Simple math Java program, if statements not working

Question

I am having trouble getting this program to work properly, it takes 2 numbers then does the type of math you tell it to do. I wrote this just to refresh my memory having not worked with java for a few months. Here is the code:

import java.util.Scanner;
public class math {
    public static void main(String[] args){
        Scanner one = new Scanner(System.in);
        Scanner two = new Scanner(System.in);
        System.out.print("Enter a number: ");
        int n1 = one.nextInt();
        System.out.print("Enter a second number: ");
        int n2 = one.nextInt();
        System.out.print("Add, subtract, multiply, or divide? ");
        String f = two.nextLine();
        System.out.println(f);
        if (f=="add"){
            System.out.println(n1 + n2);
        }else if (f=="subtract") {
            if (n1>n2){
                System.out.println(n1 - n2);
            }else{
                System.out.println(n2 - n1);
            }
        }else if (f=="multiply"){
            System.out.println(n1 * n2);
        }else if (f=="divide"){
            if (n1>n2){
                System.out.println(n1 / n2);
            }else{
                System.out.println(n2 / n1);
            }
        }
    }
}

Edit: Thank you all, it works with f.equals()

String.equals() compares content. == compares locations. For comparing string literals and interned strings, == will work. In all other cases, .equals() is the only option. Basically, .equals() — Ryan Amos
– Ryan Amos, Commented Sep 15, 2012 at 16:03

Jon Lin · Accepted Answer · 2012-09-15 16:01:55Z

3

Your String comparisons need to be changed to use String.equals() instead of ==:

if (f=="add"){

To

if ("add".equals(f)){

and

    }else if (f=="subtract") {

to

    }else if ("subtract".equals(f)) {

etc.

answered Sep 15, 2012 at 16:01

Jon Lin

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2 Comments

WillumMaguire Over a year ago

That worked, thank you. Is there a similar way to test if there is a single character or certain string of text inside of variable f? Such as this: if (f contains the string "enter string here") {do this}

huseyin tugrul buyukisik Over a year ago

f.contains(CharSequence c) :) you can use a string in the place of a charsequence

huseyin tugrul buyukisik · Accepted Answer · 2012-09-15 16:15:34Z

3

if (f=="add")

compares references. You need to

if(f.equals("add"))

because java has many objects and mainly == is used for reference comparing unless you are not doing it for primitives.

If you want to check if it has a string inside,

if(f.contains("asdas"))

edited Sep 15, 2012 at 16:15

answered Sep 15, 2012 at 16:00

huseyin tugrul buyukisik

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Comments

arshajii · Accepted Answer · 2012-09-16 03:55:12Z

You're comparing strings with ==, use f.equals("add") instead (same with other comparisons). Generally, == should only be used on primitive data types as opposed to objects (like Strings).

import java.util.Scanner;
public class math {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        System.out.print("Enter a number: ");
        int n1 = in.nextInt();
        System.out.print("Enter a second number: ");
        int n2 = in.nextInt();
        System.out.print("Add, subtract, multiply, or divide? ");
        String f = in.nextLine();
        System.out.println(f);
        if (f.equals("add")) {
            System.out.println(n1 + n2);
        } else if (f.equals("subtract")) {
            if (n1 > n2){
                System.out.println(n1 - n2);
            } else {
                System.out.println(n2 - n1);
            }
        } else if (f.equals("multiply")) {
            System.out.println(n1 * n2);
        } else if (f.equals("divide")) {
            if (n1>n2) {
                System.out.println(n1 / n2);
            } else {
                System.out.println(n2 / n1);
            }
        }
    }
}

Also, there's no need to use two Scanner instances, one will suffice. Just as a side note, strings have an equalsIgnoreCase method as well which will test for equality but ignore the cases of the characters.

Dylan Black · Accepted Answer · 2015-08-02 00:48:32Z

0

While

f.equals("add");

will work, if I enter Add, it won't work. To fix this you can replace f.equals("word") with

f.equalsIgnoreCase("add");

which allows any case, AdD will work, ADD will work, aDD will work, etc.

Hope this helps!

answered Aug 2, 2015 at 0:48

Dylan Black

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