Can abstract class have protected members?
Abstract classes are similar to interfaces. You cannot instantiate them, and they may contain a mix of methods declared with or without an implementation. However, with abstract classes, you can declare fields that are not static and final, and define public, protected, and private concrete methods.
Can abstract class have methods in Java?
An abstract class can have a data member, abstract method, method body (non-abstract method), constructor, and even main() method.
Should abstract methods be public or protected?
Abstract methods are declaration only and it will not have implementation. A Java class containing an abstract class must be declared as abstract class. An abstract method can only set a visibility modifier, one of public or protected. That is, an abstract method cannot add static or final modifier to the declaration.
Is it necessary to override all methods of abstract class in Java?
An abstract method has no implementation. Subclasses of an abstract class must implement (override) all abstract methods of its abstract superclass. The non-abstract methods of the superclass are just inherited as they are. They can also be overridden, if needed.
Why can’t abstract methods be private?
Private methods are not polymorphic (you cannot inherit them), so it makes no sense to make a private method abstract. Making a method abstract means you’d have to override and implement it in a subclass, but since you can’t override private methods, you can’t make them abstract either.
What happens if you don’t override a method?
Put differently: If you don’t override equals any two objects will be considered non-equal. Since Object. hashCode ensures that all objects are distributed as evenly as possible in a hash based collection Object. hashCode is optimal, and overriding it with anything else will worsen the performance.
How to test protected methods of abstract class?
Of course if implementation to test is abstract, you have to create normal subclass of class under test by yourself (or do it via some mocking library if fits better for your purposes). Also in such a case, no need to create layer of public methods for just for calling protected visibility methods.
What do you need to know about abstract classes in Java?
You expect that classes that extend your abstract class have many common methods or fields, or require access modifiers other than public (such as protected and private). You want to declare non-static or non-final fields. This enables you to define methods that can access and modify the state of the object to which they belong.
When do abstract methods need to be declared?
When an abstract class is subclassed, the subclass usually provides implementations for all of the abstract methods in its parent class. However, if it does not, then the subclass must also be declared abstract.
How are abstract classes similar to an interface?
Abstract classes are similar to interfaces. You cannot instantiate them, and they may contain a mix of methods declared with or without an implementation. However, with abstract classes, you can declare fields that are not static and final, and define public, protected, and private concrete methods.
