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Introduction to Programming

Lecturer: Steve Maybank

Department of Computer Science and Information Systems

sjmaybank@dcs.bbk.ac.ukSpring 2013

Week 1: First Program

Module Information

Time: 18.00-21.00 on Fridays in the spring term.

A-K: lectures 18.00 to 19.20 lab sessions 19.40 to 21.00 L-Z: lab sessions 18.00 to 19.20 lectures 19.40 to 21.00 Week 11: in lab test.

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Assessment

In Lab test: 30% Two hour examination in summer

2013: 70% The mock examination and the

mock in Lab test do not contribute to the marks.

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Essential Text Book

Cay Horstmann (2013) Java for Everyone, Wiley, 2nd edition.

This module draws on the first six chapters of JFE.

The lab classes are based on exercises suggested in JFE.

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Syllabus First program Safe operation of computing equipment Variables and number types String types Arithmetic and Boolean operations If statement Loops Methods Arrays

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This Lecture

Based on Ch. 1 of JFE Aim 1: provide background

information on computing Aim 2: provide enough information

to write a first Java program.

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Structure of a Computer

Central Processing Unit: executes instructions. Main memory (= primary storage): stores

programs and data ready for the CPU. Bus: connects the CPU and the main memory.

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CPUMainmemory

Problem

The CPU of a computer is designed to carry out a fixed set of simple instructions.

It takes too much time to write programs using these instructions.

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Solution

Write programs in a special high level programming language.

Then use another program (a compiler) to convert each high level program into a list of instructions for the CPU.

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Java

First version developed in 1991 by James Gosling and Patrick Naughton for use in consumer products, eg. set top boxes.

Java based browser presented in 1995 at the SunWorld exhibition.

A browser can run Java code (applets) obtained from anywhere on the Internet.

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Advantages of Java

Portable: the same Java program can be run without change on Windows, UNIX, Linux or Macintosh.

Safe: a browser can run a Java program without endangering the PC running the browser.

Very large libraries for graphics, user interface, cryptography, networking, etc.

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Java Portability The Java compiler converts a Java

program to Java byte code. The Java byte code is executed by a

Java Virtual Machine. The JVM is not portable: different

JVMs are needed for different platforms.

The Java program is portable given the right JVM.

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Integrated Development Environment

The IDE for Java is BlueJ BlueJ facilities for Java programs:

EditCompileRun

See practical session.

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BlueJ Console Window

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See http://en.wikipedia.org/wiki/File:BlueJ_screenshot.png

Classes, Objects and Methods

A class describes a set of objects with the same behaviour.

An object consists of data, together with methods which act on the data in that object.

A method is a sequence of instructions with a name.

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The String Class Objects (string literals): “Hello”,

“World”. Methods: the object “Hello” contains

methods length() and substring() which act on the data in “Hello”:

“Hello”.length(); // 5“Hello”.substring(0, 2); // “He”

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Java Programs

Java programs consist of classes. When a Java program runs, objects

are created and the methods act on the data in the objects.

Exception: a static method can be used without any associated object.

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My First Program

public class HelloPrinter{

public static void main(String[] args){

System.out.println(“Hello, World!”);}

}

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Commentary 1

MFP contains a single class: HelloPrinter

The class has no associated objects. The class contains one method,

main(), which can be invoked without first creating any object.

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Commentary 2 public class: HelloPrinter and main()

are available to any user static: main() can be invoked

without any associated object. void: no value is returned by

main(). public, class, static, void are

reserved words.

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System.out.println(“Hello”) System.out is an object println() is a method which is

applied to data in System.out. The string “Hello” is a parameter

for the method println(). Note how the details of System.out

are hidden from the user. This is an example of encapsulation.

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Java Syntax Braces (brackets) occur in matching pairs,

{…}. Every statement must end in a semicolon. Upper case and lower case are distinguished. Every Java application must have a main

method. Reserved words cannot be used for other

purposes. A method can have any number of

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String Concatenation “Hello, ”+”World!” produces

“Hello, World!” “Hello”+7 produces

“Hello7”(The number 7 is converted to a string.)

Similarly, 7+”Hello” produces “7Hello” 7+7 produces 14.

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Escape Sequences On printing “He said \”Hello\”” the result is

He said “Hello”The pair \” is an escape sequence.

The escape sequence \n denotes new line, for example

System.out.print(“*\n**\n”);produces***

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