lecture 10 1Lecture 10 Review of classeshc293. I tried replying to your email, but you were over yourquota and it bounced.Aaron Macy. I tried replying to your email, but the reply addresswas [email protected], which does not exist. How did you dothat? I could not find you in the Cornell electronic directory. Seeme before/after class.The only inalienable right responsibility pain-in-the-butt ofAmericans is to receive email. anonymousGod answers knee-mail. anonymouslecture 10 2Assignment A3 handed out todayDue next Friday.Class NoSuchElementException is defined in package java.util.Do not put a throws clause in your method headers unless theprogram won’t compile without it. You cannot put one in a methodthat is required by an implements-clause.To make an apptmnt for a one-on-one:With Gries: Call Cindy Pakkala at 255-8240With a TA: See them at recitation or contact them --see website fordetails.With a consultant. Go to Upson 304 or Purcell during office hours.If you can’t take it then, sign up on the sign-up sheet.lecture 10 3ReviewSee the Java bootcamp slides.Look at the beginning of Weiss.Read ProgramLive, chaps. 1, 3, 4.Listen to lectures on ProgramLive.lecture 10 4ClassesAssume you know the basics of a class definition. Think of aclass as a file-drawer, and the class definition gives the format ofall the manilla folders (objects) in the file-drawer. So, a classdefinition is a template.All non-static components (variables, methods) go in each folder.All static components go directly in the file-drawer, along withall the folders. There is only one copy of each of the staticcomponents.lecture 10 5Classpublic class C {private int x; private double y;public void m1(int) { …}public int m2() { … }}a0Cxy5truem1(int) m2()Object drawn like amanilla folderTab contains nameof object (address inmemory)public components can be referencedanywhere; private ones only in theclass itself.Generally, but not always, fields areprivate and methods are public.a0vv contains a pointer to, reference to,or the name of the object.lecture 10 6Summary of classes• Class defines content of file drawer and format of objects:• File drawer contains static components and created objects,drawn as manilla folders. The name of an object —itslocation in memory— is drawn on the tab of the folder.• new-expression, used to create objects. Know the 3 steps inevaluating it.• Constructor: called in new-expression to initialize fields.• Use of private and public.• Getter and setter methods.• static vs. non-static variables (instance variables or fields).• static vs. non-static methods (instance methods).• Method toString.• Two uses of keyword this.lecture 10 7use of thispublic class C{ int x; int y; // Constructor: … public C (int x, int y;) { this.x= x;this.y= y} // Constructor: … public C(int y) { this(0, y); y= y+1; }}when used in this fashion, thisrefers to the object in whichmethod C occurs. So, this.xrefers to component x of theobject.when used in this fashion, you have aconstructor call on a constructor inthis class. Must be first statement inconstructor.lecture 10 8SubclassesCirclea0ShapegetArea()compareTo(Object)getPerimeter()radius2.0Circle(double)getRadius()getArea()getPerimeter()toString()ObjecttoString()equals(Object)ShapegetArea()compareTo(Object)getPerimeter()Squareside4.0Square(double)getSide()getArea()getPerimeter()toString()a1ObjecttoString()equals(Object)Object: thesuperest class ofthem all. Extendsall classes thatdon’t explicitlyextend another.Has moremethods. Wedon’t alwaysdraw it.overriding methodinherited methodlecture 10 9Subclassespublic abstract class Shape implements Comparable { /** = … */ public int compareTo(Object ob) { … } // = the area of the shape public abstract double getArea(); // = the circumference of the shape public abstract double getPerim();}public class Square extends Shape { private double side; /** Constructor: …/ public Square(double s) { side= s; } public double getSide() { return side; } public double getArea() { return side * side; } public double getPerimeter() { return 4 * side; } public String toString() { return "Sq: " + side; }}lecture 10 10is-a relationpublic abstract class Shape implements Comparable { /** = … */ public int compareTo(Object ob) { … } …}public class Square extends Shape { private double side; /** Constructor: …/ public Square(double s) { side= s; } …}When designing a set of classes, use the is-a relation to help youdecide about subclasses.If a square is a shape, then make Square a Subclass of Shape.The subclass has more properties than the superclass.lecture 10 11Two uses of superpublic class S { /** = … */ private int s; // Constructor: … public C(int s) {this.s= s; } public int m(int p) { … }}public class T extends S { private double t; /** Constructor: …/ public SS(int s, double t) { super(s); this.t= t; } public int m(int p) { … int x= super.m(p); }} When used in this fashion,super refers to the superclasspartition of the object inwhich method m occurs. Here,super.m(p) calls this method.When used in this fashion,you have a constructor callon a constructor in thesuperclass. Must be firststatement in constructor.lecture 10 12Apparent type: type with which a variable is declared. Itdetermines what can be referenced. Syntactic property.public class CompDemo { public static void main(String[] pars) { Shape[] sh= new Shape[8]; sh[0]= new Circle(0); sh[4]= new Square(0); … }}Apparent type of s[0]: Shape.Only these are legal: sh[0].toString(), sh[0].equals(…),sh[0].getArea(), sh[0].getPerimeter(), sh[0].compareTo(…).a0ShapegetArea()compareTo(Object)getPerimeter()ObjecttoString()equals(Object)lecture 10 13Real type: type of object that is in thevariable. It determines is actually referenced.Semantic property.public class CompDemo { public static void main(String[] pars){ Shape[] sh= new Shape[8]; sh[0]= new Circle(0); sh[4]= new Square(0); … }}Circlea0ShapegetArea()compareTo(Object)getPerimeter()radius2.0Circle(double)getRadius()getArea()getPerimeter()toString()ObjecttoString()equals(Object)sh[0].getArea() calls thissh[0]a0lecture 10
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