Several string inputs for one variable

Question

Is there any other way to shorten this condition?

if (oper.equals("add") || oper.equals("Add") || oper.equals("addition") ||
oper.equals("Addition") || oper.equals("+"))

I was just wondering if there's something I can do to 'shortcut' this. The user will type a string when prompted what kind of operation is to be performed in my simple calculator program. Our professor said our program should accept whether the user enters "add", or "Add", you know, in lowercase letters or not... Or is the only way I should do it?

Answer 1

You can use String#equalsIgnoreCase(String) for 1st four strings: -

if (oper.equalsIgnoreCase("add") || 
    oper.equalsIgnoreCase("addition") || 
    oper.equals("+"))

If number of strings increases, you would be better off with a List, and use its contains method. But just for these inputs, you can follow this approach only.

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Another way to approach this is to use String#matches(String) method, which takes a regex: -

if (oper.matches("add|addition|[+]")

But, you don't really need a regex for this. Specially, this method can become ugly for greater inputs. But, it's just a way for this case. So, you can choose either of them. 1st one is more clear to watch on first go.

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Alternatively, you can also use enum to store operators, and pass it's instance everywhere, rather than a string. It would be more easy to work with. The enum would look like this:

public enum Operator {
    ADD,
    SUB,
    MUL,
    DIV;
}

You can enhance it to your appropriate need. Note that, since you are getting user input, you would first need to identify the appropriate enum instance based on it, and from there-on you can work on that enum instance, rather than String.

Answer 2

In addition to @Rohit's answer, I would like to add this.

In case of comparison of strings, if oper is null a NullPointerException could be thrown. SO its always better to write

"addition".equalsIgnoreCase(oper)

instead of

oper.equalsIgnoreCase("addition")

Answer 3

If aDD is considered as invalid input, you can consider following approach:

ArrayList<String> possibleInputs = new ArrayList<String>();

possibleInputs.add("Add");
possibleInputs.add("add");
possibleInputs.add("Addition");
possibleInputs.add("addition");
possibleInputs.add("+");

if(possibleInputs.contains(oper))
{
    // ...
}