Introduction to Java Programming by Laurie Murphy Revised 09/08/2016

What is Java? What does a Java program look like? How do I go about writing a Java program?

What is Java?

Java is an object-oriented programming language developed at Sun Microsystems in 1995.

Algorithm Program

Automobile C02 Calculator Ask the user for miles per gallon Ask the user for the number of miles driven Calculate the gallons of fuel used Calculate pounds of CO2 used (gallons of fuel used times the emissions factor of 19.6) Display gallons of fuel and CO2 used algorithm

CPU: Central Processing Unit The “brain” of the computer. Types: –Intel: Core i5, Core i7, Pentium, Core Duo, … –AMD: Bulldozer, Athlon, Opteron, … –Motorola: 68000, PowerPC,… –ARM: ARM11, Cortex, ARM3,… CPUs (Processors) may speak different languages.

The CPU Understands only one language

What does a Java program look like?

// calculates pounds of C02 emitted by a gasoline powered automobile public class CO2Calculator { public static void main(String[] args) { int milesDriven = 360; double mpg = 24.5; double gallonsUsed, co2Used; double emissionsFactor = 19.6; // calculate gallons of fuel used gallonsUsed = milesDriven/mpg; // calculate and display pounds of C02 emitted co2Used = gallonsUsed * emissionsFactor; System.out.println("You used " + co2Used + " pounds of C02”); }

ClassA methodOne methodTwo statement1 statement2 statement3 program structure ClassB

public class C02Calculator {}{} // comments about the class class header class body Java code

public class C02Calculator {}{} public static void main (String[] args) {}{} // comments about the class // comments about the method method header method body Java code

public class C02Calculator {}{} public static void main (String[] args) {}{} Reserved words

Java reserved words abstract boolean break byte case catch char class const continue default do double else extends false final finally float for goto if implements import instanceof int interface long native new null package private protected public return short static strictfp super switch synchronized this throw throws transient true try void volatile while

public class C02Calculator {}{} public static void main (String[] args) {}{} Identifiers

Rules for Identifiers An identifier can be made up of letters, digits, the underscore character ( _ ), and the dollar sign ( $ ) Identifiers cannot begin with a digit Java is case sensitive - Total, total, and TOTAL are different identifiers By convention, Java programmers use different case styles for different types of identifiers, such as –title case for class names - Lincoln –upper case for constants - MAXIMUM

Identifying identifiers: is it valid or not? class CLASS 1time abc123 bank-account bank_account $hello

Variables 0x000 0x001 0x002 0x003 0x004 0x005 0x006 0x007 int milesDriven = 360; 360 variable milesDriven is a symbolic name for the memory location 0x003. memoryJava code

How do I go about writing a program?

compile execute edit

Program Development Process Text editor Source code (.java ) Saves Java statements

Text Editor: Atom

Program Development Process Text editor Source code (.java ) Java compiler Is read by Byte code (.class ) Produces

Java Compiler: javac

Program Development Process Text editor Source code (.java ) Java compiler Byte code (.class ) Java Virtual Machine Is interpreted by Program Execution Results in

Java Interpreter: java

compilation/syntax errors

logic errors

Let’s give it a try…