Thread: 'else if' jumps to final else.

Explanation below code.

import java.util.Scanner;
 
class apples {
	 public static void main(String[] args) {
		 Scanner input = new Scanner(System.in);
		 double sum;
		 String[] operators = {"plus", "minus", "multiply", "divide"};
 
 
		 System.out.println("Today, we're going to do some maths!");
 
 
		 System.out.println("Please enter your first number:");
		 double num1 = input.nextDouble();
 
		 System.out.println("Please enter your second number:");
		 double num2 = input.nextDouble();
 
 
		 System.out.println("What would you like to do to these numbers? Plus, minus, multiply or divide?");
		 String op = input.nextLine();
 
 
		 if (op.equalsIgnoreCase(operators[0])){
			 sum = num1 + num2;
			 System.out.println(sum);
		 }
		 else if (op.equalsIgnoreCase(operators[1])){
			 sum = num1 - num2;
			 System.out.println(sum);
		 }
		 else if (op.equalsIgnoreCase(operators[2])){
			 sum = num1 * num2;
			 System.out.println(sum);
		 }
		 else if (op.equalsIgnoreCase(operators[2])){
			 sum = num1 / num2;
			 System.out.println(sum);
		 }else {
			 System.out.println("You typed it wrong. Start again!");
		 }
 
 
 
	 }
 
			}

OUTPUT:

Today, we're going to do some maths!
Please enter your first number:
1
Please enter your second number:
2
What would you like to do to these numbers? Plus, minus, multiply or divide?
You typed it wrong. Start again!

As a little practice mess around, since I'm still in the early stages of learning, I decided to made simple a two number calculator. But I'm having a problem with this 'else if' statement. I can't fathom why it appears to completely ignore the 21st line and jump straight to the final 'else':

String op = input.nextLine();

This means that the user then can't choose the desired operator.
Any help would be fantastic, thank you.

Hello!

Firstly, I noticed that your last two else-if statements checked for equality to operators[2], so you might want to change the last one to operators[3].

Secondly, when checking if Strings are equivalent, it is better to use the equals() method. It is pretty simple: String1.equals(String2) returns a boolean, so you can use it in your if-statements.

Finally, I don't know why your...

op = input.nextLine();

...isn't working; perhaps you could try...

op = input.next();

...? Just a suggestion. Otherwise, I don't know. Hopefully this helps!

Originally Posted by snowguy13

Hello!

Firstly, I noticed that your last two else-if statements checked for equality to operators[2], so you might want to change the last one to operators[3].

Secondly, when checking if Strings are equivalent, it is better to use the equals() method. It is pretty simple: String1.equals(String2) returns a boolean, so you can use it in your if-statements.

Finally, I don't know why your...

op = input.nextLine();

...isn't working; perhaps you could try...

op = input.next();

...? Just a suggestion. Otherwise, I don't know. Hopefully this helps!

Ack, that's what I get for being lazy and c+p-ing sections of code. Fixed now.

Is .equals() really all that different from .equalsIgnoreCase()? I used IgnoreCase because it makes more sense from a user end point of view, meaning the person inputting doesn't have to match the case of the String exactly, other than spelling. Does .equalsIgnoreCase() throw up problems sometimes?

I just tried .next(); and it worked! Thank you. I think I'll have to do some reading up on .nextLine() to see why it didn't work. Still a lot more learning to do.

Originally Posted by 2by4

You appear to have a rather careless typing error in your code. Read through it carefully.

Did you mean .next() should be used instead? Because that seems to have worked now.

Is .equals() really all that different from .equalsIgnoreCase()?

I apologize; somehow I missed that. Yes, equalsIgnoreCase() will work fine and shouldn't cause any problems. Sorry.

I just tried .next(); and it worked!

That's great! I'm really not sure why nextLine() didn't work where next() did... Strange. But I'm glad you figured out your code!

which snowguy13 encouraged

Firstly, I don't think that copying and pasting is a problem. Example: this morning I was rearranging the way a KeyListener was organized and using code from already developed MouseListeners so that the KeyListener would do the same thing as the MouseListeners. Why would I want to retype all the code for the KeyListener when it's already there for the MouseListeners? I don't think that copying and pasting does too much harm, as long as one keeps careful track of what he/she is copying and pasting.

Secondly, if it is a problem, how am I encouraging it by bringing the error to the coder's attention?

I'd just like to point out, when I said I'd copied and pasted the code I meant I'd typed

 else if (op.equalsIgnoreCase(operators[2]))

I copied and pasted it the relevant amount of times, somehow ending up with me accidentally putting index [2] twice. I didn't copy and paste it from anywhere, that'd defeat the object of me trying to learn.
I would've no doubt noticed it once I had gotten past the problem of the .nextLine().

(and perhaps I was being a little tongue-in-cheek in saying you encouraged him)

No, I have a nasty habit of overreacting to little things like that. I'm the one at fault and you were right to call me out. For that, I'm sorry!

I would've no doubt noticed it once I had gotten past the problem of the .nextLine().

There's no doubt you would have. Just make sure to be careful in the future if you ever start doing large projects with multiple classes or large methods, as this problem can turn nasty quite rapidly if you're not careful.