# Sehr einfacher Taschenrechner mit Methoden

69061
Niall Szalkai

Ich habe einen grundlegenden Rechner mit Methoden erstellt. Dies ist mein erster Versuch, Methoden zu verwenden, und ich würde gerne sehen, ob ich dies verbessern kann, da sich viel Code wiederholt.

``````import java.util.Scanner;

public class Calculator {

public static void main(String[] args) {

Scanner kb = new Scanner(System.in);

System.out.println("Simple Calculator");

System.out.println("2. Subtraction");
System.out.println("3. Division");
System.out.println("4. Multiplication");

System.out.print("\nWhat would you like to do?: ");
int choice = kb.nextInt();
System.out.println();

if (choice == 1){
}
else if (choice == 2){
subtraction();
}
else if (choice == 3){
division();
}
else if (choice == 4){
multiplication();
}

System.out.println();
kb.close();
}

int nOne, nTwo;
Scanner kb = new Scanner(System.in);

System.out.print("\nFirst Number: ");
nOne = kb.nextInt();

System.out.print("\nSecond Number: ");
nTwo = kb.nextInt();

kb.close();
System.out.println("\nSum: " + nOne + " + " + nTwo + " = " + (nOne + nTwo));
}

public static void subtraction(){
int nOne, nTwo;
Scanner kb = new Scanner(System.in);

System.out.println("Subtraction");

System.out.print("\nFirst Number: ");
nOne = kb.nextInt();

System.out.print("\nSecond Number: ");
nTwo = kb.nextInt();

kb.close();
System.out.println("\nSum: " + nOne + " - " + nTwo + " = " + (nOne - nTwo));
}

public static void division(){
int nOne, nTwo;
Scanner kb = new Scanner(System.in);

System.out.println("Division");

System.out.print("\nFirst Number: ");
nOne = kb.nextInt();

System.out.print("\nSecond Number: ");
nTwo = kb.nextInt();

kb.close();
System.out.println("\nSum: " + nOne + " / " + nTwo + " = " + (nOne / nTwo));
}

public static void multiplication(){
int nOne, nTwo;
Scanner kb = new Scanner(System.in);

System.out.println("Multiplication");

System.out.print("\nFirst Number: ");
nOne = kb.nextInt();

System.out.print("\nSecond Number: ");
nTwo = kb.nextInt();

kb.close();
System.out.println("\nSum: " + nOne + " x " + nTwo + " = " + (nOne * nTwo));
}
}
``````
Wenn Sie sich fragen, warum Sie nicht viele Stimmen erhalten haben, liegt dies daran, dass Sie Ihre Antwort spät am Tag gepostet haben. Niemand hat noch Munition. ;) syb0rg vor 6 Jahren 1
@ Syb0rg Ha! Es ist ok :) Jeder arbeitet hart genug und ich bin mir sicher, dass es in der Zeit gesehen werden wird. Niall Szalkai vor 6 Jahren 1

## 2 Antworten auf die Frage

asteri

Nice job! I hope you find the comments below useful as you progress.

1. Variable names: Try to have variable names which describe what the variable actually represents or holds. For example, I have no idea why you named your `Scanner` "kb".
2. Method names: Method names should always be verb phrases (actions) which describe what the method does. So for example, your `addition()` method might be better named `performAddition()` or some such. Even just `add()` might work, though that might be a bit misleading and lead someone reading your code to believe that all the method does is add two numbers, when really the core functionality is user interface.
3. Redundancy: Any time you are copy-pasting code, alarm bells should go off in your head. You do this in multiple places. Most notable is:

``````System.out.print("\nFirst Number: ");
nOne = kb.nextInt();

System.out.print("\nSecond Number: ");
nTwo = kb.nextInt();
``````

What that means is that this is a prime candidate for encapsulation into its own method. Something like this:

``````private static int[] getNumbers() {
int[] numbers = new int;
System.out.print("\nFirst Number: ")
numbers = scanner.nextInt();
System.out.print("\nSecond Number: ");
numbers = scanner.nextInt();
return numbers;
}
``````

Now we can simply call this method whenever we need to get numbers from the user. Much easier, and we've reduced the complexity of our code.

Another thing that's redundant is your constant re-declaration of `kb = new Scanner(System.in)`. You really only need to do this once. If it were me, I'd have it as a static field for the entire class, e.g.,

``````private static final Scanner STDIN = new Scanner(System.in);
``````

This is the basic rule for how constants are defined in Java. I named the variable `STDIN` because this is a convention for referring to the "standard input" stream, but `SCANNER` or something would be just as good.

Some other small things

You should consider using a `switch` statement on your `choice` variable:

``````switch(choice) {
case 1:
break;
case 2:
performSubtraction();
break;
case 3:
performDivision();
break;
case 4:
performMultiplication();
break;
default:
System.out.println("Invalid choice!");
break;
}
``````

... or you could write it all in-line, if it looks better to you, since each block only really does one thing:

``````switch(choice) {
case 2: performSubtraction(); break;
// etc.
}
``````

This would also be a perfect use-case for enums, but that my be getting a bit too complicated for a starting project.

Small final note: I think you have a bug. The line where you display the results always says "sum", even when you're doing division, multiplication, or subtraction. :)

http://pastebin.com/70wnzARQ - Vielen Dank, ich denke, diese neue Version deckt die meisten Dinge ab, die Sie erwähnt haben :) Niall Szalkai vor 6 Jahren 0
Ich freue mich darauf, neuen Code in diesem Programm zu sehen. Malachi vor 6 Jahren 0
Malachi

Your flow is a little clunky.

If I were going to calculate something I would do it in this order:

`Number1` then `operator` then `Number2`

This way I know what I am doing, especially when playing with division.

I think you should ask for the first number then ask for the operation and then ask for the third number.

Also change your choice to take input of `+`, `-`, `*`, `/` as well as the numbered choices, in doing this you are one step closer to taking this to a new level with forms or whatever direction your application is going to take away from the console.

Eventually you can add something to this so that it distinguishes the operators separately and the user can write an expression rather than answer questions about the expression, I think that is really the goal right?

This sounds like a fun project!

Dies sind wirklich gute Tipps, wenn Sie dieses Taschenrechnerprojekt in Zukunft erweitern möchten, um weiter zu lernen. asteri vor 6 Jahren 1
Ich habe vor, zu versuchen, meinen eigenen Rechner zu erstellen, wenn ich heute nach Hause komme. Malachi vor 6 Jahren 0