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CREATED BY: PRIYANKA PAREEK
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INTRODUCTION
Program: is a set of instructions given tocomputer. These instructions initiate some
action and sometimes called as executable
instructions. In Java programs instructions are specified
through Methods or functions.
Methods or Function is a sequence of somedeclaration statements and executable
statements.
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Amethod is a separatepiece of codethat
can be called by a main program or anyother method to perform some specific
function.
The following are characteristics of methods:
It can return one or no values
It may accept as many parameters it needs or no
parameter at all. Parameters are also called
function arguments. After the method has finished execution, it goes
back to the method that called it.
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WHY METHODS?
To Cope With Complexity
Hiding Details
Reuse
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METHOD/ FUNCTION DEFINITION
A method or a function is a sequence of
statements that carry out specific task(s)
Amethod or function must be defined before itis used anywhere in the program:
[access- specifier ] [modifier] return-type
method name (parameter list)
{
body of the method
}
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Where
access specifier : can be either public or
protected or private. Default is friendly modifier: can be one of: final, native,
synchronized, transient, volatile.
return-type: specifies the type of value that thereturn statement of the method returns. If no
value being returned, it should be void.
Method-name: valid java identifier.
Parameter list: it is a comma-separated list of
variables of a method referred to as its arguments
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METHOD PROTOTYPE AND SIGNATURE:
AMethod Prototypeis the first line of the
method definition that tells the program about the
type of the value returned by the method and the
number and type of arguments.
Method Signature: it basically refers to the
number and types of arguments. It is a part of the
method prototype.
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USE OF KEYWORD VOID
Methods not returning in any value are declared void
methods i.e., having void s their return type.
syntax: void methods-name(parameter list);
example:void setLabelText( )
{
jLabel.setText(### Thank U###);
}
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9
Methods Methods in Java define the behavior of the class.
Methods are similar to procedures or subroutines in otherlanguages.
The real benefits of object orientation come from hiding theimplementation of a class behind its operations.
Methods access the internal implementation details of a class
that are hidden from other objects. Hiding data behind methods is so fundamental to object
orientation it has a name - encapsulation.
Methods have zero or more parameters.
A method can have a return value.
A method's statements appear in a block of curly braces { and }that follow the method's signature.
public void speak () {
System.out.println("Hey Barney ...");
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INVOKING A METHOD
Provide an object reference and the method name,separated by a dot (.):
fred.speak();
Parameters are passed to methods as a comma-separated list.
A method can return a single value as a result, suchas an int:
public int add (int a, int b) {
return a+b;
}
A method can return no result:public void setFirstName (String firstName) {
this.firstName = firstName;
}
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Example: to print cube of a given number using
a method:
private voidComputeActionPerformed(java.awt.event.ActionEvent
evt) {
double n =Double.parseDouble(jTextField1.getText());
double res = CalcCube(n);
jLabel3.setText("" +res); }
double CalcCube(double b){
double cu = b * b * b;
return cu; }1/19/2011 Created By: PRIYANKA PAREEK 12
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ACTUAL AND FORMAL PARAMETERS
Actual parameters: are
the parameters
appearing in the method
call statement.
Formal parameters:
are the ones that appear
in method definition.
Example:
Formal Parameters:
int mult (int x, int y) {
return x* y;
}
Actual parameters:
int length = 10;
int width =5;
Int area = mult(length,
width);1/19/2011Created By: PRIYANKA PAREEK
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Arguments to Methods
Arguments to methods can be:
of primitive data types i.e. char, byte, short, int,
long, float, double, boolean.
of reference data types i.e. objects or arrays
A method is invoked in two manners: Call by
Value and Call by Reference. These two
ways are also called as Pass By Value and Passby Reference.
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Call by Value (or Pass By Value )
When a pass-by-value occurs, the method makes a copy ofthe value of the variable passed to the method. The
method cannot accidentally modify the original argument
even if it modifies the parameters during calculations.
In the given example, we called the method test and
passed the value ofias parameter. The value of i is copied
to the variable of the methodj. Sincej is the variable
changed in the test method, it will not affect the variable
value ifi in main since it is a different copy of the
variable.
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Call by Value (or Pass By Value )
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Call by Reference(or Pass by Reference)
When a pass-by-reference occurs, the reference toan object is passed to the calling method. This
means that, the method makes a copy of the
reference of the variable passed to the method.However, unlike in pass-by-value, the method
can modify the actual object that the reference is
pointing to, since, although different references
are used in the methods, the location of the datathey are pointing to is the same.
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Call by Reference(or Pass by Reference)
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Figure : Pass-by-referenceexample
A common misconception about pass-by-reference in Java is when
creating a swap method using Java references. Take note that
Java manipulates objects 'by reference, but it passes object
references to methods 'by value.'"As a result, you cannot write a
standard swap method to swap objects.
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Returning from a method
A method returns value through return statement. A method terminates when either a return
statement is encountered or the last statement in
the method is executed. Areturn statement is used to terminate a method
whether or not it returns a value.
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RETURNING VALUES
They may of three types of methods in Java:Computational Methods: these are the methods
that calculate or compute some value and returned
the computed value. Example: Math.sqrt () and
Math.cos( ) are computational methods.
Computational methods always return a computed
result.
ManipulativeMethods: these are the methodsthat manipulate information and return a success or
failure code.
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Procedural methods: these are the methods that
perform an action and have no explicit returnvalue. Example: System.out.println() method.
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SCOPE REVISITED
The scopedetermines where in the programthe variable is accessible. The scope also
determines the lifetime of a variable or how
long the variable can exist in memory. The
scope is determined by where the variable
declaration is placed in the program.
Def: The program part(s) in which a particular
piece of code or a data value(e.g.. Variable)
can be accessed is known as the piece-of-
codes or variables Scope.
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CONSTRUCTORS C
onstructors: a member method with thesame name as its class is called Constructor
and it is used to initialize the objects of that
class type with a legal initial value.
Example:
class A( ){
int a;
float b;public A( ){
a = 0;
b = 0.0; } }
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