CIS 120 Notes

True-False Guide

Answers to some True-False questions from the old final exams

T F

T - When you override the equals method of a class, you should be sure to override the hashCode method compatibly.
F - If A is a subtype of B, then Set<A> is a subtype of Set<B>.
T - When using the Java IO libraries, one should generally wrap a FileReader object inside a BufferedReader to prevent significant performance problems.
F - It is possible to create an object of type Set<int>.
F - An object's static type is always a subtype of its dynamic type.
F - The value null can be assigned to a variable of any type.
T - A method with the following declaration definitely will not throw an IOException to a calling context.

public void m() {...}

T - The @Override annotation prevents accidental overloading of a method.
F - In some cases, dynamic dispatch of a method invocation requires the Java ASM to search the entire stack to find the appropriate code to run next.
F - It is not possible to call a method declared as static from within a non-static method.

T - The type MyPanel is a subtype of Object.
F - The new object created on line 27 is an instance of MyPanel (SP15 - Appendix D).
T - The instance variables x and y on lines 23 and 24 can only be modified by methods of the MyPanel class or the methods of any inner classes of MyPanel.
T - The dynamic class of f (declared on line 13) is JFrame.
T - The mouseMoved method on line 28 is called by the Swing event loop in reaction to the user moving the mouse in the main window of the application.
F - The paintComponent method on line 42 is only invoked once, at the start of the application.
F - A JPanel cannot be added to another JPanel using the add method.
F - If the user replaces the code on line 31 (the call to repaint()) with paintComponent (new Graphics ()), then the behavior of the application would not change.
T - The anonymous class defined on line 27 implements or inherits all members of the MouseMotionListener interface.
F - The method createAndShowGUI cannot be invoked without an instance of class GUI.