What goes in an abstract for a dissertation?

The abstract is a summary of the whole thesis. It presents all the major elements of your work in a highly condensed form. An abstract often functions, together with the thesis title, as a stand-alone text. Abstracts appear, absent the full text of the thesis, in bibliographic indexes such as PsycInfo.

Can abstract class have body?

Abstract methods cannot have a body; all they can have is a method signature as shown in the example above. Variables are not allowed in interface. Hence any data declaration is ‘ public static final ‘; hence only constants. Interfaces can extend other interfaces ( one or more ) but not classes ( abstract or not ).

Why can’t we instantiate an abstract class?

Because an abstract class is an incomplete class (incomplete in the sense it contains abstract methods without body and output) we cannot create an instance or object; the same way you say for an interface. You CAN instantiate an abstract class. You only need to provide a concrete subclass.