COMP206-08S General Programming 2

Geoff Holmes and Bernhard Pfahringer

COMP206-08SGeneral

Programming 2

Department of Computer Science 2

Course Goals

First three weeks:- To learn about Java programming- To learn about data structures – in particular, learning how

to use those provided with Java (in libraries)

Second three weeks:

- To learn about Polymorphism- To learn about Java GUI programming (Swing)- To learn more about Java libraries such as FileIO and

streams


Java programming language

Developed by Sun in the early 1990s Object-oriented: programs consist of objects that

interact with each other Platform-independent: programs can run on many

operating systems Java code is translated to byte code, which is

executed by a JVM Similar to C#


Course Outline

Lectures (Mon, Wed, Fri) Labs every day – supervised 10-11 Assessment = 6 weekly assignments + 2

tests


Data Structures

A way of organizing data so that certain operations can be performed efficiently

Data structures are generic (ideally) Examples (linked lists, stacks, queues, trees, hash

tables, heaps) Many of these are implemented in Java’s

Collection Framework


IDEs Most programming languages have integrated

development environments For Java we will use Eclipse For instructions on how to set up Eclipse please

see the 203 homepage at http://www.cs.waikato.ac.nz/~eibe/COMP203A/

Note that you can use Version 5 or Version 6 of Java – the book is based on Version 5 and Version 6 is the latest.

http://www.cs.waikato.ac.nz/~eibe/COMP203A/


Java – summary of syntax

Comments One-line use:

// This is a comment Multi-line use:

/* This is a bit

longer */ Javadoc

/** Automatic documentation! */


TypesPrimitive types and constants:

byte aByte = 12; // -128 to 127short aShort = 354; // -32,768 to 32,767int anInt = 55677; // +- 2 billionlong aLong = 12345678900; // +-2 power 63float aFloat = 32.1f; // 32-bit floating point 6 sdigdouble aDouble = 26.5; // 64-bit 15 sig digitschar aChar = ‘b’; // Unicode 30,000 chars!boolean aBool = true;


Compiling Java code The command javac file.java compiles source

code and creates bytecode Source code is stored in .java files Bytecode is stored in .class files

The command java starts the Java Virtual Machine (JVM) and executes the bytecode The bytecode is translated into machine-code Most JVMs are just-in-time compilers


Useful methods When the bytecode for a .java file is executed, the

main method is called:public static void main (String[ ] args) { }

This is the starting point of a Java program To get output from your program you can write to

the standard output stream using the println methodSystem.out.println(“Hello World”);


Basic Operators Assignment operators:

+, +=, -=, *=, /= Binary arithmetic operators:

+, - , *, /, % (remainder) Unary operators:

-, ++, -- Type conversion operators:

int x = 6; int y = 10; double q = (double) x / y;


Conditional statements Equality operators:

==, != Relational operators:

<, <=, >, >= Logical operators:

&&, ||, ! The if statement

if (expression) statement

next statement


Conditionals continued The switch statement can be used when several

options are needed Break statement exits from the innermost loop or

switch statement Continue statement goes to the next iteration of

the innermost loop immediately (ie avoiding the statements of the loop)

Conditional operator testExpr ? yesExpr : noExpr


Methods Methods can be overloaded: a class can have

multiple methods with the same name (but different parameter lists)

Public methods are visible in other classes Static methods are not bound to a particular

object


Loops The for statement:

for (initialisation; test; update)statement

next statement The while statement:

while (expression)statement

next statement The do statement:

dostatement

while (expression);next statement


Methods Basic method header has a name, return type and

parameter list The method declaration includes the body Arguments are copied into the parameters: so

Java is pass by value The return statement is used to return a value to

the caller return must be present unless method is void


Reference types All types that are not primitive types are

reference types A reference variable holds the address of an

object References can be compared using == and !=

This checks whether two variables refer to exactly the same object (ie they hold the same address)

References have the value null if they do not refer to an object.


Objects

An instance of any of the non-primitive types is an object

The keyword new is used to invoke the constructor of an object

The dot operator is used to access an object via a reference variable

Objects are garbage-collected when they are no longer referenced by any variable


Arrays

Indexed from 0 The [ ] operator is used to index an array An array behaves like an object

new is used to create a new array An array variable is a reference to an array

Multi-dimensional Dynamic arrays achieved via the ArrayList


Exception handling

Handling exceptional circumstances incl errors A try block encloses code that might generate an

exception A catch block processes the exception A finally block maybe used which is always

executed Used for runtime (array bounds, null pointer etc),

checked (IO, file not found) and errors Exceptions are thrown


Strings

Objects with special properties: Immutable – cannot change once constructed Can be concatenated using +

To check equality use the equals method Many other useful methods (check the Javadoc)


I/O in Java

The java.io package contains methods for input and output

Packages are made available in your class using an import statement java.lang does not need an import statement

Java I/O is based on streams Predefined streams include System.out,

System.in and Sytem.err


Examples To read lines of input from the terminal

Create an InputStreamReader from System.in Create a BufferedReader from the

InputStreamReader Call the readLine method on the BufferedReader

To split up a line (string) into sub strings use a StringTokenizer

For file I/O you can use a FileReader and a FileWriter

COMP206-08S General Programming 2

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