整数/双重交互的意外结果-除法运算后返回零

Question

I have an issue with the "documentLength" variable. When i input the paramenter into the method, it is 93. But for some reason it changes. The input parameter is also an int variable.

I call the class Word, and the method inside it occupationOfDocument from the class checkWord in main like this:

double occupation = word.get(1).occupationOfDocument(documentLength); // line 83 in run-time below

occupationOfDocument looks like this

public double occupationOfDocument(int documentLength){
    int length = getLength(); //equals 8 when I run the program
    int occurances = getOccurances(); //equals 3 when I run the program
    System.out.println(documentLength); //Prints 93 as expected

    double occupation = ((length * occurances)/documentLength)*100; //equals 0 somehow (probably division by)

    return occupation; //expected around 25.8
}

This method returns "0", but if I change the code to this,

private int documentLength = 0;
public double occupationOfDocument(int documentLength){
    int length = getLength(); //equals 8 when I run the program
    int occurances = getOccurances(); //equals 3 when I run the program
    documentLength = this.documentLength;
    System.out.println(documentLength); //Prints 0 somehow

    double occupation = ((length * occurances)/documentLength)*100; //equals 0 somehow (probably divisjon by 0)

    return occupation; //expected around 25.8
}

I get the following RUN-TIME-error:

 Exception in thread "main" java.lang.ArithmeticException: / by zero at Word.occupationOfDocument(Word.java:44) at checkWord.main(checkWord.java:83) 

Word.java:44 This is the line with math, where i declare and initialize occupation

I understand that it says I am dividing by 0. I just don't understand how it happens.

If i input a number instead of the variable "documentLength", the script does as expected

Thanks for helping ;)

IT student in need of help

Answer 1

public double occupationOfDocument(int documentLength){
  int length = getLength(); //equals 8 when I run the program
  int occurances = getOccurances(); //equals 3 when I run the program
  System.out.println(documentLength); //Prints 93 as expected

  double occupation = ((length * occurances)/documentLength)*100; //equals 0 somehow (probably division by)

  return occupation; //expected around 25.8

}

Here, you have multiplied 8 by 3 and gotten 24, then you did integer division by 93 - and that gives you 0.

If you modify the line

double occupation = ((double) (length * occurances)/documentLength)*100; 

that will produce the appropriate result. Learn more about type conversion and type widening to get more context.

Answer 2

You are doing integer division in the first scenario, that means for example 4/3 = 1 and in your case 24/93 = 0 if you want to get it as a double you need to add a cast to the int values:

double occupation = (((double)(length * occurances))/((double)documentLength))*100;

Should be safe. As for the second error you explicitly tell the program to

documentLength = this.documentLength; //this.documentLength = 0 as you defined above

double occupation = ((length * occurances)/documentLength)*100;