Introduction
Continue4Each method has its own name. When that name is
encountered in a program, the execution of the program branches to
the body of that method. When the method is finished, execution
returns to the area of the program code from which it was called,
and the program continues on to the next line of code.
Methods6There are two basic types of methods: Built-in: Build-in
methods are part of the compiler package, such as
System.out.println( ) and System.exit(0).
User-defined: User-defined methods are created by you, the
programmer. These methods take-on names that you assign to them and
perform tasks that you create.
Built-in Methods7Java Provides some Method for common
mathematical calculations e.g.Calculate the square root of
900.0:Math.sqrt( 900.0 )Method sqrt belongs to class MathDot (.)
allows access to method sqrtThe argument 900.0 is located inside
parenthesesClassMethod which belongs to class MathThis always
performs actions. Parameters or data passed to method to perform an
actionAdvantageBreak large programs into a series of smaller
modulesHelps manage complexityMakes it easier to build large
programsMakes it easier to debug programsMost of the time, you need
to know what a function does, but not how it actually does it.You
use other peoples code without knowing how it does its job.
8
Some Built-in Math Functions Method Declarations (cont.)9General
format of method declaration:
modifiers return-value-type method-name( parameter1, ,
parameterN ){ declarations and statements}Method can also return
values:Methods Declarations10Parameters or argumentsValues that is
to be passed into the Method, or the value on which the function
will operate. It may be a int, float, char or String.Returned
ValueThe value which is returned by the Method after applying the
code on it. It may be a int, float, char or String.Local
variablesDeclared and used in method declaration (its scope is the
method only)
ProgramImport Java.util.Scanner;Class Square{public static void
main(String arg[]){Scanner input = new Scanner(System.in);int
val;val=input.nextInt();int res;res=
findSqr(val);System.out.println(Square = + res);}public static int
findSqr( int x){return x*x;}} ProgramImport Java.util.ScannerClass
Square{public static void main(String arg[]){Scanner input = new
Scanner(System.in);int val;val=input.nextInt();int res;res=
findSqr(val);System.out.println(Square = + res);}public static int
findSqr( int x){return x*x;}} Function NameReturn
typeParameters13Classes and Objects in JavaBasics of Classes in
Java14IntroductionJava is a true OO language and therefore the
underlying structure of all Java programs is classes.Anything we
wish to represent in Java must be encapsulated in a class that
defines the state and behaviour of the basic program components
known as objects.Classes create objects and objects use methods to
communicate between them. They provide a convenient method for
packaging a group of logically related data items and functions
that work on them.15ClassesA class is a collection of fields (data)
and methods (procedure or function) that operate on that data.
Circlecentreradius
circumference()area()
16ClassesA class is a collection of fields (data) and methods
(procedure or function) that operate on that data.The basic syntax
for a class definition:
Bare bone class no fields, no methods
public class Circle { // my circle class}class ClassName
[extends SuperClassName]{ [fields declaration] [methods
declaration]}17Adding Fields: Class Circle with fieldsAdd
fields
The fields (data) are also called the instance varaibles.
public class Circle { public double x, y; // centre coordinate
public double r; // radius of the circle
}18Adding MethodsA class with only data fields has no life.
Objects created by such a class cannot respond to any
messages.Methods are declared inside the body of the class but
immediately after the declaration of data fields.The general form
of a method declaration is:type MethodName
(parameter-list){Method-body;}19Adding Methods to Class
Circlepublic class Circle {
public double x, y; // centre of the circle public double r; //
radius of circle
//Methods to return circumference and area public double
circumference() { return 2*3.14*r; } public double area() { return
3.14 * r * r; }}Method Body20Object DeclarationObjects are the
existence of class in memory, members of class is accessed through
the object of a class.
Can define variables (objects) of that type:
Circle aCircle;Circle bCircle;21Class of Circle cont.aCircle,
bCircle simply refers to a Circle object, not an object itself.
aCirclePoints to nothing (Null Reference)bCirclePoints to nothing
(Null Reference)nullnull22Creating objects of a classObjects are
created dynamically using the new keyword.aCircle and bCircle refer
to Circle objects
bCircle = new Circle() ;aCircle = new Circle() ;23Creating
objects of a classaCircle = new Circle();bCircle = new Circle()
;
bCircle = aCircle;24Creating objects of a classaCircle = new
Circle();bCircle = new Circle() ;
bCircle = aCircle;PaCircleQbCircleBefore
AssignmentPaCircleQbCircleBefore Assignment25Automatic garbage
collectionThe object does not have a reference and cannot be used
in future.
The object becomes a candidate for automatic garbage
collection.
Java automatically collects garbage periodically and releases
the memory used to be used in the future.
Q26Accessing Object/Circle DataSimilar to C syntax for accessing
data defined in a structure.
Circle aCircle = new Circle();
aCircle.x = 2.0 // initialize center and radiusaCircle.y =
2.0aCircle.r =
1.0ObjectName.VariableNameObjectName.MethodName(parameter-list)
27Executing Methods in Object/CircleUsing Object Methods:Circle
aCircle = new Circle();
double area; aCircle.r = 1.0;area = aCircle.area();sent message
to aCircle28Using Circle Class// Circle.java: Contains both Circle
class and its user class//Add Circle class code hereclass MyMain{
public static void main(String args[]) { Circle aCircle; //
creating reference aCircle = new Circle(); // creating object
aCircle.x = 10; // assigning value to data field aCircle.y = 20;
aCircle.r = 5; double area = aCircle.area(); // invoking method
double circumf = aCircle.circumference();
System.out.println("Radius="+aCircle.r+" Area="+area);
System.out.println("Radius="+aCircle.r+" Circumference ="+circumf);
}}[raj@mundroo]%: java MyMain Radius=5.0 Area=78.5Radius=5.0
Circumference =31.400000000000002MethodDescriptionExample
abs( x )absolute value of x (this method also has float, int and
long versions)abs( 23.7 ) is 23.7
abs( 0.0 ) is 0.0
abs( -23.7 ) is 23.7
ceil( x )rounds x to the smallest integer not lessthan xceil(
9.2 ) is 10.0
ceil( -9.8 ) is -9.0
cos( x )trigonometric cosine of x (x is in radians)cos( 0.0 ) is
1.0
exp( x )exponential method exexp( 1.0 ) is 2.71828
exp( 2.0 ) is 7.38906
floor( x )rounds x to the largest integer not greater than
xfloor( 9.2 ) is 9.0
floor( -9.8 ) is -10.0
log( x )natural logarithm of x (base e)log( Math.E ) is 1.0
log( Math.E * Math.E ) is 2.0
max( x, y )larger value of x and y (this method also has float,
int and long versions)max( 2.3, 12.7 ) is 12.7
max( -2.3, -12.7 ) is -2.3
min( x, y )smaller value of x and y (this method also has float,
int and long versions)min( 2.3, 12.7 ) is 2.3
min( -2.3, -12.7 ) is -12.7
pow( x, y )x raised to the power y (xy)pow( 2.0, 7.0 ) is
128.0
pow( 9.0, 0.5 ) is 3.0
sin( x )trigonometric sine of x (x is in radians)sin( 0.0 ) is
0.0
sqrt( x )square root of xsqrt( 900.0 ) is 30.0
sqrt( 9.0 ) is 3.0
tan( x ) trigonometric tangent of x (x is in radians)tan( 0.0 )
is 0.0
Math-class methods.
