4. Classes and Methods
9 likesâą2,207 views
The document discusses classes and methods in Java. It defines that a class is a user-defined data type that serves as a template to define properties. A class contains fields to store data and methods to perform actions. Methods are declared inside the class and can access and modify the class fields. The document also discusses creating objects from classes using the new keyword, using constructors to initialize objects, using this keyword to refer to class fields from methods, method overloading and static methods.
![Classes in Java
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
class Rectangle
{
int length, width; // combined declaration
void getData (int x, int y)
{
length = x;
width = y;
}
int rectArea ()
{
int area = length*width;
return (area);
}
}
class RectArea
{
public static void main (String arg[])
{
Rectangle rect1 = new Rectangle();
Rectangle rect2 = new Rectangle();
rect1.length = 10;
rect1.width = 10;
rect2.getData(10, 20);
System.out.println("Area 1: "+rect1.rectArea());
System.out.println("Area 2: "+ rect2.rectArea());
}
}](https://image.slidesharecdn.com/4-150303051431-conversion-gate01/85/4-Classes-and-Methods-8-320.jpg)
![Constructor
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
class Rectangle
{
int length, width; // combined declaration
Rectangle (int x, int y)
{
length = x;
width = y;
}
int rectArea ()
{
int area = length*width;
return (area);
}
}
class RectArea
{
public static void main (String arg[])
{
Rectangle rect = new (10, 20);
System.out.println("Area 1: "+ rect.rectArea());
}
}](https://image.slidesharecdn.com/4-150303051431-conversion-gate01/85/4-Classes-and-Methods-10-320.jpg)
![Static Members
Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
class StaticDemo
{
static float mul(float x, float y)
{
return x*y;
}
static float divide(float x, float y)
{
return x/y;
}
}
class StaticMain
{
public static void main(String arg [])
{
float a = StaticDemo.mul(4.0, 5.0);
float b = StaticDemo.divide(a, 2.0);
System.out.println("Value of b: "+b);
}
}](https://image.slidesharecdn.com/4-150303051431-conversion-gate01/85/4-Classes-and-Methods-15-320.jpg)
4. Classes and Methods
- 1. Classes and MethodsClasses and Methods By Nilesh Dalvi Lecturer, Patkar-Varde College.Lecturer, Patkar-Varde College. http://www.slideshare.net/nileshdalvi01 Java and Data StructuresJava and Data Structures
- 2. Classes in Java âą A class is a user-defined data type with a template that serves to define its properties. âą A class is declared by use of the class keyword. âą General form of class is: Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W). class classname { type instance-variable1; type instance-variable2; // type instance-variableN; type methodName(parameter-list) { //body of method } }
- 3. Classes in Java Field Declaration: Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W). class Rectangle { int length; int width; }
- 4. Classes in Java Method Declaration: âą Methods are declared inside the body of the class but immediately after the declaration of instance variable. âą The general form of method declaration id, âą Method declaration have four basic parts: â Name of the method (methodName) â Type of the value method return (type) â List of parameters (parameter - List) â Body of the method Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W). type methodName (parameter-list) { method-body; }
- 5. Classes in Java Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W). class Rectangle { int length, width; // combined declaration void getData (int x, int y) { length = x; width = y; } int rectArea () { int area = length*width; return (area); } }
- 6. Creating objects âą Object is a block of memory that contains space to store all the instance variable. âą Creating an objects is also called as instantiating an objects. âą Objects are created using new keyword. âą new operator creates an objects of the specified class and returns a reference to that object. âą Example: Rectangle rect; // Declare the objects rect = new Rectangle(); // instantiating the objects âą Both statement combined into one as follows, Rectangle rect = new Rectangle(); âą Each objects has its own copy of instance variable. Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
- 7. Accessing class members âą Using (.) operator we can access the class members i.e. properties of class. objectname.variablename = values; objectname.methodname(parameterlist); âą Example: rect.length = 10; rect.width = 20; rect.getData(10, 20); Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
- 8. Classes in Java Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W). class Rectangle { int length, width; // combined declaration void getData (int x, int y) { length = x; width = y; } int rectArea () { int area = length*width; return (area); } } class RectArea { public static void main (String arg[]) { Rectangle rect1 = new Rectangle(); Rectangle rect2 = new Rectangle(); rect1.length = 10; rect1.width = 10; rect2.getData(10, 20); System.out.println("Area 1: "+rect1.rectArea()); System.out.println("Area 2: "+ rect2.rectArea()); } }
- 9. Constructors âą Constructors is a special type of method in java which enables an object to initialize itself when it is created. âą Constructors name is same as class name. âą They do not specify return type, not even void. because it return the instance of class itself. Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
- 10. Constructor Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W). class Rectangle { int length, width; // combined declaration Rectangle (int x, int y) { length = x; width = y; } int rectArea () { int area = length*width; return (area); } } class RectArea { public static void main (String arg[]) { Rectangle rect = new (10, 20); System.out.println("Area 1: "+ rect.rectArea()); } }
- 11. this keyword âą this keyword can be used inside any method to refer to the current class instance variable. Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W). Rectangle (int length, int width) { this.length = length; this.width = width; }
- 12. Method Overloading âą it is possible to create method that have the same name, but different parameter lists and different definitions. Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
- 13. Nesting Method âą A method can be called only by its method name by another method of same class. âą This is known as nesting of method. Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
- 14. Static Members âą Like, static variable we can define static methods. âą In Java library, Math class defines many static methods to perform math operation that can be used in any program. float x = Math.sqrt(25.0); âą Static methods called using class name. âą Static methods have several restriction: â They can only call other static methods. â They can only access static data. â They can not refer to this or super in any program. Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W).
- 15. Static Members Nilesh Dalvi, Lecturer@Patkar-Varde College, Goregaon(W). class StaticDemo { static float mul(float x, float y) { return x*y; } static float divide(float x, float y) { return x/y; } } class StaticMain { public static void main(String arg []) { float a = StaticDemo.mul(4.0, 5.0); float b = StaticDemo.divide(a, 2.0); System.out.println("Value of b: "+b); } }
- 16. Q & A