which method is called.
Besides that, it's bad practice to use an instance reference in order to call a static method. You should use ClassName.methodName() to execute a static method.
This question already has answers here:
Static methods and their overriding
(5 answers)
Closed 8 years ago.
What should be printed when we execute this code?
I picked the question from here where the answer is provided but I kinda believe is wrong. First the call to a static function has to be done in static way, second when we override a static function the previous one is no longer accessible ( no new memory is assigned)
class Base {
public static void show() {
System.out.println("Base::show() called");
}
}
class Derived extends Base {
public static void show() {
System.out.println("Derived::show() called");
}
}
class Main {
public static void main(String[] args) {
Base b = new Derived();;
b.show();
}
}
static method belongs to class itself and overriding works for instance methods only. If you define the same method again in sub-class then it's called re-defining hiding of the static method.
static method looks for class to invoke it and that can be verified by below same code:
Base b = null;
b.show(); // Base::show() called
It doesn't make any sense to call static method via object.