1. How Objects Behave
Chapter 4

2. Methods
Up until this point, our methods haven’t done much – displaying methods
We know how to instantiate objects and how to call them
The power is in Passing the method’s data = giving those methods data and they can react based on the information.

3. Page 73 Dog Class and Dog Test Drive
Bark Method –decision-making we’re familiar with – conditional stmts based on size
Dog TestDrive – new Object – one.size = 70
Two.size = 8; three.size = 35
Call the method Bark – result is different based on size
Each object has a bark method
Instance variables for each method are different

4. You can pass values (send things) to a Method
Page 74 – Very Important Concept
Up until this point a method name has had blank parentheses: Example d.bark()
Specify the type of data you pass it in ()
A method uses parameters - what is req’d
A caller passes arguments
d.bark(3)
Look at example – bottom of page 74

5. You can get things back from a method
Bark method Example on p. 74 doesn’t return anything
Void means the method does not return a value; it just does something.
Methods can return values
Must put the data type of the value you are sending back

6. Example
int theSecret = life.giveSecret() int giveSecret () { return 42; } Data type that you are sending back must declare a data type; what you say you’ll give back you better give back

7. Returning Numbers Sometimes methods need to do calculations;
Sometimes need to figure something out or come up with an answer
The method then needs to “send it back”

8. Page 76 – Sending things back
You can send more than one thing to a method
Look at example – page 76
Methods can have multiple parameters
Separate with commas
Separate the arguments with commas
You can pass variables into a method, as long as the variable type matches the parameter type. Example page 76 at bottom
t. takeTwo(12, 34)
12 and 34 are passed into x and y
Value of foo and value of bar become x and y

9. Page 77 Java is pass-by-value That means pass-by-copy
Big idea – you can pass one, two …. Values separated by commas
Most of the time we will be passing variables – the value of the variable to the method
Also, you are passing a copy of the method; original stays the same.

10. Page 82 Encapsulating the GoodDog class
Want to make sure that the user is forced to use an accurate value for the class
Instance variable called size of type integer
GetSize and SetSize
When we create new objects and we want to assign our object a size, we have to call the SetSize method.

11. Encapsulation Getter and Setter Methods
Allows you to protect methods so that numbers that are out of range, etc. don’t get entered in.
You accomplish this by making the instance variable private, rather than public
Variable is only available within the class
Getter and setter methods are public

12. New object One.setSize(70)
one based on GoodDog class
One.setSize(70)
70 passed into the setSize method
We can put checks and balances into the program to be sure that variables are assigned correctly

13. GetSize Method
GetSize – must be changed to the data type that we are returning.
Way to make sure other programmers use the classes appropriately.
Responsible for returning a data type that we’re returning
One.GetSize
A failsafe to be sure that other programmers use your methods appropriately.

14. Private methods - encapsulating
Private means that this variable size is private to this class
Things inside this class – methods – are the only ones that have access to the variable within the class
Getter and setter methods will be used to interact
You can only access using the getter & setter

15. Instance Variables & Local Variables
Important to know what they’re set to and how they react Page 84-85
Variable declarations need a name and a type
You can initialize and assign a value.
What is the value of the variable before you assign a value? Explanation page 84
Number primitives value = 0; boolean’s value =false; object reference variables value null.

16. Page 85 Difference between instance variables and local variables
Instance variables – declared inside a class, but NOT within a method
Local variables – declared within a method
Local variables must be initialized before you use them.
Example – page 85