Class & Object - User Defined Method
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Class & Object - User Defined Method

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Chapter 6-2

Chapter 6-2

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  • Ada 2 kategori method <br /> 1.Method yg dpt pulangkan nilai-guna return <br /> 2.Void methodtak dpt pulangkan nilai <br />
  • Ada 2 kategori method <br /> 1.Method yg dpt pulangkan nilai-guna return <br /> 2.Void methodtak dpt pulangkan nilai <br />
  • Semasa panggilan method dilakukan, boleh ada lebih dari satu jenis data pada parameter. <br />
  • Sintak untuk memanggil method yang boleh pulangkan nilai (mesti ada parameter semasa panggilan dilakukan) <br />
  • Method methodABC() merupakan satu contoh method overloading dalam satu kelas <br />

Class & Object - User Defined Method Class & Object - User Defined Method Presentation Transcript

  • 1 User Defined Class
  • Syntax: Defining Class  General syntax for defining a class is: modifieropt class ClassIdentifier { classMembers: data declarations methods definitions }  Where modifier(s) are used to alter the behavior of the class classMembers consist of data declarations and/or methods definitions. 2
  • Class Definition  A class can contain data declarations and method declarations 3 int size, weight; char category; Data declarations Method declarations
  • UML Design Specification 4 UML Class Diagram Class Name What data does it need? What behaviors will it perform? Public methods Hidden information Instance variables -- memory locations used for storing the information needed. Methods -- blocks of code used to perform a specific task.
  • Class Definition: An Example  public class Rectangle  { // data declarations  private double length;  private double width;  //methods definitions  public Rectangle(double l, double w) // Constructor method  {  length = l;  width = w;  } // Rectangle constructor  public double calculateArea()  {  return length * width;  } // calculateArea  } // Rectangle class 5
  • Method Definition  Example 6  The Method Header modifieropt ResultType MethodName (Formal ParameterList ) public static void main (String argv[ ] ) public void deposit (double amount) public double calculateArea ( ) public void MethodName() // Method Header { // Start of method body } // End of method body
  • Method Header  A method declaration begins with a method header 7 int add (int num1, int num2) method name return type Formal parameter list The parameter list specifies the type and name of each parameter The name of a parameter in the method declaration is called a formal parameter
  • Method Body  The method header is followed by the method body 8 int add (int num1, int num2) { int sum = num1 + num2; return sum; } The return expression must be consistent with the return type sum is local data Local data are created each time the method is called, and are destroyed when it finishes executing
  • User-Defined Methods  Methods can return zero or one value Value-returning methods ○ Methods that have a return type Void methods ○ Methods that do not have a return type 9
  • calculateArea Method. public double calculateArea() { double area; area = length * width; return area; } 10
  • Return statement  Value-returning method uses a return statement to return its value; it passes a value outside the method.  Syntax:return statement return expr;  Where expr can be: Variable, constant value or expression 11
  • User-Defined Methods  Methods can have zero or >= 1 parameters No parameters ○ Nothing inside bracket in method header 1 or more parameters ○ List the paramater/s inside bracket 12
  • Method Parameters - as input/s to a method public class Rectangle { . . . public void setWidth(double w) { width = w; } public void setLength(double l) { length = l; } . . . } 13
  • Syntax: Formal Parameter List (dataType identifier, dataType identifier....) 14 Note: it can be one or more dataType Eg. setWidth( double w ) int add (int num1, int num2)
  • Creating Rectangle Instances  Create, or instantiate, two instances of the Rectangle class: 15 The objects (instances) store actual values. Rectangle rectangle1 = new Rectangle(30,10); Rectangle rectangle2 = new Rectangle(25, 20);
  • Using Rectangle Instances  We use a method call to ask each object to tell us its area: 16 rectangle1 area 300 rectangle2 area 500Printed output: System.out.println("rectangle1 area " + rectangle1.calculateArea()); System.out.println("rectangle2 area " + rectangle2.calculateArea()); References to objects Method calls
  • Syntax : Object Construction  new ClassName(parameters); Example:  new Rectangle(30, 20);  new Car("BMW 540ti", 2004); Purpose:  To construct a new object, initialize it with the construction parameters, and return a reference to the constructed object. 17
  • The RectangleUser Class Definition public class RectangleUser { public static void main(String argv[]) { Rectangle rectangle1 = new Rectangle(30,10); Rectangle rectangle2 = new Rectangle(25,20); System.out.println("rectangle1 area " + rectangle1.calculateArea()); System.out.println("rectangle2 area " + rectangle2.calculateArea()); } // main() } // RectangleUser 18 An application must have a main() method Object Use Object Creation Class Definition
  • Method Call  Syntax to call a method methodName(actual parameter list); Eg. segi4.setWidth(20.5); obj.add (25, count); 19
  • Formal vs Actual Parameters  When a method is called, the actual parameters in the invocation are copied into the formal parameters in the method header 20 int add (int num1, int num2) { int sum = num1 + num2; return sum; } total = obj.add(25, count);
  •  public class RectangleUser  {  public static void main(String argv[])  {  Rectangle rectangle1 = new Rectangle(30.0,10.0);   System.out.println("rectangle1 area " +  rectangle1.calculateArea()); rectangle1.setWidth(20.0);  System.out.println("rectangle1 area " +  rectangle1.calculateArea());  }  } 21 Formal vs Actual Parameters
  • Method Overloading  In Java, within a class, several methods can have the same name. We called method overloading  Two methods are said to have different formal parameter lists: If both methods have a different number of formal parameters If the number of formal parameters is the same in both methods, the data type of the formal parameters in the order we list must differ in at least one position 22
  • Method Overloading  Example: public void methodABC() public void methodABC(int x) public void methodABC(int x, double y) public void methodABC(double x, int y) public void methodABC(char x, double y) public void methodABC(String x,int y) 23
  • Java code for overloading  public class Exam  {  public static void main (String [] args)  {  int test1=75, test2=68, total_test1, total_test2;  Exam midsem=new Exam();  total_test1 = midsem.result(test1);  System.out.println("Total test 1 : "+ total_test1);  total_test2 = midsem.result(test1,test2);  System.out.println("Total test 2 : "+ total_test2);  }  int result (int i)  {  return i++;  }   int result (int i, int j)  {  return ++i + j;  }  } 24
  •  Output Total test 1 : 75 Total test 2 : 144 25
  • Constructors Revisited  Properties of constructors: Name of constructor same as the name of class A constructor,even though it is a method, it has no type Constructors are automatically executed when a class object is instantiated A class can have more than one constructors – “constructor overloading” ○ which constructor executes depends on the type of value passed to the constructor when the object is instantiated 26
  • Java code (constructor overloading) public class Student { String name; int age; Student(String n, int a) { name = n; age = a; System.out.println ("Name1 :" + name); System.out.println ("Age1 :" + age); } Student(String n) { name = n; age = 18; System.out.println ("Name2 :" + name); System.out.println ("Age2 :" + age); } public static void main (String args[]) { Student myStudent1=new Student("Adam",22); Student myStudent2=new Student("Adlin"); } } 27
  • 28 Output: Name1 :Adam Age1 :22 Name2 :Adlin Age2 :18
  • Object Methods & Class Methods  Object/Instance methods belong to objects and can only be applied after the objects are created.  They called by the following : objectName.methodName();  Class can have its own methods known as class methods or static methods 29
  • Static Methods  Java supports static methods as well as static variables.  Static Method:-  Belongs to class (NOT to objects created from the class)  Can be called without creating an object/instance of the class  To define a static method, put the modifier static in the method declaration:  Static methods are called by : ClassName.methodName(); 30
  • Java Code (static method) public class Fish { public static void main (String args[]) { System.out.println ("Flower Horn"); Fish.colour(); } static void colour () { System.out.println ("Beautiful Colour"); } } 31
  • 32 Output: Flower Horn Beautiful Colour