methodname(Rectangle

1、OOP Mega RecapClasses, objects, aliasing, methods, arrays, stringsObjects and classesObjects are “large” variablesGroup together multiple smaller primitive variablesObject variables themselves are aliases to the objectThe object itself is separate; its creation is a separate stepThe type of an objec

2、t is programmer definedcalled a classclass.type = variable;class = objectAccess member variablesmember variables using the . (dot) symbol.OOP Principle #0: Encapsulation (data hiding)Aliasing and Object ConstructionAn object variable doesnt contain the data itself!Object variables are hence called r

3、eference reference variablesvariablesThey referrefer to the objects present in memoryMultiple object variables can refer to the samesame object in memory!Object variable declaration: ;Assignment (=) creates aliases (not copies)Object creation = newnew ()();“new ()” is an expressiontype = class-namev

4、alue = alias to the newly created objectMethods (non-static)Can work on member variables of the objectA method is called “on an object”.method_name()The code inside a method can implicitly use member variablesThe member variables of the given object are usedStatic vs Non-static methodsstatic void me

5、thod_name(int parameter) /statements No object context to work with (simple)static void method_name(Rectangle r, int parameter) Explicit object context to work with (indirect, cumbersome)void method_name(int parameter)/ access member variablesImplicit object contextThe ConstructorA special methodNam

6、ed after the class name.Takes input parameters; no return typeno return type.Used to initialize an object at creation time.class RectangleRectangle(int w, int h)/statements;Multiple methods and recursionMethods of a class can call each other directlyEach implicitly use the same object contextsame ob

7、ject context.Recursive calls also implicitly use the same object same object contextcontext.The this keywordA special read-onlyread-only variable visible inside methodsAlias to the object context in useOrganizing and Reusing classesDependency relationship between classesMotivated by the dependency b

8、etween methodsHow should we re-use classes?Wrong Answer: Use copy and paste Trivial Answer: use objects of some classes inside other classesOOP Answer: Inheritance of classesParent-Child like relationship between classeseg. Parallelogram and Rectangle classesOOP feature #1:InheritanceDefine a new (“

9、child”) class based on a “parent” classThe new class has an implicit copy of the old class in itAdd member variables and re-define (override) some methodsUse the “super” alias to access parent class methodsMainly for calling parents constructor and overridden methodsImplicit copy of parents member v

10、ariablesThe child class gets a copy of the parents member variablesUse them freely as if they were defined in the child class itselfImplicit presence of parents methodsFreely use parents methodsThey work on the copy of parents member variables in the child classInheritance:Java syntaxclass extends /

11、 declarations for child class/ access parent version of overridden methodsuper.()/ access parents constructor/ must be first statement in child constructorsuper();Note: a child class can have a sub-child class and so on The “Object” classIts the parent class of allall classesImagine Java automatically adding an “extends Object”methods in ObjectString toString()returns a string rep