Review of Terminology

1. Review of Terminology These are terms taught in Programming I and Programming II This list provides a list of terms to review • Variable, Constant, Identifier, Reserved word, Scope, Case sensitive • Operator, Precedence, Cast • Array, Vector • Primitive data, Object, Reference, Alias • Class, Object, Inheritance, Polymorphism • Assignment, Widening, Narrowing • Constructor, Destructor, Garbage collection • Static method, Static variable, Instance variable • Private, Public, Protected • Method signature, Overloading, Formal, Actual, this, super • String, Concatenation, Escape sequence, white space • Byte code, Applet, Compiler, Interpreter • Pre-test, Post-test, Counter controlled • Boolean, Block statement, condition

2. Review of Java Constructions More Review from Programming I and Programming II • Using the Java Class Library • E.g.: Random, StringTokenizer, System, DecimalFormat, Math • Operators (++,--,+,-,*,==,=,%,?,+=,*=, etc.) • Primitive data types versus reference objects • String compare, initialization, and concatenation. • Aliases, null pointers, dangling references, equals, compareTo • Control constructs • if (<exp>) <statement> [else <statement>] • while (<exp>) <statement> • do <statement> while (<exp>); • for (<exp>; <exp>; <exp>) <statement> • Methods: parameter passing, signature line. • Declaring arrays, vectors, ArrayList, Initialization list • Classes: Inheritance (extends), Polymorphism (interface, abstract) • Input and output • Built in interfaces (Comparable, Iterator)

3. Good Programming Conventions • Syntactical conventions • When and how much to indent • Reasonable identifier names • Single purpose methods without side-effects and reasonable size • Limit the scope of variables • Define class variables as high in the hierarchy as possible • Common programming pitfalls • Comparing objects without equals() and compareTo() • Exceeding maximum numbers • Implicit type conversions (System.out.println(“ “+3+2);) • Debugging techniques • Be structured, change one thing at a time • Don’t make changes without being sure why • Utilize available debugging tools (breakpoints, watch, step, prints) • Make use of assertion type statements

4. Exceptions Abnormal conditions arising while a program executes • How do programs handle exception? • Java try/catch exception handling • Where should a program handle it? • Nowhere: program aborts • At point where exception occurs • Pass it up to a calling method (punt) • Examples • Divide by zero • Decimal when integer expected • Trying to use a file that doesn't exist

5. public double avg(int n) { int sum = 0; for (int k=1; k<=n; k++) sum += k; return sum / n; } // Question: What happens if n is zero? public double avg(int n) { int sum = 0; if (n==0) { return 0; } for (int k=1; k<=n; k++) sum += k; return sum / n; } Example with an Exception

6. Java Exception Handling Handle where it occurs public double avg(int n) { int sum = 0; try { for (int k=1; k<=n; k++) sum += k; return sum / n; } catch (Exception e) { return 0; } } Exception Handling Advantage Separates the error handling from the main flow of logic

7. Punt Exception to Calling Method public double avg(int n) throws ArithmeticException { int sum = 0; for (int k=1; k<=n; k++) sum += k; return sum / n; }

8. Syntax try { // Attempt to execute these statements } catch (ExceptionName1 en1) {/* handling code */ } catch (ExceptionName2 en2) {/* handling code */ }... catch (ExceptionNamek enk) {// handling code } finally { /* this code always executes */ }

9. Example Java Exceptions There are many others • ArithmeticException • ArrayIndexOutOfBoundsException • FileNotFoundException • IllegalArgumentException • IOException • NoSuchElementException • NullPointerException • NumberFormatException • StringIndexOutOfBoundsException • TypeMismatchException

10. Creating your own Exceptions public class MyException extends Exception { public MyException() { super("MyException"); // Special exception handling logic } } Sometimes Java doesn't have a suitable exception for your purposes. You can create your own.

11. Exception Hierarchy • Object • Throwable • Exception • RunTimeException • The various exceptions • Notes • NumberFormatException descends from IllegalArgumentException • ArrayIndexOutOfBoundsException and StringIndexOutOfBoundsException descends from IndexOutOfBoundsException

12. Which Exceptions are Thrown? • Integer.parseInt("26.2"); • String s; s.indexOf('a'); • String s = "hello"; s.charAt(5); • String s[] = new String[5]; s[5] = "hello"; • StringTokenizer t = new StringTokenizer(""); System.out.println(t.nextToken()); • Int x = 0; int y=3; System.out.println(y/x); How could you recover from an ArrayIndexOutOfBoundsException? Try Exercise: 10.9, 10.10, and 10.11 in the Text

13. Streams Flow of data from source to sink • Wrappers • Class adding functionality to another class or primitive type • Examples: BufferedReader, Integer • Built-in streams (System.in, System.out, System.err) • Categories • Character vs. byte, • Process vs. data (to filter) • Receive vs. send • Example: InputStreamReader isr = new InputStreamReader(System.in);BufferedReader in = new BufferedReader(isr);

14. Input and Handle Exceptions System.out.println( readDouble(5,10) ); double readDouble(double min, double max) { InputStreamReader isr=new InputStreamReader(System.in); BufferedReader in = new BufferedReader(isr); double value; while (true) { try { System.out.print("Enter a Double: "); value = Double.parseDouble(in.readLine()); if (value>=min && value<=max) return value; throw new NumberFormatException(); } catch (Exception ex) { System.out.println("Must be >="+min+" and <="+max); } } }

15. Input with Scanner Class double readDouble(double min, double max) { Scanner scan = new Scanner (System.in);double value; while (true) { try { System.out.print("Enter a Double: "); value = scan.nextDouble(); if (value>=min && value<=max) return value; throw new NumberFormatException(); } catch (Exception ex) { System.out.println("Must be >="+min+" and <="+max); } } } • Other Scanner methods • nextByte(), nextFloat(), nextLong(), nextInt(), nextBoolean(), nextLine()

16. Example: What Prints? int value = 0; Scanner scan = new Scanner(System.in); for (int i=0; i<=4; i++) { try { value = scan.nextInt(); if (value%3==2) throw new NumberFormatException(); if (value>=1 && value<=3) throw new IndexOutOfBoundsException(); value += 2; } catch (InputMismatchException ex) { value += 1; } catch (NumberFormatException ex) { value += 2; } catch (IndexOutOfBoundsException ex) { value += 3; } finally { value += 4; } System.out.println(value); scan.nextLine(); } Assume: user respectively types 0, abc, 2, 3, and 4 as input. Recall: ‘%’ calculates remainder (i.e. 5%3 calculates 2). Answer: 6, 11, 8, 10, 10

17. String Tokenizer Class • Token: A group of characters treated as a unit. • StringTokenizer objects break a string into a set of tokens • Constructors • StringTokenizer(String s) • StringTokenizer(String s, String dilims) • StringTokenizer(String s, String dilims, boolean b) • Methods • hasMoreTokens(), nextToken() • Example: • String str = “300 + 4.2i”.replaceAll(“\\s+” , “”); // eliminate white space • StringTokenizer tokens = new StringTokenizer(str, "i+-",true); • System.out.println(tokens.nextToken()); • System.out.println(tokens.nextToken()); • System.out.println(tokens.nextToken()); • System.out.println(tokens.nextToken()); • System.out.println(tokens.hasMoreTokens());

18. Keyboard.java A Java class using of exceptions and wrappers • We will use Keyboard.java in lab 2 • The source is posted on our class web site • It provides general purpose keyboard input methods • It provides example code for • Exception Handling • Practical use of the StringTokenizer class • Instantiation of a character stream for keyboard input • Uses data conversion methods • Provides “type ahead” input • Uses wrapper classes

19. Pseudo Code A principle way of describing computer algorithms • Acceptable Pseudo code must: • Enough detail so a competent programmer could implement the algorithm • Not so much detail that it would be easier to just look at the code • Conventions • It should be language independent • Bold keywords such as: IF, WHILE, DO, etc. • Italicize variables • Use English like statements Examples to follow

20. Lab 1 Complex Number Calculator • Adding complex numbers • Add real to real, and imaginary to imaginary • Ex: 1+2i + 3+4i = (1+3) + (2+4)i = 4 + 6i • Subtracting complex numbers • Negate signs and do an addition • Ex: 1+2i – (3+4i) = (1-3) + (2-4)i = -2 -2i • Multiply complex numbers • Real part = real1 * real2 – imaginary1 * imaginary2 • Imaginary part = real1*imaginary2 + imaginary1*real2 • Ex: (1+2i)*(3+4i) = (1*3-2*4) + (1*4 + 2*3)i = -5 + 10i • Divide complex numbers • Multiply top and bottom by conjugate of denominator • Conjugate flips sign of imaginary part. Conjugate of 3+4i = 3-4i. • Ex: (1+2i)/(3+4i) = (1+2i)(3-4i) / ((3+4i)/(3-4i))

21. Initial Lab Assignment Goals • Become proficient with the StringTokenizer class • Implement a program requiring some tricky logic • Understand and use a parse tree in design • A parse tree draws the paths through an algorithm as a diagram • We will illustrate this in class • Practice describing program logic in pseudo code • Become familiar with exception handling in of Java • Perform I/O handling Exceptions appropriately Note: http://java.sun.com/javase/reference/api.jsp is a good place for Java help