Java Reference
In-Depth Information
Caution
Youcannotusethisformofthereturnstatementinaconstructorbecause
constructors do not have return types.
Invoking Methods Recursively
Amethodnormallyexecutesstatementsthatmayincludecallstoothermethods,suchas
printDetails()
invoking
System.out.println()
. However, it is occasion-
ally convenient to have a method call itself. This scenario is known as
recursion
.
Forexample,supposeyouneedtowriteamethodthatreturnsa
factorial
(theproduct
ofallthepositiveintegersuptoandincludingaspecificinteger).Forexample,3!(the!
is the mathematical symbol for factorial) equals 3×2×1 or 6.
Yourfirstapproachtowritingthismethodmightconsistofthecodepresentedinthe
following example:
int factorial(int n)
{
int product = 1;
for (int i = 2; i <= n; i++)
product *= i;
return product;
}
Although this code accomplishes its task (via iteration),
factorial()
could also
be written according to the following example's recursive style.
int factorial(int n)
{
if (n == 1)
return 1; // base problem
else
return n*factorial(n-1);
}
Therecursiveapproachtakesadvantageofbeingabletoexpressaprobleminsimpler
termsofitself.Accordingtothisexample,thesimplestproblem,whichisalsoknownas
the
base problem
, is 1! (1).
Whenanargumentgreaterthan1ispassedto
factorial()
,thismethodbreaksthe
problemintoasimplerproblembycallingitselfwiththenextsmallerargumentvalue.
Eventually, the base problem will be reached.
For example, calling
factorial(4)
results in the following stack of expressions:
