Handling Exceptions in Java - ilya-khadykin/notes-outdated GitHub Wiki

Types of exceptions

Exception type	Comment
java.lang.Error	exception in JVM itself (should not be handled by programmer)
java.lang.Exception	checked exceptions in user`s code
java.lang.RuntimeException	unchecked exception in user`s code

• checked exceptions should be always handled by programmer, Java enforces that.
• unchecked exceptions (sub classes from java.lang.RuntimeException (java.lang.NullPointerException, java.lang.ArrayIndexOutOfBoundsException, java.lang.ArithmeticException) are not suppose to be handled and programmer not force to handle them in his\her code.

Custom Exception

public class CalculatorException extends RuntimeException {
  public CalculatorException(String message) {
      super(message);
  }

  public CalcualtorException(String message, Throwable cause) {
     super(message, cause);
  }
}

public class CalculatorImpl implements Calculator {
  
  @Override
  public double calculate(String expr) {
     // Since it's derived from RuntimeException is can't be left unchecked
     throw new CalculatorException("Unsupported operator found");
    //...
  }
}

Handling Exceptions

try {
  //
} catch (TypeOfException ex) {
  // log the error
  System.err.println("An Error occurred");
}

References

1. Java Programming Basics by Simon Roberts