Java methods or Subroutines or Functions

Java Methods, Method Overloading, Recursion

1. User defined Subroutines/ Methods
/ Functions
in Java
Dr. Kuppusamy.P
Associate Professor / SCOPE

2. UserdefinedmethodsinJava
•Methodisacollectionofstatementsgroupedtogethertoperforman
operation.
•Usercanalsodefinemethodsinsideaclasscalleduser-defined
methodsorsubroutinesorfunctions.
•Anuserdefinedmethodwillrunonlywhenitiscalled.
•Usercanpassdata,knownasparameters/arguments,intoa
method.
•Whyaremethodsneeded?
•CodeReusability:Definethecodeonce,useitmanytimes.
Dr. Kuppusamy P

3. CreatingMethod
•Methoddefinitionconsistsofamethodheaderandamethodbody.
Syntax
modifierreturnTypenameOfMethod(ParameterList)
{
//bodywithSetofStatements
}
•modifier−definestheaccesstypeofthemethodanditisoptional.
•returnType−Methodmayreturnavalueorvoidanditismandatory.
•nameOfMethod−methodnameisanyuserdefinedname.
•ParameterList−Thelistofparameters,datatype,order,andnumberof
parameters.Theseareoptional,methodmaycontainzeroparameters.
•methodbody−Setofstatementsperformaspecifictask.
Dr. Kuppusamy P

4. Method-Example
publicstaticvoidfindFact()//MethodDefinition
{
Scannersin=newScanner(System.in);
intn=sin.nextInt();
intf=1;
for(inti=1;i<=n;i++)
f=f*i;
System.out.println(f);
}
//Methodcalling
publicstaticvoidmain(Stringargs[])
{
findFact();
}
Dr. Kuppusamy P

5. CreatingMethod
Methodcanbecreatedinthefollowingfourways
1.Methodwithoutreturn-typewithoutparameters
2.Methodwithoutreturn-typewithparameters
3.Methodwithreturn-typewithoutparameters
4.Methodwithreturn-typewithparameters
5.Staticmethods
6.Non-staticmethods
Dr. Kuppusamy P

6. CreatingMethod-Example
1.Methodwithoutreturn-typewithoutparameters
publicclassFactEx
{
publicvoidFact() //MethodDefinition
{
Scannersin=newScanner(System.in);
intn=sin.nextInt();
intf=1;
for(inti=1;i<=n;i++)
f=f*i;
System.out.println(f);
}
//Methodcalling
publicstaticvoidmain(Stringargs[])
{
Fact();
}
}
Dr. Kuppusamy P

7. CreatingMethod-Example
2.Methodwithoutreturn-typewithparameters
publicclassFactEx1
{
publicvoidFact(intn) //MethodDefinition
{
intf=1;
for(inti=1;i<=n;i++)
f=f*i;
System.out.println(f);
}
//Methodcalling
publicstaticvoidmain(Stringargs[])
{
Scannersin=newScanner(System.in);
intn=sin.nextInt();
Fact(n);
}
}
Dr. Kuppusamy P

8. CreatingMethod-Example
3.Methodwithreturn-typewithoutparameters
publicclassFactEx2
{
publicintFact() //MethodDefinition
{
Scannersin=newScanner(System.in);
intn=sin.nextInt();
intf=1;
for(inti=1;i<=n;i++)
f=f*i;
returnf;
}
//Methodcalling
publicstaticvoidmain(Stringargs[])
{
intfactorial=Fact();
System.out.println(factorial);
}
}
Dr. Kuppusamy P

9. CreatingMethod-Example
4.Methodwithreturn-typewithparameters
publicclassFactEx3
{
publicintFact(intn) //MethodDefinition
{
intf=1;
for(inti=1;i<=n;i++)
f=f*i;
returnf;
}
//Methodcalling
publicstaticvoidmain(Stringargs[])
{
Scannersin=newScanner(System.in);
intinp=sin.nextInt();
intfactorial=Fact(inp);
System.out.println(factorial);
}
}
Dr. Kuppusamy P

10. CreatingMethod-Example
5.Staticmethods
publicclassStaticEx{
publicstaticintFact(intn) //methoddefinition
{
intf=1;
for(inti=1;i<=n;i++)
f=f*i;
returnf;
}
publicstaticvoidmain(String[]args)
{
Scannersin=newScanner(System.in);
intnum=sin.nextInt();
intfactorial=Fact(num); //methodcalling
System.out.println(factorial);
}
}
Dr. Kuppusamy P

11. CreatingMethod-Example
6.Non-staticmethods
publicclassNonStaticEx{
publicintFact(intn) //methoddefinition
{
intf=1;
for(inti=1;i<=n;i++)
f=f*i;
returnf;
}
publicstaticvoidmain(String[]args)
{
Scannersin=newScanner(System.in);
intnum=sin.nextInt();
NonStaticExm=newNonStaticEx(); //objectorinstancecreationfortheclassNonStaticEx
intfactorial=m.Fact(num); //methodcalling
System.out.println(factorial);
}
}
Dr. Kuppusamy P

12. Passing arrays as Parameters
Dr. Kuppusamy P

13. PassingarraysasParameters
•Passarraystoamethodlikenormalvariables.
•Whenpassanarrayasanargument,actuallytheaddressofthe
arrayinthememoryispassed(reference).
CreatingMethodwithArrays
i.Withoutreturnanarray
modifierreturnTypeMethodname(data-typearray-name[])
{
//methodbody
}
ii.Withreturnanarray
modifierdata-type[]Methodname(data-typearray-name[])
{
//methodbody
}
Dr. Kuppusamy P

14. Example
importjava.util.*;
publicclassArrayPass
{
publicintmin(int[]array)
{
intmin=array[0];
for(inti=0;i<array.length;i++)
{
if(array[i]<min)
{
min=array[i];
}
}
returnmin;
}
Dr. Kuppusamy P

15. Example
publicstaticint[]descending(int[]array)
{
for(inti=0;i<array.length;i++)
{
for(intj=i+1;j<array.length;j++)
{
if(array[i]>array[j])
{
temp=array[i];
array[i]=array[j];
array[j]=temp;
}
}
}
returnarray;
}
Dr. Kuppusamy P

16. Example
publicstaticvoidmain(Stringargs[])
{
Scannersc=newScanner(System.in);
intsize=sc.nextInt();
int[]myArray=newint[size];
for(inti=0;i<size;i++)
{
myArray[i]=sc.nextInt();
}
ArrayPassm=newArrayPass();
intmax=m.min(myArray);
System.out.println(max);
intdsc[]=m.descending(myArray);
for(inti:dsc)
System.out.println(i);
}
}
Dr. Kuppusamy P

17. Method Overloading in java
Dr. Kuppusamy P

18. MethodOverloadinginjava
•MethodOverloadingisaclasscontainsmorethanonemethodwiththesamemethod
name.Butvaryingtheargumentlistslikecount,datatypeandargumentssequence.
•Example:
•Additionoftwonumberforintegeraswellasfloat.
•Advantages
•Methodoverloadingincreasesthereadabilityoftheprogram.
Differentapproachesofmethodoverloading
1.Numberofparameters.
•add(inta,intb)
•add(inta,intb,intc)
2.Datatypeofparameters.
•add(inta,intb)
•add(inta,floatb)
3.SequenceofDatatypeofparameters.
•add(int,float)
•add(float,int)
Dr. Kuppusamy P

19. MethodOverloadinginjava
importjava.util.Scanner;
publicclassOverload
{
publicstaticintadd(inta,intb)
{
returna+b;
}
publicstaticfloatadd(floata,floatb)
{
returna+b;
}
publicstaticvoidadd(floata,intb)
{
System.out.println(a+b);
}
publicstaticvoidmain(Stringargs[])
{
Scannersc=newScanner(System.in);
intnum1=sc.nextInt();
intnum2=sc.nextInt();
intisum=add(num1,num2);
floatfsum=add(34.34f,34.34f);
add(10.0f,20);
System.out.println(fsum);
}
}
Dr. Kuppusamy P

20. Recursion in java
Dr. Kuppusamy P

21. Recursioninjava
•Recursionisaprocessinwhichamethodcallsitselfcontinuously.
•Amethodinjavathatcallsitselfiscalledrecursivemethod.
•Itmakesthereusabilityofcode.So,reducestheprogramsize.
•Syntax
returntypemethodname()
{
statements;
methodname();
}
Dr. Kuppusamy P

22. Factorialusingrecursioninjava
•Example
importjava.util.*;
publicclassRecFact
{
publicstaticintfact(intn)
{
if(n<=1)
{
System.out.println(n);
return1;
}
else
{
System.out.print(n+"*");
returnn*fact(n-1);
}
}
publicstaticvoidmain(String[]args)
{
intn;
System.out.println("Enterthenotofind
factorial");
Scannersin=newScanner(System.in);
n=sin.nextInt();
intres=fact(n);
System.out.println("Factorial"+res);
}
}
Dr. Kuppusamy P

23. FibonacciusingRecursioninjava
•Example
importjava.util.*;
publicclassFibRec{
publicstaticintfib(intn)
{
if(n==0)
{
return0;
}
if(n==1||n==2)
{
return1;
}
else
returnfib(n-2)+fib(n-1);
}
publicstaticvoidmain(String[]arg)
{
intn;
Scannersin=newScanner(System.in);
System.out.println("Enterthefib
series");
n=sin.nextInt();
for(inti=0;i<=n;i++)
{
System.out.print(fib(i)+"");
}
}
}
Dr. Kuppusamy P

24. References
Dr. Kuppusamy P
Herbert Schildt, “Java: The Complete Reference”, McGraw-Hill Education, Tenth edition,
2017.