CODEWITHSUNDEEP
javaclassabstract-class
EX3QTE
EX3QTE

Reputation: 3

Is this code valid in Java?

Just had this in a unit test. So:

abstract class A {...}

class B extends A {...}

A a = new B();

Pretty much doubt it's viable, but I'm totally confused at the moment. The content of the classes is irrelevant.

Upvotes: 0

Views: 113

Answers (6)

Jon Paul
Jon Paul

Reputation: 1

Interface - every method is always public and abstract whether you are declaring it or not. You can’t declare an interface method with the following modifiers. Every variable present inside interface is always public static and final whether we are declaring or not. You can’t declare an interface variable with the following modifiers, private, protected, transient and volatile. The variables present within abstract class don’t have to be public, static and final. There are no restrictions on abstract class variable modifiers. For abstract class variable are not required to perform initialization at the time of declaration. An abstract class can declare instance and static blocks. Inside interface we can’t declare instance and static blocks otherwise we will get compile time error. Interface can’t declare constructors. Just keep these fun facts in mind.

Upvotes: 0

Pankaj Sharma
Pankaj Sharma

Reputation: 1853

yes this concept is known as polymorphism in java . a parent can contains reference of child class. and parent can be either interface or abstruct class. even you need not to cast . for example . 

a animal can be horse or cat  , here animal is an interface or abstract class.

i recommend (SCJP Sun Certified Programmer -kathy sierra)book has lot of concepts related to java language.

Upvotes: 1

Rohit Srivastava
Rohit Srivastava

Reputation: 91

Its valid in java. this is called implicit up casting (JVM casts sub type to super type object) where reference of super type can refer to sub type but with super type reference you can only get access to only those variables and methods which are declared/defined in super type.

Upvotes: 0

Chowdappa
Chowdappa

Reputation: 1620

It's valid. As per Java's fundamental rule "Super class reference (A a) can refer sub class object (b= new B())".

Upvotes: 0

Varun Tulsian
Varun Tulsian

Reputation: 113

Yes this is a valid java assignment statement.

A a = (A) new B();

In java a child object can be referenced from the parent class.

Upvotes: 0

SpringLearner
SpringLearner

Reputation: 13854

Yes this is valid in java

abstract class A {...}

class B extends A {...}

A a = new B();

Upvotes: 0

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