Answers to Questions and Exercises: Interfaces

Questions

Question 1: What methods would a class that implements the java.lang.CharSequence interface have to implement?
Answer 1: charAt, length, subSequence, and toString.

Question 2: What is wrong with the following interface?

public interface SomethingIsWrong {
    void aMethod(int aValue) {
        System.out.println("Hi Mom");
    }
}

Question 3: Fix the interface in Question 2.
Answer 3:

public interface SomethingIsWrong {
    void aMethod(int aValue);
}

Question 4: Is the following interface valid?

public interface Marker {
}

Exercises

Exercise 1: Write a class that implements the CharSequence interface found in the java.lang package. Your implementation should return the string backwards. Select one of the sentences from this book to use as the data. Write a small main method to test your class; make sure to call all four methods.
Answer 1: See CharSequenceDemo.java

Exercise 2: Suppose that you have written a time server, which periodically notifies its clients of the current date and time. Write an interface that the server could use to enforce a particular protocol on its clients.
Answer 2: See TimeClient.java.