0. Introduction to Programming with Java, for Beginners
Intro to Math Class
Concept of static
API Tour
Intro Random Class

1. Java Library
Java provides a huge library or collection of useful programs
A gold mine of well-tested code that can save you countless hours of development time
This huge library information is provided in API -Application Programming Interface

2. The Math Class Description provided in Java API
Collection of common math functions (sin, cos, sqrt, etc.).
And two constants: PI and E
> Math.PI
> Math.E
> Math.sqrt(25)
5.0
> Math.pow(2,10)
1024
> Math.cos(0)
1.0
> Math.cos(2 * Math.PI)

3. How the Math Class Works
public class Math{
public static final double PI = ;
public static double sin(double d){ .. }
public static double sqrt(double d) { .. }
private Math(){} .. }
> Math.PI
> Math.sqrt(25)
5.0

4. What's different about Math Class
It’s different from a typical Java class
It is a “stateless” class
We only need one Math class (not multiple instances)
No need to instantiate it (hence, no public constructor)
All of its variables and methods are static
static means “applies to the class as a whole” vs. “applies to an individual instance”

5. Static Data or Methods
A class can have data and methods of its own (not part of the objects)
For example, Dog class can keep a count of the number of objects it has created
class Dog{
static int dogCount; //not an instance variable …
Dog(String dogName, int dogAge){
name = dogName;
age = dogAge;
dogCount++; //short form for dogCount = dogCount +1 }

6. Static (contd..) In Dr Java
>Dog d1 = new Dog(“Fluffy”, 5);
>Dog d2 = new Dog(“Fido”, 6);
>Dog.dogCount 2
Dog.dogCount is asking Dog class for the count of the dogs created
Since dogCount belongs to class and not the object
Hence use the classname and not Object name to access variable dogCount
More on static topic next time

7. Using Reading Library (API)
We will use API documentation for Java Version 5
Find the documentation for the Math class
If you scroll down the lower left panel and click on the link labeled Math, the large "main" panel on the right will display the documentation for the Math class

8. General Class Interface
A class' public interface
Notice the four headings in the main panel.
Field Summary
Has information about public variables
Constructor and Method summaries
Describe the public constructors and methods
Method Detail
Provides detail on method inputs (parameter(s))and output (return type) and some extra details
The collection of all of a class' public fields, constructors, and methods constitute its "interface", that is, the public face that it shows the world.
Note that private variables and methods are not a part of its interface.

9. Math Class Description
Notice the phrase java.lang at the top of the main panel above the word Math
This means that the Math class is part of the core Java language and hence can be used directly
Math Class Interface
Field Summary: Has two constants PI and E
Constructor Summary: has no public constructor
Methods Summary: many methods all which are static
Method Details: e.g. sqrt() takes a double and returns a double

10. Packages and import Statements
If a class is not part of java language i.e. java.lang, you'll see package name
What is a package?
Basically it's a directory that has a collection of related classes
E.g. Random Class description contains: java.util.Random
Indicating that the Random code is stored in a file called java/util/Random.class somewhere on your machine.
The java/util directory/folder is known as the "util", or utility package.
Since Random is not part of Java Language we need to tell Java where to find it by saying
import java.util.Random;
Another way is to use the asterisk "wildcard character": import java.util.*;

11. Random Class A class to create Random numbers
Constructor Summary shows the objects of this type can be created
E.g. Random r = new Random();
Method Summary shows that it can generate random values of types:
integers, doubles etc.
E.g. r.nextInt(6) – Generate a integer numbers between 0 (inclusive) and 6 (exclusive)
How do I generate a number between 1 and 6 ?