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Can you call an abstract method from a non abstract method in java?
We can't call (i.e, execute) an abstract method in java because these methods don't contain any code to execute!In some special cases like when an abstract method is overridden in a subclass, and when we are using super class reference variable( which is referring that subclass object), it appears that we are calling abstract method in super class. But actually the code in the subclass method is being executed.Example:abstract class SuperClass{abstract void show(); //abstract method in super class}class SubClass extends SuperClass{void show(){ //show() of SuperClass overridden in SubClassSystem.out.println("SubClass Method");}}class Example{public static void main(String... args){SuperClass sup=new SubClass();sup.show(); //SubClass show() will be executed !!!}}
What is concrete class in java?
A method which is not abstract i.e. if a methods definition is given in the same class its declared is called concrete. where as abstract method would have no definition till the deep down of the hierarchy of class structure but ll ve a declaration in all the subclasses and definition in one subclass after which it need not be declared in the further subclasses. By the way defining the abstract method in a subclass would end the carrying of the declaration till down, but defining it is not mandatory where declaring is mandatory.
What is true about true about abstract data type Object of an abstract class type cant be created. We can derive classes from these abstract classes Object of an abstract class t?
True - an instance of an abstract class cannot be created. False - derive (subclass) from a class, not the object (the instance).
Can abstract class have constructors?
A constructor of a class in invoked when a object of that class is created. As an abstract class can't have an object, so we can't create a constructor of the abstract class. But we can create a constructor of a concrete subclass of that abstract class and we have to pass the object of that concrete subclass to the abstract class.
Is every class in java is subclass of itself?
A class can be a subclass of another class, not of itself.A class can be a subclass of another class, not of itself.A class can be a subclass of another class, not of itself.A class can be a subclass of another class, not of itself.
Can you instantiate an abstract class?
No. You must create a subclass of the abstract class in order to be able to instantiate it.
Can you call an abstract method from a non abstract method in java?
We can't call (i.e, execute) an abstract method in java because these methods don't contain any code to execute!In some special cases like when an abstract method is overridden in a subclass, and when we are using super class reference variable( which is referring that subclass object), it appears that we are calling abstract method in super class. But actually the code in the subclass method is being executed.Example:abstract class SuperClass{abstract void show(); //abstract method in super class}class SubClass extends SuperClass{void show(){ //show() of SuperClass overridden in SubClassSystem.out.println("SubClass Method");}}class Example{public static void main(String... args){SuperClass sup=new SubClass();sup.show(); //SubClass show() will be executed !!!}}
Give an example of abstract class and its subclass?
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What is concrete class in java?
A method which is not abstract i.e. if a methods definition is given in the same class its declared is called concrete. where as abstract method would have no definition till the deep down of the hierarchy of class structure but ll ve a declaration in all the subclasses and definition in one subclass after which it need not be declared in the further subclasses. By the way defining the abstract method in a subclass would end the carrying of the declaration till down, but defining it is not mandatory where declaring is mandatory.
What is true about true about abstract data type Object of an abstract class type cant be created. We can derive classes from these abstract classes Object of an abstract class t?
True - an instance of an abstract class cannot be created. False - derive (subclass) from a class, not the object (the instance).
Can abstract class have constructors?
A constructor of a class in invoked when a object of that class is created. As an abstract class can't have an object, so we can't create a constructor of the abstract class. But we can create a constructor of a concrete subclass of that abstract class and we have to pass the object of that concrete subclass to the abstract class.
Is every class in java is subclass of itself?
A class can be a subclass of another class, not of itself.A class can be a subclass of another class, not of itself.A class can be a subclass of another class, not of itself.A class can be a subclass of another class, not of itself.
Difference between abstract and final class?
Abstract class is built to promote inheritance whereas a final class is built to avoid inheritanceAn Abstract class can be extended by another class whereas a final class cannot be extended
When the class b is inherited from class a class a is called what?
Class B is said to be a "subclass" of class A.
Write a Java Program to illustarte the use of abstract methods?
Abstract MethodsAn abstract method is a method that's been declared as abstract but not implemented. In other words, the method contains no code. You mark a method abstract when you want to force subclasses to provide the implementation. (remember the reason why you would want to make a class abstract from the previous paragraph)Ex: public abstract void showSample();Notice that the abstract method ends with a semicolon instead of curly braces. It is illegal to have even a single abstract method in a class that is not explicitly declared abstract! Look at the following illegal class:public class IllegalAbstractClass{public abstract void test();}The preceding class will produce the following error if you try to compile it:IllegalClass.java:1: class IllegalAbstractClass must be declaredabstract.It does not define void test() from class IllegalAbstractClass.public class IllegalAbstractClass {1 errorYou can, however, have an abstract class with no abstract methods. The following example will compile fine:public abstract class LegalAbstractClass{void test() {// you can write lots of code here}}In the preceding example, test() is not abstract. Three different clues tell you it's not an abstract method:• The method is not marked abstract.• The method declaration includes curly braces, as opposed to ending in a semicolon. In other words, the method has a method body.• The method contains actual implementation code.Any class that extends an abstract class must implement all abstract methods of the superclass, unless the subclass is also abstract. The rule is this:The first concrete subclass of an abstract class must implement all abstract methods of the superclass.Concrete just means nonabstract, so if you have an abstract class extending another abstract class, the abstract subclass doesn't need to provide implementations for the inherited abstract methods. Sooner or later, though, somebody's going to make a nonabstract subclass (in other words, a class that can be instantiated), and that subclass will have to implement all the abstract methods from up the inheritance tree.
What happens if an abstract modifier is applied to class. Explain?
The classes which have one or more abstract methods are abstract. To declare a class as abstract, use the abstract keyword in front of the class keyword, before the class declaration. Abstract classes cannot be instantiated. Similarly the new keyword cannot be used to create an object of the abstract class. Remember that the constructors and static variables cannot be declared as abstract. Any subclass of an abstract class must either implement all of the abstract methods in the superclass or be itself declared abstract.
Why we can't create object for Container class using new keyword?
It is an abstract class so you can't instantiate it directly, but have to use a subclass instead.
