Interface: Interface is a reference type in Java, which contains a collection of abstract methods. An interface needs to the follow certain conditions such as: One cannot instantiate an interface. Interfaces do not contain any constructors. All methods present in the interface are abstracts. An interface does not contain any instance field. An interface cannot be extended by a class. Comparable Interface : A comparable interface is a generic interface that defines the compareTo() method that is used for comparing objects. Using comparable interface, one can choose the properties of the objects, rather than the reference location of the objects. Example: //java langauage package for comaprable interface package java.lang //comparable interface definition public interface Comparable <E> { //use of compareTo to compare objects public integer compareTo(E o); } Explanation: The compareTo() method determines the order of this object with the specified object “o” and returns a negative integer, zero or positive integer, if this object is less than, equal to or greater than object “o”.

Question

Given a Student class, and UndergradCourse is a true subtype of Course, there is one method called recommend in the Student class: public class Student { public Course recommend(Course pCourseID); } Please evaluate if EACH of the method in UndergradStudent class violates the Liskov Substitution Principle. public class UndergradStudent extends Student { 1. public Course recommend(UndergradCourse pCourseID); 2. public UndergradCourse recommend(Course pCourseID); 3. public UndergradCourse recommend(Object pCourseID); 4. public Course recommend(Course pCourseID) throw SomeCheckedException;

Answer 1

Question

Chapter 13.6, Problem 13.6.1CP

Program Plan Intro

Interface:

Interface is a reference type in Java, which contains a collection of abstract methods.

An interface needs to the follow certain conditions such as:

One cannot instantiate an interface.

Interfaces do not contain any constructors.

All methods present in the interface are abstracts.

An interface does not contain any instance field.

An interface cannot be extended by a class.

Comparable Interface:

A comparable interface is a generic interface that defines the compareTo() method that is used for comparing objects.

Using comparable interface, one can choose the properties of the objects, rather than the reference location of the objects.

Example:

//java langauage package for comaprable interface

package java.lang

//comparable interface definition

public interface Comparable <E>

{

//use of compareTo to compare objects

public integer compareTo(E o);

}

Explanation:

The compareTo() method determines the order of this object with the specified object “o” and returns a negative integer, zero or positive integer, if this object is less than, equal to or greater than object “o”.

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