581325-0 Programming in Java, exam 15 December 2000/AW

Write the name of the course, the date of the exam, your name, personal number and your signature at the top of each paper. Write each answer on a separate paper!

Questions 2 and 3 differ from the Finnish version, because of using different text books!

You have at your disposal the class Puddingbasin, which implements the general features of a puddingbasin. The class has only one constructor:
- Puddingbasin(double bowlsize), the parameter is the size of one bowl of pudding. Note! his constructor does not check the parameter, it must be checked before calling the constructor.
The class has the accessors:
- public void addMaterial(double amount) adds the parameter's worth of pudding material to the basin. If the value of the parameter is not correct, the method is able to handle it sensibly.
- public double givePudding(): If there is at least one bowl of pudding in the basin, the method removes one bowl and returns the size of the bowl. If there was not enough pudding in the basin for one bowl, the method returns the whole contents of the basin, which then becomes empty.
- ... (There may be other methods in the class, but we do not know about them.)
Implement the class ChristmasPuddingbasin as a subclass of the class Puddingbasin. The class ChristmasPuddingbasin has one constructor:
- ChristmasPuddingbasin(double bowl), give the size of one bowl of Christmas pudding as parameter.
The class ChristmasPuddingbasin has its own accessors:
- public void addRaisins(int amount) adds raisins to the pudding. A negative amount subtracts raisins. Of course, there may be only zero or more raisins in the basin.
- public double givePudding() works like the method givePudding() in the superclass, except that the method returns the size of the bowl as a negative if the bowl does not contain raisins, if the value is positive, it means that one raisin was removed from the basin. Whether a raisin ends up in a bowl is determined (unrealistically) as follows: if there are raisins in the basin, and at least a small amount of pudding can be given, one raisin will follow along with the probability of 0.2 (if (Math.random()<0.2)...)). One bowl may contain one raisin at the most.
Note! The class Puddingbasin is at your disposal, you do not need to program it!
```
                                                            (17 pistettä)
```
- Explain the following concepts shortly and precisely:
- One of your friends has not fully understood the ideas of "classes", "objects" and "inheritance" 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!
```
                                                            (19 points)
```
You are given a class InpFile for reading input files. The class has a constructor InpFile(String name). The parameter is the name of the file.
The lines are read wit the method
```
   public String read()
```
When the file ends, the method returns the value null.
The class takes care of all the possible exeptions. When an error occurs, the class gives an error message and exits the program.
By using this class, write a program AreTheFilesSimiliar for comparing two files. The names of the files are given to the program as command-line arguments. The program compares the two files line by line, and prints all different lines to the screen. An example of the output:
```
1>cat is walking<
2>rat is walking<
1>1235123<
2>1234123<
1>abc<
2>abc  <
2>  the second<
2>was  <
2>longer!<
```
Thus the lines differing from each other are printed between either characters "1>" and "<" or "2>" and "<", depending on where the line in question comes from: from the first file or from the second file. If either file ends before the other, the extra lines of the longer file are printed. The program does not print anything else.
In the example above the files had three different lines and the second file seems to have been three lines longer than the first.
The program doesn't have to take care of the exceptions, the class InpFile takes care of them.
```
                                                            (17 points)
```

Good Luck & Merry Christmas!