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Questions theory




Create a Word document containing the answers to all the problems given below.;What is an abstract class and how does it differ from a regular class?;Why are abstract class constructors defined as protected?;Class X defines method M1() as abstract. Class Y inherits from Class X and implements the method M1(). Given the following code, explain why a reference to the abstract class X is allowed to refer to an object of the concrete class Y. Explain what happens when the reference to the abstract class X is used to execute method M1().;X obj = new Y();obj.M1();What are interfaces allowed to contain?;Define a simple interface named Motorized with one method (maxSpeed) which returns the maximum attainable speed and another method (fuelType) which returns the type of fuel required.;Given the interface defined in question 5, if a class named Motorcycle implements this interface, explain why the following code is legal. What happens when the interface reference vehicle invokes the maxSpeed method?;Motorized vehicle = new Motorcycle();System.out.print(?The max speed is %d\n?, vehicle.maxSpeed());What is an event object? Give an example.;What is an event source? Give an example.;What is an event listener? Give an example.;What is a nested inner class? What special privileges does a nested inner class have? Give an example of how you declare a nested inner class.;You are writing a simple GUI application using a class called MyGuiClass. Your GUI will have a JButton which your program will need to respond to when it is clicked. Describe what you would need to do to setup event handling using a nested inner class. Use Java code fragments in your answer.;If the GUI in the above example had three JButtons, how would you change your actionPerformed method to handle events from the three different buttons?;Here are some class definitions with questions that follow.;interface MyInterface;// Methods of MyInterface;public SomeClass implements MyInterface;// All methods of SomeClass and MyInterface;SomeClass obj = new SomeClass();a. MyInterface miobj = obj;b. SomeClass obj2 = miobj;c. miobj.aMethodOfSomeClass();A. Is statement a above legal, or is casting required? Explain.;B. Statement b is trying to assign the SomeClass object refered to by miobj to a SomeClass reference variable obj2. What is wrong with this statement and how would you fix it.;C. In statement c, an interface reference is trying to access a SomeClass class method that is not part of MyInterface. Is this legal? Explain.


Paper#67876 | Written in 18-Jul-2015

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