CalculatorApp.java

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package com.ucoruh.calculator;
 
import org.slf4j.LoggerFactory;
 
import ch.qos.logback.classic.Logger;

public class CalculatorApp {
  private static final Logger logger = (Logger) LoggerFactory.getLogger(CalculatorApp.class);

  static final String USAGE = "Usage: CalculatorApp <number> <+|-|*|/> <number>";
 
  private CalculatorApp() {
    // Utility/entry-point class: not meant to be instantiated.
  }

  public static void main(String[] args) {
    System.out.println(run(args));
  }

  static String run(String[] args) {
    if (args == null || args.length != 3) {
      logger.warn("Expected 3 arguments, got {}", args == null ? 0 : args.length);
      return USAGE;
    }
 
    final int left;
    final int right;
 
    try {
      left = Integer.parseInt(args[0]);
      right = Integer.parseInt(args[2]);
    } catch (NumberFormatException e) {
      logger.error("Invalid operand: {}", e.toString());
      return "Error: operands must be integers. " + USAGE;
    }
 
    String operator = args[1];
    Calculator calculator = new Calculator();
 
    switch (operator) {
      case "+":
        return String.valueOf(calculator.add(left, right));
 
      case "-":
        return String.valueOf(calculator.subtract(left, right));
 
      case "*":
        return String.valueOf(calculator.multiply(left, right));
 
      case "/":
        try {
          return String.valueOf(calculator.divide(left, right));
        } catch (ArithmeticException e) {
          logger.error("Division by zero requested");
          return "Error: division by zero";
        }
 
      default:
        logger.warn("Unknown operator: {}", operator);
        return "Error: unknown operator '" + operator + "'. " + USAGE;
    }
  }
}