1DV506, Problem Solving and Programming, Autumn 2018

Assignment 4: Exceptions, IO, and Interfaces

Problems?
Do not hesitate to ask your teaching assistants at the practical meetings (or Jonas/Lars at the lectures) if you have any problems. You can also post a question in the assignment forum in Moodle.

Prepare Eclipse for Assignment 4

Lecture 9 - IO and Exceptions

• Exercise 1
  Create a program Histogram.java, reading any number of integers from a file and then printing a histogram bar-chart for all integers between 1 and 100. Note: not all integers in the file are neccesarily in the interval [1-100]. An example of an execution:

  Reading integers from file: C:\Temp\integers.dat
  Number of integers in the interval [1,100]: 46
  Others: 16
  Histogram
    1  - 10  | ******
    11 - 20  | ****
    21 - 30  | **
    31 - 40  | ***
    41 - 50  | *******
    51 - 60  | ****
    61 - 70  | ***
    71 - 80  | *********
    81 - 90  | *****
    91 - 100 | ***   
         
  

  Note 1: You will have to create your own data file. We expect it to be an ordinary text file with one integer on each row. Note 2: The absolute path to the data file should be provided as an argument to the main method.
• Exercise 2
  Write a program CountChar.java, counting characters of different types in a text read from a file. Give the number of characters of the following types:
  • Upper case letters
  • Lower case letters
  • "Whitespace" (i.e. space, tab, return)
  • Other characters
  The path to the text file to read can be coded into the program. (We will test with some other file.) An example of a text file is HistoryOfProgramming. It is a part of an article from Wikipedia about the history of programming. However, we strongly recommend you to start testing your program with a smaller file where you can manually check the result.

  An execution with the file HistoryOfProgramming as input should give the following result:

  Number of upper case letters: 86
  Number of lower case letters: 3715
  Number of "whitespaces": 728
  Number of others: 152
  

  If your result does not agree completely with the example above you have to add a written explanation, why you think this happens, to your submission.

Lecture 10 - Static Members and Interfaces

• Exercise 3
  Start by creating a new sub package named stack inside your package YourLnuUserName_assign4 and save all .java files related to this exercise inside this package.
  A stack is a LiFo (Last-in, first-out) data structure with three basic operations: push, pop and peek. push is putting an element on the top of the stack, pop removes (and returns) the top element, and peek returns (without removing) the top element. Think of a stack as a pile of plates that can be found in certain restaurants. You can only add and remove the top-most plate. You can not remove any plates in the middle of the pile (without first removing all plates above it). Your task is to implement the following stack interface:

  public interface Stack {
     int size(); 			// Current stack size
     boolean isEmpty(); 		// true if stack is empty
     void push(Object element); 	// Add element at top of stack
     Object pop(); 		// Return and remove top element,
  				// exception if stack is empty
     Object peek(); 		// Return (without removing) top element,
  				// exception if stack is empty.
     Iterator<Object> iterator(); // Element iterator
  }
  
  

  The iterator traverses all elements currently in the stack, starting with the top element. Illegal operations on an empty stack (e.g., pop() and peek()) should generate an exception. You should also present a test program StackMain.java that demonstrates how each method can be used. Notice: You are not allowed to use any of the data structures in the Java library. However, you can use arrays.
• Exercise 4
  Start by creating a new subpackage named sort_cities inside your package YourLnuUserName_assign4 and save all .java files related to this exercise inside this package.
  Implement a program SortCities that reads an arbitrary number of city names and their zip codes from a text file. You can assume one city in each line and that each city name (String) and zip code (integer) is separated by a semi-colon(;). Create a class City that represents a city and create a city object for each city you read from the file. The City class should also implement the interface Comparable. Once you have read (and constructed) one City object for each line in the file you should print the cities in a sorted order based on their zip codes. An execution might look like this:

  Reading cities from file: C:\Temp\cities.dat
  Number of cities found: 7
  
  23642 Höllviken
  35243 Växjö
  51000 Jönköping
  72211 Västerås
  75242 Uppsala
  90325 Umeå
  96133 Boden
  

  Notice: We expect you to use one of the predefined sorting algorithms in the Java class library when sorting the cities.

General Java

• Exercise 5 (VG Exercise)
  The following exercise description is rather vague, more of a sketchy scenario than a concrete problem specification. Your task is to create the necessary classes to simulate this scenario. All classes should be properly documented and encapsulated.
  

  Start by creating a new sub package named newsagency inside your package YourLnuUserName_assign4 and save all .java files related to this exercise inside this package.
  Newspapers exchange news by using news agencies (such as Reuters and ITAR- TASS). A newspaper registers at a news agency and sends all its news to the agency. The news agency collects the news and broadcasts it to all registered newspapers, except from to the one who delivered it. Create the classes needed to simulate this scenario. Also create a main class to show a simulation where a couple of newpapers generate news and receive news from others.

Submission