10/8/2018 Programming Data Structures. class diagram for assignment 08 review: polymorphism review: exception new: File I/O

Transcription

1 10/8/2018 Programming Data Structures class diagram for assignment 08 review: polymorphism review: exception new: File I/O 1

2 class diagram (informal) link the parent classes and child classes describe the instance variables of each class (with different accesses: private, protected, package, public) first, list private instance variables then, list protected instance variables finally, list public/package instance variables describe the methods of each classes (with different accesses: private, protected, package, public) first, list private methods then, list protected methods finally, list public/package methods 2

3 class diagram example of assignment 07- solution 3

4 Review: Polymorphism Quiz question examples A derived class is also called a: a. sub class b. super class c. base class d. all of the above 4

5 Review: Polymorphism Quiz question examples The keyword extends indicates: a. encapsulation b. polymorphism c. inheritance d. none of the above 5

6 Review: Polymorphism Quiz question examples refers to the ability to associate many meanings to one method name by means of the late binding mechanism. a. Inheritance b. Encapsulation c. Polymorphism d. None of the above 6

7 Review: Polymorphism Quiz question examples binding refers to the method definition being associated with the method invocation when the code is compile. a. Dynamic b. Late c. Early d. None of the above 7

8 Review: Polymorphism Quiz question examples Java does not use late binding for methods marked as: a. final b. static c. private d. all of the above 8

9 Review: Exception Quiz question examples Try blocks contain code that could possibly: a. handle an exception b. throw an exception c. catch an exception d. display an exception 9

10 Review: Exception Quiz question examples A block should immediately follow a try block. a. try b. catch c. fail d. final 10

11 Review: Exception Quiz question examples If a method does not catch an exception, then it must at least warn programmers/compiler that any invocation of the method may possibly throw an exception. This warning is called a/an: a. Exception handler b. Throws a clause c. Try block d. Catch block 11

12 Intro to File I/O To read a file, we use FileInputStream and Scanner import java.io.fileinputstream; import java.util.scanner; String filename = FileName ; FileInputStream inputstream = new FileInputStream(filename); Scanner inputscanner = new Scanner(inputStream); String line1 = inputscanner.nextline(); inputscanner.close(); 12

13 Intro to File I/O To write a file, we use FileOutputStream and PrintWriter. import java.io.fileoutputstream; import java.io.printwriter; String filename = FileName ; FileOutputStream fileoutputstream = new FileOutputStream(filename); PrintWriter writer = new PrintWriter(fileOutputStream); writer.println( aaaaaaaaaaaaabbbbbbbbbbbbbcccccccccccccc ); writer.close(); 13

14 In-class assignment 1 st part (1 point) Draw your class diagram for assignment on paper (submit it to me, or drop it off in my office) 2. submit a Word or Pdf to Github repository 3. (no, you don t need to submit your thoughts) think about how the instance variables and the methods will help you achieve the requirements described in assignment 08 14

15 In-class assignment 2 nd part (1 point) 1. create a Main class with the main method: public static void main(string[] argv) 2. Inside the main method, use the methods in slides to read the file readme.txt (can be downloaded from Github), and then, write the third line of readme.txt to a new file called writeme.txt. 3. Suppose before every time the main method is called, there is no writeme.txt in the current directory Hint: you will need to use try/catch, otherwise, there will be a compiler error. GitHub link: 15

16 Debug Case: what does this bug say? java.io.filenotfoundexception: readme.txt (The system cannot find the file specified) at java.io.fileinputstream.open0(native Method) at java.io.fileinputstream.open(fileinputstream.java:195) at java.io.fileinputstream.<init>(fileinputstream.java:138) at java.io.fileinputstream.<init>(fileinputstream.java:93) at Main.main(Main.java:12) 16