1. Introduction to Java Import Scanner class to use in our program
Our program is a class, this is the header
Our program consists of 1 method, called main
Some variables (name, age, birth) and a constant
Create an input object
Prompt the user for their name and age
Compute their age and output the result
import java.util.Scanner;
public class FirstProgram {
public static void main(String[] args)
String name;
final int YEAR=2016;
int age, birth;
Scanner in = new Scanner(System.in);
System.out.print("Enter your name: ");
name = in.next();
System.out.println("Hello " + name + ", how old are you?");
age = in.nextInt();
birth = YEAR - age;
System.out.println("You were born in either " + birth +
" or " + (birth-1)); }

2. What is a Program? A program is a list of instructions
written in a programming language
that instructs the computer precisely what to do
and is written so that it is unambiguous and grammatically correct
Computers run programs
they don’t actually understand the programs, they just execute them
Computers are not capable of running programs in any language other than their native machine language
Java is not that language, therefore we have to translate every program we write into machine language
we use either a compiler or an interpreter to do this for us
programs that have syntax errors will not compile
programs that have logical errors will run but not necessarily correctly
programs may also abnormally terminate with run-time errors
In this course, we learn Java because it is popular, powerful and somewhat easy to learn – also, being an OOPL, we can learn about OOP

3. A Simple Java Program: Hello World
// a simple introductory program
public class HelloWorld {
public static void main(String[] args) {
System.out.println(“Hello World!”); }
Let’s explore the above program
The first line, starting with //, is a comment – it does nothing
The second line is our class header, always of the form public class name
later in the semester we will also learn about using the word private
The third line is the header of the main method
we will have more methods in later programs but not for now, and later in the semester we will learn what all the other stuff is in that header (void, static, String[] args)
The fourth line is our only executable statement, it outputs “Hello World!”
the { } are delimiters to indicate the start and end of blocks
the indentation and placing } on separate lines promotes readability but is not necessary

4. Anatomy of a Java Program
Import statements precede any class definition
we must import classes that we are using in our program unless those classes are built-in classes (such as System and Math)
Class header – starts a new class
Methods (early in the semester, we will only write 1 method, main)
methods consist of a header, { } and statements in { }
Inside { } we can have
variable and constant declarations
executable statements
input statements
output statements
assignment statements
calls to other methods
logic statements (selection statements, loops)
comments (comments can go anywhere we like in a program)

5. Executable Statements
These statement use reserved words and reserved punctuation marks
we must spell the reserved words correctly or else we get syntax errors
spelling includes using the right upper or lower case
Some reserved words: public, private, static, int, void, String, final, new, while, for
One type of executable statement is the assignment statement
syntax: variable = expression;
the expression can be a value, another variable, a method call, a mathematical expression, or some combination
Most executable statements end with a ;
learning when and where to use ; is a challenge but essential
Some punctuation marks we need: = + - * / % ; . ( ) { } [ ] , / \ ! < > _
see the next slide

6. Common Java Punctuation Usage

7. Block Styles We’ve seen two ways to indicate { } Which should we use?
Blocks are chunks of executable code
We place blocks inside methods and
inside certain types of executable statements
like for loops
The code in a block is placed inside { }
We’ve seen two ways to indicate { }
Which should we use?
it’s a matter of style, I prefer the one at the top of this slide but use the second one when I need to save space such as in these slides
a lot of programmers use the version on the right because its quicker and saves space if you are printing out your code
either is fine for this class

8. Why is Programming Challenging?
It is hard to express your ideas of how to do something in specific code
writing proper logic is hard
you might write code but it will not necessarily work correct
Your code will often have errors in it
syntax errors – errors with the syntax of the language
forgetting a ; or misspelling a reserved word or using the wrong data type
run-time errors – errors that arise while the program is running
asking the computer to do something it cannot do
run-time error usually cause the program to terminate, in Java there is a mechanism to keep the program running known as exception handling (we see this in CSC 360)
logical errors – errors with the logic of the program
the program may run but might or will yield wrong answers
e.g., using < instead of > or * instead of - as simple examples

9. Locate the Syntax Errors
public class AnError {
public static void main(String[] args) {
System.out.println(“Hello world); }
public class AnError2 {
public static void main(String[] foo)
System.out.println(“Hello world”);
private class AnError3 {
System.out.println(“Hello world”)

10. Java and Eclipse Java is a programming language it comes in two forms
JDK – the development kit, needed to write and compile code, we are using JDK 1.8
JRE – the run-time environment, needed to run compiled code such as in a web browser
your home computer almost certainly has the JRE but you will want to install the JDK if you do not have it, go to oracle.com
Oracle purchased Sun Microsystems who created Java, Oracle maintains it
there are many IDEs (development environments) available, we will use Eclipse because it is free and runs in Windows, Mac and Linux
go to and select the appropriate download link
if you do not have the Java JDK, install it first
when you install Eclipse, it will guess where your JDK is, and if it can’t find it you will have to specify it yourself

11. Using Eclipse Start Eclipse Select the directory for your workspace
you can set up a permanent workspace so that you aren’t asked this again
Select File  New  Java Project
specify a unique project Name and use all of the defaults, click on Finish
Make sure your new project is selected in the Package Explorer and select File  New  Class
specify a Name for the class
this Name will also be used in the filename as Name.java
it may but does not have to be the same Name as the project name
Eclipse advises you to use a different name although that is not necessary
select the checkbox for public static void main(String[] args)
later in the semester, we will use a different “method stub”
leave the rest of the defaults as is, click Finish

12. Continued Edit your program
To run your program, click on the Run button or select Run from the Run menu
by default, your program will be compiled before it is run
if you want to separately compile your program from running it, turn off “Build Automatically” (under the Project menu)
if you do so, you will have to separately compile your program before running it by selecting Build Project from the Project menu
the reason to separate the two steps is to avoid problems when you make changes to the program and run it only to see the old version run because the new version did not compile
Most syntax errors will be caught before you compile and highlighted with an X on the line
move your mouse cursor over the X and it will display an error message
Output will appear at the bottom under the Console tab