Helsingin yliopisto / Tietojenkäsittelytieteen laitos / 581258-1 Johdatus ohjelmointiin
Copyright © 1998 Arto Wikla. The use of this material is only allowed for studying purposes of private persons. Any other use of this material, such as commercial or other courses, is forbidden.

581258-1 Introduction to Programming: 2. exam 17.12.1998/AW

Write on top of every answering paper the name of the course, the date of the examination, your name, your date of birth and your signature.

You are allowed to use the tools of the class Read (in Finnish Lue) when writing your programs.

1. Explain the following concepts shortly and precisely:

   primitive type
   reference type
   overloading
   overriding
   package
                                                              (5 points)

2. In a game play each player has a name, the description of his/her role in the game, his/her goodness as an integer -10...10, and his/her strength as a decimal value 0.0...1.0. The weight of a player in "defending the good" is calculeted with formula goodness * strength

   • a) Model players as a class Player.

   • b) Program a method public static void sort that gets an array of players as parameter and then sorts the array to descending order according to player's weight in "defending the good".

   • c) Program a parameterless method public static Player readPlayer that asks the data of a player from the user, and then returns the corresponding Player object.

   • d) Program an application, which by using these methods, reads the data of the players, and then prints all the players in the order given by the sorting method of point b. Those methods are included in a class of their own, not to the class of the application. Decide by yourself, how the program finds out the number of players

                                                             (8 points)

3. One of your friends, taking part to this course, has not totally understood the idea of "classes" and "objects". He/she hasn't even got the idea, why he/she should understand these concepts. Help your friend and write him/her an explanation of the matter. Remember that good examples are important in learning. Your explanation will be evaluated from the point of view of your friend. So do not write to your teacher, he/she already knows it!

                                                              (5 points)

4. You are given a class called InpFile for reading input files. The class has a constructor:

• InpFile(String name) creates an InpFile object from where you can read the lines of a file. The parameter is the name of the file. If no file is found, the read-method will return null values. So, empty and missing files will look similar to the user. In this case you don't need to take care of any errors ("exceptions") in file handling.

The class has a method for reading lines:

• String read() returns next line from the input file. When the file ends (or doesn't exist at all!) the method will return the value null.

By using this class, write a program that asks the user for the name of the input file, a character to be replaced (oldChar), and a replacing string (newString). Then the program prints the file on the screen, modified so that all oldChar characters are replaced by the string newString.

                                                              (8 points)