The document discusses user defined methods in Java and provides examples of simple programs that utilize methods. Some key points covered include: - Advantages of using methods to organize and reuse code. - Examples of methods that perform basic operations like addition, average calculation, data type conversions, etc. - Passing arrays to methods and returning arrays from methods. - Differences between functions and methods in Java. - Overloading methods by changing the number and type of arguments. - Implementing methods to calculate operations like LCM, HCF, prime number checks, etc.

1. User Defined Methods in Java
With Animation

2. Index
1.
2.
Advantages
Simple Programs using Methods
a)
b)
c)
d)
e)
f)
g)
h)
i)
j)
k)
l)
m)
n)
o)
p)
q)
r)
Add two numbers
Average of three numbers
Circle area
Fahrenheit to Celsius
Check number is even or not
Check number is prime or not
Reverse of a number
Check number is palindrome or not
Count number of digits in a number
Sum of digits
LCM of 2, 3 and 4 numbers
HFC of 2 numbers
1 to 100 prime numbers
200 to 500 prime and palindrome
Decimal to binary, octal, hex
Binary to decimal, octal, hex
Octal to binary,decimal, hex
Hexadecimal to binary, octal, decimal
3.
Pass Array to Methods
a)
b)
c)
d)
e)
4.
Print all elements of an array
Sum of an array
Average of an array
Maximum element of an array
Minimum element of an array
Returning Array From Methods
a)
b)
Reverse array
Reverse every element of an array

3. Function v/s Method

4. Function v/s Method
Q.)What is the difference between a
function and a method.?

5. Function v/s Method
Q.)What is the difference between a
function and a method.?
Ans.) A method is a function that is
written in a class.

6. Function v/s Method
Q.)What is the difference between a
function and a method.?
Ans.) A method is a function that is
written in a class.
We do not have functions in java; instead we have methods. This means whenever a
function is written in java. It should be written inside the class
only. But if we take C++, we can write the functions inside as well as outside the class.
So in C++, they are called member functions and not methods.

7. Function with no arguments and no
return(no input no output)
void display()
{
System.out.println("this is inside method body");
}

8. Function with no arguments and no
return(no input no output)
void display()
{
System.out.println("this is inside method body");
}
When you want to return no value,
then set return type to void

9. Function with no arguments and no
return(no input no output)
Name of the
function is
“display”
void display()
{
System.out.println("this is inside method body");
}
When you want to return no value,
then set return type to void

10. Function with no arguments and no
return(no input no output)
Name of the
function is
“display”
No arguments
here
void display()
{
System.out.println("this is inside method body");
}
When you want to return no value,
then set return type to void

11. Complete Program
public class function1
{
static void display()
{
System.out.println("this is inside method body");
}
public static void main(String args[])
{
System.out.println("before function call");
display();
System.out.println("after function call");
}
}

12. Method
Definition
Complete Program
public class function1
{
static void display()
{
System.out.println("this is inside method body");
}
public static void main(String args[])
{
System.out.println("before function call");
display();
System.out.println("after function call");
}
}

13. Method
Definition
Complete Program
public class function1
{
static void display()
{
System.out.println("this is inside method body");
}
public static void main(String args[])
{
System.out.println("before function call");
display();
System.out.println("after function call");
}
}
Method
Calling

14. Add two integer numbers
int add(int a, int b)
{
int c=a+b;
return c;
}

15. Add two integer numbers
int add(int a, int b)
{
int c=a+b;
return c;
}
Two Integer
Arguments

16. Add two integer numbers
int add(int a, int b)
{
int c=a+b;
return c;
}
Returning integer value to calling method
Two Integer
Arguments

17. Complete Program
public class function1
{
static int add(int a, int b)
{
int c=a+b;
return c;
}
public static void main(String args[])
{
System.out.println(add(45,67));
}
}

18. Display method
is called
method,
because it is
called by main
method
Complete Program
public class function1
{
static int add(int a, int b)
{
int c=a+b;
return c;
}
public static void main(String args[])
{
System.out.println(add(45,67));
}
}

19. Display method
is called
method,
because it is
called by main
method
Complete Program
public class function1
{
static int add(int a, int b)
{
int c=a+b;
return c;
}
public static void main(String args[])
{
System.out.println(add(45,67));
}
}
main method
is calling
method,
because it is
calling display
method.

20. Average of three integer numbers
double
{
double d;
d=((double)a+b+c)/3;
return d;
}
)

21. Average of three integer numbers
double
{
double d;
d=((double)a+b+c)/3;
return d;
}
)
This method takes
multiple arguments and
returns single value

22. Average of three integer numbers
double
{
double d;
d=((double)a+b+c)/3;
return d;
}
)
This method takes
multiple arguments and
returns single value

23. Calculate circle Area
double
{
double area=Math.PI*radius*radius;
return area;
}

24. Calculate circle Area
double
{
double area=Math.PI*radius*radius;
return area;
}

25. Convert Fahrenheit to Celsius
double convertFahToCel(double fah)
{
double cel=(fah-32)*5/9;
return cel;
}

26. Convert Fahrenheit to Celsius
double convertFahToCel(double fah)
{
double cel=(fah-32)*5/9;
return cel;
}
This method takes one
argument and returns
single value

27. Check number is even or not
boolean checkEven(int n)
{
if(n%2==0)
{
return true;
}
else
{
return false;
}
}

28. Check number is even or not
boolean checkEven(int n)
{
if(n%2==0)
{
return true;
}
else
{
return false;
}
}

29. Check number is prime or not
boolean isPrime(int n)
{
int i;
for( i=2;i<n;i++)
{
if(n%i==0)
{
break;
}
}d
if(n==i)
{
return true;
}
else
{
return false;
}
}

30. Reverse number
int reverseNumber(int n)
{
int x=0;
for( ; n!=0 ; )
{
int r=n%10;
x=x*10+r;
n=n/10;
}
return x;
}

31. Check number is palindrome or not
boolean isPalindrome(int n)
{
int rev =
if(n==rev)
{
return true;
}
else
{
return false;
}
FOCUS ON ONE WORK
}
We need to focus on palindrome
not on reverse number code,
this is a advantage of method.
;

32. Check number is palindrome or not
boolean isPalindrome(int n)
{
int rev =
if(n==rev)
{
return true;
}
else
{
return false;
}
FOCUS ON ONE WORK
}
We need to focus on palindrome
not on reverse number code,
this is a advantage of method.
;
Using previous slide’s
reverse number method

33. Count number of digits in a number
This is Exercise

34. Sum of digits
This is Exercise

35. LCM(Lowest Common Multiple) of 2
numbers
long getLCM(int n1, int n2)
{
long answer=1;
for(int i=2;n1!=1 && n2!=1;)
{
if(n1%i==0 && n2%i==0)
{
n1=n1/i;
n2=n2/i;
answer=answer*i;
}
else if(n1%i==0)
{
n1=n1/i;
answer=answer*i;
}
else if(n2%i==0)
{
n2=n2/i;
answer=answer*i;
}
else
{
i++;
}
}//end of for loop
answer=n1*n2*answer;
return answer;
}//end of this method

36. LCM of 3 Numbers
long getLCM(int n1,int n2,int n3)
{
long result1 = getLCM(n1,n2);
long finalResult=getLCM((int) result1,n3);
return finalResult;
}

37. LCM of 3 Numbers
long getLCM(int n1,int n2,int n3)
{
long result1 = getLCM(n1,n2);
long finalResult=getLCM((int) result1,n3);
return finalResult;
}
Method overloading on getLCM() method
differ by number of arguments

38. LCM of 3 Numbers
long getLCM(int n1,int n2,int n3)
{
long result1 = getLCM(n1,n2);
long finalResult=getLCM((int) result1,n3);
return finalResult;
}

39. LCM of 3 Numbers
long getLCM(int n1,int n2,int n3)
{
long result1 = getLCM(n1,n2);
long finalResult=getLCM((int) result1,n3);
return finalResult;
}
User Defined
getLCM() 2 argument
method

40. LCM of 3 Numbers
long getLCM(int n1,int n2,int n3)
{
long result1 = getLCM(n1,n2);
long finalResult=getLCM((int) result1,n3);
return finalResult;
}

41. LCM of 3 Numbers
long getLCM(int n1,int n2,int n3)
{
long result1 = getLCM(n1,n2);
long finalResult=getLCM((int) result1,n3);
return finalResult;
}
Narrowing
type
conversion

42. LCM of 3 Numbers
long getLCM(int n1,int n2,int n3)
{
long result1 = getLCM(n1,n2);
long finalResult=getLCM((int) result1,n3);
return finalResult;
}

43. LCM of 4 Numbers
long getLCM(int n1,int n2,int n3, int n4)
{
long result1 = getLCM(n1,n2,n3);
long finalResult=getLCM((int) result1,n4);
return finalResult;
}

44. LCM of 4 Numbers
long getLCM(int n1,int n2,int n3, int n4)
{
long result1 = getLCM(n1,n2,n3);
long finalResult=getLCM((int) result1,n4);
return finalResult;
}
Method overloading on getLCM() method
differ by number of arguments

45. LCM of 4 Numbers
long getLCM(int n1,int n2,int n3, int n4)
{
long result1 = getLCM(n1,n2,n3);
long finalResult=getLCM((int) result1,n4);
return finalResult;
}

46. LCM of 4 Numbers
long getLCM(int n1,int n2,int n3, int n4)
{
long result1 = getLCM(n1,n2,n3);
long finalResult=getLCM((int) result1,n4);
return finalResult;
}
User Defined
getLCM() 3
arguments method

47. LCM of 4 Numbers
long getLCM(int n1,int n2,int n3, int n4)
{
long result1 = getLCM(n1,n2,n3);
long finalResult=getLCM((int) result1,n4);
return finalResult;
}

48. LCM of 4 Numbers
long getLCM(int n1,int n2,int n3, int n4)
{
long result1 = getLCM(n1,n2,n3);
long finalResult=getLCM((int) result1,n4);
return finalResult;
}
Narrowing
type
conversion

49. LCM of 4 Numbers
long getLCM(int n1,int n2,int n3, int n4)
{
long result1 = getLCM(n1,n2,n3);
long finalResult=getLCM((int) result1,n4);
return finalResult;
}

50. HCF(Highest Common Factor) of 2
numbers
int getHCF(int n1,int n2)
{
int lcmOfThese=(int) getLCM(n1,n2);
long product=n1*n2;
int hcfOfThese=(int)(product/lcmOfThese);
return hcfOfThese;
}

51. HCF(Highest Common Factor) of 2
numbers
int getHCF(int n1,int n2)
{
int lcmOfThese=(int) getLCM(n1,n2);
long product=n1*n2;
int hcfOfThese=(int)(product/lcmOfThese);
return hcfOfThese;
}
Narrowing type
conversion /manual type
casting/ down casting

52. HCF(Highest Common Factor) of 2
numbers
int getHCF(int n1,int n2)
{
int lcmOfThese=(int) getLCM(n1,n2);
long product=n1*n2;
int hcfOfThese=(int)(product/lcmOfThese);
return hcfOfThese;
}

53. HCF(Highest Common Factor) of 2
numbers
int getHCF(int n1,int n2)
{
int lcmOfThese=(int) getLCM(n1,n2);
long product=n1*n2;
int hcfOfThese=(int)(product/lcmOfThese);
return hcfOfThese;
}
User Defined getLCM()
method

54. Print prime numbers between 1 and
100
void printPrime1To100()
{
for(int i=1;i<=100;i++)
{
if(
==true)
{
System.out.println(i);
}
}
User
}
defined
method

55. Print prime numbers between 200 and 500
which are Palindrome numbers too
This is exercise

56. Convert Decimal to XXX
String convertDecimalToXXX(long n,int base)
{
StringBuilder sb = new StringBuilder();
for(;n!=0;n=n/base)
{
byte x= (byte)(n%base);
if(x>=10)
{
char ch=' ';
switch(x)
{
case 10:ch='A';break;
case 11:ch='B';break;
case 12:ch='C';break;
case 13:ch='D';break;
case 14:ch='E';break;
case 15:ch='F';break;
}
sb.append(ch);
}
else
{
sb.append(x);
}
}
return
String.valueOf(sb.reverse());
}

57. Convert Decimal to Binary
String convertDecimalToBinary(long n)
{
int base=2;
String ans=convertDecimalToXXX(n,base);
return ans;
}

58. Convert Decimal to Octal
String convertDecimalToOctal(long n)
{
int octal_base=8;
String ans=convertDecimalToXXX(n,octal_base);
return ans;
}

59. Convert Decimal to Hexadecimal
String convertDecimalToHexadecimal(long n)
{
int hex_base=16;
String ans=convertDecimalToXXX(n,hex_base);
return ans;
}

60. Convert Binary to XXX
long convertXXXToDecimal(int base,String num)
{
StringBuilder sb = new StringBuilder(num);
long sum=0,t=0;
for(int i=sb.length()-1;sb.length()!=0;i--,t++)
{
Character x=sb.charAt(i);
int y=x-48;
sb=sb.deleteCharAt(i);
double z=y*(Math.pow(base, t));
sum=sum+(long)z;
}
return sum;
}

61. Convert Binary to Decimal
long convertBinaryToDecimal(String binary_number)
{
int binary_base=2;
long ans=convertXXXToDecimal(binary_base,binary_number);
return ans;
}

62. Convert Octal to Decimal
long convertOctalToDecimal(String binary_number)
{
int binary_base=8;
long ans=convertXXXToDecimal(binary_base,binary_number);
return ans;
}

63. Convert Hexadecimal to Decimal
long convertHexToDecimal(String binary_number)
{
int binary_base=2;
long ans=convertXXXToDecimal(binary_base,binary_number);
return ans;
}

64. Convert Hexadecimal to Octal
String convertHexToOctal(String hexNumber)
{
long decimal=convertHexToDecimal(hexNumber);
String ans=convertDecimalToOctal(decimal);
return ans;
}

65. Convert Hexadecimal to Binary
String convertHexToBinary(String hexNumber)
{
long decimal=convertHexToDecimal(hexNumber);
String ans=convertDecimalToBinary(decimal);
return ans;
}

66. Convert Octal to Hexadecimal
String convertOctalToHex(String octalNumber)
{
long decimal=convertOctalToDecimal(octalNumber);
String ans=convertDecimalToHex(decimal);
return ans;
}

67. Convert Octal to Binary
String convertOctalToBinary(String octalNumber)
{
long decimal=convertOctalToDecimal(octalNumber);
String ans=convertDecimalToBinary(decimal);
return ans;
}

69. Print All elements of an Array
void arrayTraversing(int arr[])
{
for(int x:arr)
{
System.out.println(x);
}
}

70. Print All elements of an Array
void arrayTraversing(int arr[])
{
for(int x:arr)
{
System.out.println(x);
}
}

71. Print All elements of an Array
Method
Header /
Method
Declaration
void arrayTraversing(int arr[])
{
for(int x:arr)
{
System.out.println(x);
}
}

72. Sum of an Array
int sumOfArray(int arr[])
{
int sum=0;
for(int x:arr)
{
sum=sum+x;
}
return sum;
}

73. Sum of an Array
int sumOfArray(int arr[])
{
int sum=0;
for(int x:arr)
{
sum=sum+x;
Taking an integer
array and returning
}
single value of int
data type
return sum;
}

74. Average of an Array
float averageOfArray(int arr[])
{
int sum=0;
float avg;
for(int x:arr)
{
sum=sum+x;
}
avg=(float)sum/arr.length;
return avg;
}

75. Maximum of an Array
byte maximumOfArray(byte arr[])
{
byte max=Byte.MIN_VALUE;
for(byte x:arr)
{
if(x>max)
{
max=x;
}
}
return max;
}

76. Maximum of an Array
byte maximumOfArray(byte arr[])
{
byte max=Byte.MIN_VALUE;
for(byte x:arr)
{
if(x>max)
{
max=x;
}
}
return max;
}

77. Minimum of an Array
byte minimumOfArray(byte arr[])
{
byte min=Byte.MAX_VALUE;
for(byte x:arr)
{
if(x<min)
{
min=x;
}
}
return min;
}

78. Minimum of an Array
byte minimumOfArray(byte arr[])
{
byte min=Byte.MAX_VALUE;
for(byte x:arr)
{
if(x<min)
{
min=x;
}
}
return min;
}
Wrapper class for
byte data type

79. Minimum of an Array
byte minimumOfArray(byte arr[])
{
byte min=Byte.MAX_VALUE;
for(byte x:arr)
{
if(x<min)
{
min=x;
}
}
return min;
Maximum
}
value of
byte is 127.
Wrapper class for
byte data type

81. Return prime numbers between 1 and
100
A method cannot
int[] getPrime1To100()
return multiple
{
values but it can
int arr[] = new int[100];
return an array.
for(int i=1,j=1;
i<=100;i++)
{
if(
==true)
{
arr[j]=i;
j++;
}
}
Taking no parameters but
return arr;
returning an array.
}

82. Complete Program
public class function1
{
static int[] getPrime1To100()
{
int arr[] = new int[100];
for(int i=1,j=1;
i<=100;i++)
{
if(isPrime(i)==true)
{
arr[j]=i;
j++;
}
}
return arr;
}
public static void main(String args[])
{
int art[]=getPrime1To100();
for(int x:art)
{
if(x!=0)
{
System.out.println(x);
}
}
}//end of main method
}//end of public class
Array contains
100 values,
some are prime
numbers other
are default
values (0).

83. Reverse array
byte[] reverseArray(byte arr[])
{
Returning byte array to
calling method
byte xyz[]=new byte[100];
int i=arr.length-1;
for(j=0; i>=0; i-- , j++)
{
This method takes an
xyz[i]=arr[j];
array(multiple byte
}
type values) and
returns an
return xyz;
array(multiple byte
}
type values).

84. Original Array
5
78
Reverse array
89
1655
byte[] reverseArray(byte arr[])
{
Returning byte array to
calling method
byte xyz[]=new byte[100];
int i=arr.length-1;
for(j=0; i>=0; i-- , j++)
{
This method takes an
xyz[i]=arr[j];
array(multiple byte
}
type values) and
returns an
return xyz;
array(multiple byte
}
type values).

85. Original Array
5
78
Reverse array
89
1655
1655
Converted Array
89
78
5
byte[] reverseArray(byte arr[])
{
Returning byte array to
calling method
byte xyz[]=new byte[100];
int i=arr.length-1;
for(j=0; i>=0; i-- , j++)
{
This method takes an
xyz[i]=arr[j];
array(multiple byte
}
type values) and
returns an
return xyz;
array(multiple byte
}
type values).

86. Original Array
5
78
Reverse array
89
1655
1655
Converted Array
89
78
5
byte[] reverseArray(byte arr[])
{
Returning byte array to
calling method
byte xyz[]=new byte[100];
int i=arr.length-1;
for(j=0; i>=0; i-- , j++)
{
This method takes an
xyz[i]=arr[j];
array(multiple byte
}
type values) and
returns an
return xyz;
array(multiple byte
}
type values).

87. Reverse digits of all array elements 1
Example
Original Array
5
78
89
1655
464
782
346
75623
98
5561
464
287
643
32657
Converted Array
5
87

88. Reverse digits of all array elements 2
void reverseEveryArrayElement(int a[])
{
for(int i=0;i<a.length;i++)
{
a[i]=reverseNumber(a[i]);
}
}

89. Reverse digits of all array elements 2
void reverseEveryArrayElement(int a[])
{
for(int i=0;i<a.length;i++)
{
a[i]=reverseNumber(a[i]);
}
}
Replacing
every element
of array with
its reverse
number

90. Reverse digits of all array elements 2
void reverseEveryArrayElement(int a[])
{
for(int i=0;i<a.length;i++)
{
a[i]=reverseNumber(a[i]);
}
}
Replacing
every element
of array with
its reverse
number
This method is
modifying
original array
elements.

91. Complete Program
public static void main(String args[])
{
int a[]={5,78,89,1655,464,782,346,75623};
reverseEveryArrayElement(a);
arrayTraversing(a);
}
static void reverseEveryArrayElement(int a[])
{
for(int i=0;i<a.length;i++)
{
a[i]=reverseNumber(a[i]);
}
}

92. Advantages of Using Methods



48

93. Advantages of Using Methods
1. To help make the program more
understandable


48

94. Advantages of Using Methods
1. To help make the program more
understandable
2. To modularize the tasks of the program
– building blocks of the program

48

95. Advantages of Using Methods
1. To help make the program more
understandable
2. To modularize the tasks of the program
– building blocks of the program
3. Write a module once
– those lines of source code are called multiple times
in the program
48

96. Advantages of Using Methods



49

97. Advantages of Using Methods
4. While working on one function, you can focus on
just that part of the program
–
–
–
construct it,
debug it,
perfect it.


49

98. Advantages of Using Methods
4. While working on one function, you can focus on
just that part of the program
–
–
–
construct it,
debug it,
perfect it.
5. Different people can work on different functions
simultaneously.

49

99. Advantages of Using Methods
4. While working on one function, you can focus on
just that part of the program
–
–
–
construct it,
debug it,
perfect it.
5. Different people can work on different functions
simultaneously.
6. If a function is needed in more than one place in a
program, or in different programs, you can write it
once and use it many times
49