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Rooted by: Make a simple calculator
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  • Code 
    interface Calculator {
  static int calculate(int a, int b, char operation) {
    int result = 0;
    switch(operation) {
        case '+':
        result = a + b; break;
        case '-':
        result = a - b; break;
        case '*':
        result = a * b; break;
        default:
        System.exit(0); break;
    }
    return result;
  }
}
    Test Cases 
    import static java.util.concurrent.ThreadLocalRandom.current;
import static org.junit.jupiter.api.Assertions.assertEquals;

import org.junit.jupiter.api.Test;

class CalculatorTest {
  @Test
  void sample() {
    assertEquals(9, Calculator.calculate(4, 5, '+'));
    assertEquals(7, Calculator.calculate(12, 5, '-'));
    assertEquals(60, Calculator.calculate(20, 3, '*'));
  }

  @Test
  void random() {
    for (int i = 0; i < 100; i++) {
      var pair = current().ints(2, -1000, 1000).toArray();
      assertEquals(pair[0] + pair[1], Calculator.calculate(pair[0], pair[1], '+'));
      assertEquals(pair[0] - pair[1], Calculator.calculate(pair[0], pair[1], '-'));
      assertEquals(pair[0] * pair[1], Calculator.calculate(pair[0], pair[1], '*'));
    }
  }
}
    View Run Output
  • Code
    • import javax.script.ScriptEngineManager;
    • interface Calculator {
    • static int calculate(int a, int b, char operation) {
    • var engine = new ScriptEngineManager().getEngineByName("JavaScript");
    • try {
    • return Integer.parseInt(String.valueOf(engine.eval(a + " " + operation + " " + b)));
    • } catch (Exception cause) {
    • return 0;
    • int result = 0;
    • switch(operation) {
    • case '+':
    • result = a + b; break;
    • case '-':
    • result = a - b; break;
    • case '*':
    • result = a * b; break;
    • default:
    • System.exit(0); break;
    • }
    • return result;
    • }
    • }