1. Review 4 View classes as modules Encapsulate operations Functions are static methods 4 View classes as struct types Encapsulate data 4 View classes as abstract data types Encapsulate both data and operations

2. Point p = new Point(0,0); Stack s = new Stack(); Life Cycle of Objects 4 Creating objects 4 Using objects 4 Cleaning up unused objects –An object becomes garbage when no variable refers to it p.x = 100; rx = s.pop();

3. Class Declaration in Java [public] [abstract] [final] class ClassName [extends ClassName] [implements Interfaces] { [VariableDeclaration | ConstructorDeclaration | MethodDeclaration | ClassDeclaration | InterfaceDeclaration]* }

4. Programming in Java4 Declaring Variables –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 [AccessSpecifier] [static] [final] type VariableName

5. Programming in Java5 Method Declarations MethodDeclaration ::= MethodHead MethodBody MethodHead ::= [AccessSpecifier ] [static] [final] ReturnType MethodName(T1 p1,..., Tn pn) MethodBody ::= { [LocalVariableDeclarationStatement | ClassOrInterfaceDeclaration | [Identifier :] Statement ]* } signature

6. Method Overloading 4 A class can contain multiple methods that have the same name but different signatures class C { int m(int i){ return i+1; } double m(double f){ return f+2; }

7. Programming in Java7 Constructor 4 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. Programming in Java8 Scope of Method Arguments class Circle { class Circle { int x, y, radius; int x, y, radius; public Circle(int x, int y, int radius) { public Circle(int x, int y, int radius) { this.x = x; this.x = x; this.y = y; this.y = y; this.radius = radius; this.radius = radius; }}

9. The Meaning of "static" 4 A static variable or method belongs to the class 4 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 (x>y) ? x : y; } What is wrong?

10. Programming in Java10 Static Variables (exercise) class AnIntegerNamedX { static int x; static int x; public int x() { public int x() { return x; return x; } public void setX(int newX) { public void setX(int newX) { x = newX; x = newX; }} AnIntegerNamedX myX = new AnIntegerNamedX(); AnIntegerNamedX anotherX = new AnIntegerNamedX(); myX.setX(1); anotherX.x = 2; System.out.println("myX.x = " + myX.x()); System.out.println("anotherX.x = " + anotherX.x());