Defensive Programming

public class Main {
  static int divide(int a, int b) {
    if (b == 0) {
      throw new IllegalArgumentException("Denominator must not be zero");
    }
    return a / b;
  }
  public static void main(String[] args) {
    try {
      System.out.println(divide(10, 0));
    } catch (IllegalArgumentException e) {
      System.out.println("Caught: " + e.getMessage());
    }
  }
}

public class Main {
  static String upper(String s) {
    if (s == null) {
      throw new IllegalArgumentException("String must not be null");
    }
    return s.toUpperCase();
  }
  public static void main(String[] args) {
    try {
      System.out.println(upper(null));
    } catch (IllegalArgumentException e) {
      System.out.println("Caught: " + e.getMessage());
    }
  }
}

public class Main {
  static int[] makeArray(int size) {
    if (size < 0) {
      throw new IllegalArgumentException("Size must be non-negative");
    }
    return new int[size];
  }
  public static void main(String[] args) {
    try {
      makeArray(-5);
    } catch (IllegalArgumentException e) {
      System.out.println("Caught: " + e.getMessage());
    }
  }
}