4. What Does Object
Oriented Mean?
• If Ikea were made of code, it would totally
be written in an Object Oriented language.
• Object-Oriented means that we break our
code down into components (objects) with
properties (fields), that can be used to
make other objects, or interact with each
other.
• (See? It’s a little bit like Ikea furniture!)
5. OK, Give Me an
Example!
• Imagine a bike. If we wanted to “code” a bike, it
would be a lot easier if we split it down into its
component parts.
• wheels (x2)
• breaks
• seat
• frame
• peddles...
6. Another?
• How about a ToDo list?
• It’s make up of tasks.
• Each task should have things associated with it, such as:
• It’s name
• The date it’s due
• The date we actually complete it
• An estimate of how long it will take
• The date we started it
7. Try It!
• Think of a complex object
• Break it down into it’s component parts
• What information does each component
need to know about itself?
9. Eclipse is a powerful, free and open source Java IDE
(Integrated Development Environment). It has some
very useful features for learning to program.
10. Let’s start by making a new project.
File => New => Java Project
11. Let’s call it “Hello World”.
It’s a programming tradition.
12. Now we make a new “class”. Java classes
are where we represent our “objects”.
13. Let’s call this “HelloWorld”. Notice how
there are no spaces? That’s important.
16. Finally! Write Some
Code
• For our first program, we’re going to write
something that prints out “Hello World” in
the terminal.
• (Sorry, programmer tradition)
17. Click on “Run” (the green “play
button), and see what happens.
18. What Does It All Mean?
• public class HelloWorld {
• Declares our class/object with name “HelloWorld”. Everything inside the “{“ is part of the
class. Public is to do with it’s visibility (don’t worry about that for now).
•
public static void main(String[] args) {
• This is our “main” method, what’s called when we click “run”. The String[] args means
we can pass arguments to it, if we want to. Everything inside the “{“ is part of the main
method.
•
System.out.println("Hello World");
• This means - print out “Hello World” to the terminal. The “;” is important, it denotes the
end of the line of code. We’re going to be using a lot of these.
•
} }
• The first closing bracket denotes the end of the “main” method, the second the end of the
HelloWorld class.
20. Building Blocks
• Primitives are the most basic kinds of “type”
in Java (a building block!)
• You can also think of them as like atoms in
chemistry.
• A “type” is where we say what kind of thing
a variable is.
• Objects are made up of other objects and
primitives.
21. For Example...
• Whole numbers, like 42, or 926 are of type
int (or short, or long).
• Decimal numbers, like 2.34376 or 1.203 are
float, or double.
• True or False are boolean.
• A character like ‘a’ or ‘c’ is a char. Notice
the single quotes? Those are important.
22. Declaring Variables
• We can declare a variable of a primitive type in Java as
follows:
• int i = 42;
• double d = 735.27;
• boolean b = true;
• char c = ‘h’;
• So:
• type variable_name = value;
23. See how we can use the “+” sign to
include it in our output?
25. Strings
• A String is not a primitive, it’s an Object,
but we can declare it like a primitive.
• It’s a little more complex to declare
Objects (but we’ll look at that later)
• String s = “hello world”;
• String s = “hello world” + “nhow are you?”
27. Comparing Things
• We compare things in • Equals: ==
Java using conditional
logic. • Greater Than: >
• We can put this in an “if • Less Than: <
statement”
• Greater Than or
• if (a == b ) { ... } Equal To: >=
• else if (a < b) { ... } • Less Than or Equal
To: <=
• else { ... }
30. Repeating Things
• Loops are helpful for sections of code
that we want to repeat.
• There are three kinds of loop.
• while
• do while
• for
31. For Loops
• For when we know how many times
we want to repeat something.
• 10 times
• for(int i = 0; i < 10; i++)
• For each character in a string
• for(int i = 0; i < stringname.length(); i++)
33. For each character in a string. s.charAt(i) gets
the character in the string at position i.
34. While and Do-While
Loops
• When we want to repeat something until a
condition changes.
• In a while loop we check that condition at the
start of the loop
• while(a == b) { ... }
• In a do-while loop we check that condition at
the end of the loop.
• do { ... } while (a == b)
38. Tidy Code
• Tidy code is much easier to read (and debug!)
• Debug - fix when it’s not working.
• As a rule, indent in one inside each set of {}.
• In longer sections of code, we can use // to denote a
comment.
• A comment is code that is ignored by the compiler.
• The Java compiler ignores whitespace, so use line breaks
wherever you think it will make your code clearer.
40. Finally
• This slide deck covers the very basics of
Java - the building blocks.
• It’s important to understand these, because
everything else builds upon them.
• Next, we’re going to look at Processing.