Review of Terminology

• 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

These are terms taught in Programming I and Programming IIThis list provides a list of terms to review

Review of Java Constructions

• 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)

More Review from Programming I and Programming II

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

Exceptions

• 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

Abnormal conditions arising while a program executes

Example with an Exceptionpublic 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;}

Java Exception Handling

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 AdvantageSeparates the error handling from the main flow of logic

Handle where it occurs

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;

}

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 */ }

Example Java Exceptions

• ArithmeticException• ArrayIndexOutOfBoundsException• FileNotFoundException• IllegalArgumentException• IOException• NoSuchElementException• NullPointerException• NumberFormatException• StringIndexOutOfBoundsException• TypeMismatchException

There are many others

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.

Exception Hierarchy

• Object• Throwable• Exception• RunTimeException• The various exceptions• Notes

– NumberFormatException descends from IllegalArgumentException

– ArrayIndexOutOfBoundsException and StringIndexOutOfBoundsException descends from IndexOutOfBoundsException

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

Streams

• 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);

Flow of data from source to sink

Input and Handle Exceptions

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); }} }

System.out.println( readDouble(5,10) );

Input with Scanner Classdouble 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) { scan.next(); System.out.println("Must be >="+min+" and

<="+max); }} }

• Other Scanner methods– nextByte(), nextFloat(), nextLong(), nextInt(), nextBoolean(),

nextLine()

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

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());

Keyboard.java

• 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

A Java class using of exceptions and wrappers

Pseudo Code

• 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

A principle way of describing computer algorithms

Examples to follow

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))

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