Review

1
Review

• View classes as modules
• Encapsulate operations
• Functions are static methods
• View classes as struct types
• Encapsulate data
• View classes as abstract data types
• Encapsulate both data and operations

2
Life Cycle of Objects

• Creating objects
• Using objects
• Cleaning up unused objects
• An object becomes garbage when no variable refers
  to it

Point p new Point(0,0) Stack s new Stack()
p.x 100 rx s.pop()
3
Class Declaration in Java

public abstract final class ClassName
extends ClassName implements Interfaces
VariableDeclaration ConstructorDeclaratio
n MethodDeclaration
ClassDeclaration InterfaceDeclaration
4
Declaring Variables
AccessSpecifier static final type
VariableName

• Access Specifier
• public accessible from anywhere
• private within the class
• (default) within the class and the package
• protected within the package and subclasses
• static class variable
• final constant
• Examples

5
Method Declarations
MethodDeclaration MethodHead
MethodBody MethodHead AccessSpecifier
static final ReturnType MethodName(T1
p1, ..., Tn pn) MethodBody
LocalVariableDeclarationStatement
ClassOrInterfaceDeclaration Identifier
Statement
signature
6
Method Overloading

• A class can contain multiple methods that have
  the same name but different signatures

class C int m(int i) return i1
double m(double f) return f2
7
Constructor

• Constructor
• Has the same name as the class
• A class can have any number of constructors
• Has no return value
• Uses "this" to call other constructors in the
  class

8
Scope of Method Arguments
class Circle int x, y, radius
public Circle(int x, int y, int radius)
this.x x this.y y
this.radius radius
9
The Meaning of "static"

• A static variable or method belongs to the class
• A static variable is shared by all objects of the
  class

class C public static void main(String
args) int a 10 int b
20 System.out.println(max(a,b))
int max(int x, int y) return
(xgty) ? x y
What is wrong?
10
Static Variables (exercise)
class AnIntegerNamedX static int x
public int x() return x
public void setX(int newX) x newX

AnIntegerNamedX myX new AnIntegerNamedX() AnInt
egerNamedX anotherX new AnIntegerNamedX() myX.s
etX(1) anotherX.x 2 System.out.println("myX.x
" myX.x()) System.out.println("anotherX.x
" anotherX.x())