Issue translating script from python to java

Question

I have a script, first written in python, then in java. With the given arguments, 100,50,9,3, the python script yields 1630. For some reason, the java version yields -22. Why is this? Is there a logic error in the java code?

Python:

def calcPopulation(E,P,R,Y):
 if E > 1000 or P > 100 or R > 50 or Y > 10:
 print("One or more values that you entered is too high")
 return None
 elif Y == 1:
 return E*2
 males = E
 females = E
 #^For first year
 for i in range(Y-1): #males
 males -= int((P*males)/100)
 for i in range(Y-1):
 females += int(-(P*females)/100)
 for i in range(int(females)):
## femalebaby = (R/2)
## malebaby = (R/2)
 females+= (R/2)
 males+= (R/2)
 return int(males+females)
def main():
 print(calcPopulation(100,50,9,3))
 #Result is 1630
if __name__=="__main__":
 main()

Java:

import java.util.*;
public class rabbit{
 public static int calcPopulation(int E,int P,int R,int Y){
 if (E>1000||P>100||R>50||Y>10){
 System.out.print("One or more of the values you entered is too high");
 return 0;
 }
 else if (Y==1){
 return E*2;
 }
 int males=0;
 int females=0;
 males += (int) E;
 females += (int) E;
 for(int i=0;i<(Y-1);i++){
 males -= (int) (P*males)/100;
 }
 for(int i=0;i<(Y-1);i++){
 females -= (P*females)/100;
 for(int x=0;x<females;x++){
 females += (R/2);
 males += (R/2);
 }
 }
 return (int) (males+females);
 }
 public static void main(String[] args){
 System.out.println(calcPopulation(100,50,9,3));
 //Result produces -22
 }
}

My best guess is that the for loops in the java code are operating differently than the python ones? I'm not sure, since i'm just a noob in java. Bottom line is I need the java script to produce the same result as the python script. Any help is appreciated.

Answer 1

In python, when you divide an integer by an integer like 5 / 2, you get 2.5. But in Java, you get 2 because Java treats this kind of division as integer division. In python, you can use // to do integer division.

So lines such as this:

males -= int((P*males)/100)

will yield a different result in Java. To write this correctly in Java, you need to make one of the operands a double, like this:

males -= (int)((P*males)/100.0); // 100.0 is double, 100 is int.

Change all the lines where you have an integer dividing by an integer.

• Peter Filip: I'm running the java code on an online IED. When I change females += (R/2); to females += (R/2.0); the whole thing freezes.
• Sweeper: @PeterFilip try another IDE, ideally one that's on your machine.