This document summarizes key concepts from Chapter 4 of Head First Java including: 1. Methods can take arguments as parameters and return values or void. The Dog class bark method takes an int parameter and returns void. 2. Passing arguments uses pass by value where the method gets a copy of the value rather than a reference to the variable. 3. Reference variables pass object references, allowing methods to modify object properties. The Dog class uses getters and setters to encapsulate the size property rather than direct access.

1. Head First Java Chapter 4
Tom Henricksen

2. Sending to a method
● Arguments
● Parameters
Dog d = new Dog();
d.bark(3);
void bark (int numOfBarks) {

3. Method returns
● Void - void go() {...
● Value - int calculate score() { …
● Compiler

4. Let’s code
Dog
DogTestDrive

5. Pass by value
Int x = 7;
Void go(int z) {
Copy x into z

6. Reference Variables
● Pass one or more parameters
● Match parameters
● Promote type
● Pass literal or variables

7. Encapsulation
● Direct Access
● Use methods instead
dog.size = 50;
dog.setSize(50);

8. GoodDog
private int size;
public getSize() { return size;}
public setSize(int s) { size = s; }
int x = 3 + dog.getSize();

9. Object Arrays
Dog[] pets = new Dog[7];
pets[0].setSize(30);

10. Instance and local variables
● Instance variables
○ private int a;
○ private String name = “Dog”;
● Local variables
○ int s = 0;

11. Comparisons
● Primitives
○ byte a = 0; byte b = 0;
○ a == b;
● Object
○ dogA.equals(dogB); dogA == dogB;

12. Sharpen your pencil
Which method calls work?

13. Be the compiler
● Exercise B