I'm a Java newbie and I'm trying to deploy a fibonacci trail through recursive function and then calculate the run time. here is the code I have managed to write:
class nanoTime{
int fib(int n){
if(n==0) return 0;
if(n==1) return 1;
return this.fib(n-1)+this.fib(n-2);
}
public static void main(String[] args){
double beginTime,endTime,runTime;
int n=10;
beginTime = System.nanoTime();
n = this.fib(n);
endTime = System.nanoTime();
runTime = endTime-beginTime;
System.out.println("Run Time:" + runTime);
}
}
The problem is when I'm trying to turn it into Byte-code I get the following error:
nanoTime.java:11: non-static variable this cannot be referenced from a static context
I'm wondering what is the problem?!
Change
n = this.fib(n);
to
n = fib(n);
and make the method fib
static.
Alternatively, change
n = this.fib(n);
to
n = new nanoTime().fib(n);
您需要实例化nanoTime
以调用实例方法,或者使fib
方法也是静态的。
The problem is just what the message says. Your main
method is static
, which means it is not linked to an instance of the nanoTime
class, so this
doesn't mean anything. You need to make your fib
method static
as well, and then use nanoTime.fib(n)
.
There is no reason to use this
in your code.
Steps to take:
this
from your code static
keyword before int fib(int n){
# Name the class something else to avoid confusion between System.nanoTime and the name of your class.
class nanoTime1{
int fib(int n){
if(n==0) return 0;
if(n==1) return 1;
return this.fib(n-1)+this.fib(n-2);
}
public static void main(String[] args){
double beginTime,endTime,runTime;
int n=10;
beginTime = System.nanoTime();
# Instantiate an object of your class before calling any non-static member function
nanoTime1 s = new nanoTime1();
n = s.fib(n);
endTime = System.nanoTime();
runTime = endTime-beginTime;
System.out.println("Run Time:" + runTime);
}
}
Be careful ! In Java the main has to be in a class definition, but it's only the entry point of the program and absolutely not a method of the object/class.
Change this.fib(n)
to :
nano obj = new nano();
n = obj.fib(n);
this
is associated with the instance of the class. A static method does not run with a class instance but with the class itself. So either change the fib
method to static
or replace the line where you call fib
to the above two lines.
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