User Defined Methods in Java


User Defined Methods in Java
 

i) Introduction to Java Methods

ii) Types of Methods

iii) User defined Methods
-----------------------------------
i) Introduction to Java Methods

1) What is Method?
 

> A Java method is a set of statements that are grouped together to perform an operation.

> Methods are also known as Functions

> In Structured programming (ex: C Language) we use Functions (Built in and User defined)

> In Object Oriented Programming we use Methods (Built in and User defined)

2) When we choose Methods?
 

Whenever we want to perform any operation multiple times then choose methods.

3) Advantages of Methods
 

Code Reusability and Reduce the project code size.
---------------------------------
ii) Types of Methods
 

Basically we have 2 types of Methods

    1) Built in Methods

    2) User defined Methods
-----------------------------
1) Built in Methods
 

Java has a library of classes and methods organized in packages.

Ex:

import java.io.Console;

import java.io.*;

> In order to use built in methods we need to import packages or classes.

> java.lang package is automatically imported in every Java program.

> Using import keyword we can import packages/classes.
-----------------------------------------
Categories of Built in Methods.
 

    1) String Methods

    2) Array Methods

    3) Number Methods

    4) Character Methods
    Etc....
---------------------------------
iii) User defined Methods
 

Two types of User defined Methods
 

1) Method without returning any value
        a) Calling Method by invoking Object
        b) Calling Method without invoking Object

2) Method with returning a value.
-------------------------------
        a) Calling Method by invoking Object
        b) Calling Method without invoking Object
---------------------------------------------------
1) Writing Methods (With returning a value)

a) Syntax for creating a method (calling the method by invoking object)

 

Write Method
//Before main Method
accessModifier returnType methodName(Parameters){
Statements
---------
---------
------
}
----------------------
//After main method
Call Method
//Create Object
ClassName objectName = new ClassName();

//Call Method y invoking object
dataType variableName = object.method(values..);
Or
System.out.println(object.method());
-----------------------------------
Example:
 

package xyza;

public class JavaMethods {

//User defined Method
public int multiply(int a, int b, int c){
int result = a * b * c;
return result;
}

public static void main (String [] args){

//Create Object
JavaMethods abc = new JavaMethods();

//Call Method
int x = abc.multiply(10, 25, 35);
System.out.println(x);
   
System.out.println(abc.multiply(10, 25, 35));
}
}
------------------------------------------------
1) Writing Methods (With returning a value)

b) Syntax for creating a method (calling the method without object)

 

accessModifier nonAccessModifier returnType methodName(Parameters){
Statements
------
------
------
}
Call Method

dataType variableName = methodName(values);

Or
System.out.println(methodname(values);
------------------------------------------
Example:
 

package xyza;

public class JavaMethods {

//Create Method
public static int multiply(int a, int b, int c){
int result = a * b * c;
return result;
}

public static void main (String [] args){
//Call Method
int x = multiply(10, 25, 35);
System.out.println(x);
   
System.out.println(multiply(10, 25, 35));
}
}
-----------------------------------------
2) Write method without returning any value

a) Syntax for creating a Method (call the method by invoking Object)


accessModifier returnTypeNothing methodName(parameters){
Statements
----------
----------
---------
}

//Create Object
ClassName objectName = new ClassName();

//Call Method
object.method(values);
-------------------------------------
Example:
 

public class JavaMethods {

//Create Method
public void studentRank(int marks){
if (marks >= 600){
System.out.println("Rank A");
}
else if (marks >= 500){
System.out.println("Rank B");
}
else
System.out.println("Rank C");
}

public static void main (String [] args){

//Call method by invoking object
JavaMethods obj = new JavaMethods();
obj.studentRank(600);
}
}
------------------------------
2) Write method without returning any value
b) Syntax for creating a Method (call the method without Object)
 

accessModifier nonAccessModifier returnTypeNothing methoName(Parameters){
Statements
---------
---------
---------
}
Call method

methodName(values);
----------------------------------
public class JavaMethods {

//Create Method without returning any value (without object)
public static void studentRank(int marks){
if (marks >= 600){
System.out.println("Rank A");
}
else if (marks >= 500){
System.out.println("Rank B");
}
else{
System.out.println("Rank C");
}
}

public static void main (String [] args){

//Call method without object
studentRank(450);
}
}
------------------------------------------
Usage of methods
 

a) Internal methods (defining/creating and calling methods within the same class)
b) External methods (Calling methods from other classes)
------------------------------------
3a) Call External method (from another class) -by invoking Object
Class 1:
 

public class Sample1 {
//Create Method
public static int multiply(int a, int b, int c){
int result = a * b * c;
return result;
}
}

Class 2: 



public class Sample2 {
//Create method
public int add(int a, int b, int c){
int result = a + b + c;
return result;
}
   
public static void main (String [] args){

//Create Object
Sample2 obj1 = new Sample2();

//Calling Internal method
int x = obj1.add(10, 25, 35);
System.out.println(x);

//Create Object   
Sample1    obj2 = new Sample1();

//Calling External Method
int y = obj2.multiply(10, 25, 35);
System.out.println(y);
}
}
-----------------------------
3b) Call External method (from another class) -without Object

Class 1:
 

public class Sample1 {

//Create Method
public static void studentRank(int marks){
if (marks >= 600){
System.out.println("Rank A");
}
else if (marks >= 500){
System.out.println("Rank B");
}
else{
System.out.println("Rank C");
}
}

public static void main (String [] args){
//Call method without object
studentRank(450);
}
}

Class 2:
 

public class Sample2 {

public static void main (String [] args){
Sample1.studentRank(450);
}
}
-----------------------------------
Other Topics:
 

1) Method OverLoading

2) Method OverRiding
-------------------------------------

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