Having trouble the .equals in JAVA

Question

package thenewboston;
import java.util.Scanner;
public class apple {
    public static void main(String args[]) {
        Scanner myScan = new Scanner(System.in);
        System.out.println("Enter your first num");
        double fnum, snum, answer;
        String oper;
        fnum = myScan.nextDouble();
        System.out.println("Enter your second num");
        snum = myScan.nextDouble();
        System.out.println("Enter your operation");
        if (oper.equals("+")) {
        answer = fnum + snum;
        } else if (oper.equals("-")){
            answer = fnum - snum;
        } else if (oper.equals("*")) {
            answer = fnum * snum;
        } else if (oper.equals("/")){
            answer = fnum / snum;
        } else {
            System.out.println("Please choose a valid operation");
        }
        System.out.println("Your answer is: " + answer);
    }

}

Hi. Im trying to use .equals() in order to create a basic calculator but there is an error showing up on oper when I write oper.equals("...").

Post your *complete* error messages here please as this is critical information. — Hovercraft Full Of Eels, Apr 05 '15 at 21:25
`"but there is an error showing up "` - The first step in correcting an error is *reading the error message*. — David, Apr 05 '15 at 21:30
possible duplicate of [What is a Null Pointer Exception, and how do I fix it?](http://stackoverflow.com/questions/218384/what-is-a-null-pointer-exception-and-how-do-i-fix-it) — David, Apr 05 '15 at 21:31
@David He would not get an NPE. He would get a compile error. — khelwood, Apr 05 '15 at 21:33

score 0 · Answer 1 · answered Apr 05 '15 at 21:32

0

You should assign value to oper.

String oper = "*";

answered Apr 05 '15 at 21:32

tuğrul altun

131
1
4

ggmathur · Answer 2 · 2015-04-05T21:35:44.577

0

You are probably getting an error because you never actually set oper to anything before using it.

...
snum = myScan.nextDouble();
System.out.println("Enter your operation");
oper = myScan.nextLine(); //<-- You were missing this.
if (oper.equals("+")) {
answer = fnum + snum;
...

edited Apr 05 '15 at 21:35

answered Apr 05 '15 at 21:33

ggmathur

833
5
12

score 0 · Answer 3 · answered Apr 05 '15 at 21:50

0

You didn't ask the user to input an operation, therefore, your oper can't match any of the things you say later.

answered Apr 05 '15 at 21:50

Alan He

1

Having trouble the .equals in JAVA

3 Answers3