Java Exception Handling Quiz

Exception Handling Overview

• Exception handling is a mechanism to manage runtime errors.
• Runtime errors cause a program to terminate abnormally.
• Exception handling allows a program to continue running or terminate gracefully after a runtime error.

Show Runtime Error Example

• A program example demonstrates what happens when a division by zero error occurs
• The program terminates with an error message.

Fix It Using an If Statement

• An example shows how to use an if statement to prevent division by zero
• The if statement checks if the divisor is not zero before performing the division.

With a Method

• A method can be used to encapsulate the division operation.
• The method can check for the divisor being zero, and terminate if it is.
• Use System.exit(1) to indicate an error exit.
• System.exit(0) indicates a successful exit.

Exception Advantages

• Exception handling helps a method throw an exception to the caller.
• This is useful to handle exceptions in a calling method instead of the method that caused it.

Handling InputMismatch Exception

• The InputMismatchException example shows how to continuously prompt a user for a valid input until the input is correct.
• The program will continue reading an input until a valid integer is entered.

Exception Types

• Exceptions are objects with defined classes.
• The root class of exceptions is java.lang.Throwable.
• Throwable branches into Exception and Error.
• Error represents internal system errors.
• Exception branches into classes like RuntimeException and IOException.
• IOException represents errors during input/output operations.

System Errors

• System errors are represented by Error class.
• System errors are often not recoverable.

Runtime Exceptions

• RuntimeException is caused by programming mistakes.
• Examples are ArrayIndexOutOfBoundsException, NullPointerException, ArithmeticException, etc.

Checked Exceptions vs. Unchecked Exceptions

• RuntimeException, Error and subclasses are unchecked exceptions
• All other exceptions are checked exceptions

Unchecked Exceptions

• Unchecked exception errors are generally programming logic errors.
• Examples are NullPointerException and ArrayIndexOutOfBounds.
• Java does permit these exceptions to potentially occur without a try/catch block.

Declaring, Throwing and Catching Exceptions

• Java's exception handling uses three methods:
• declare an exception
• throw an exception
• catch an exception

Declaring Exceptions

• Checked exceptions must be declared in method signatures.
• Failure to correctly declare a checked exception results in compiler errors.

Throwing Exceptions

• A program creates an exception instance when an error is detected.
• The exception object is then thrown.

Catching Exceptions

• A try block contains statements that might throw an exception.
• A catch block handles potential exceptions, processing any caught exceptions.

The finally Clause

• The finally block ensures code execution regardless of exceptions.
• It ensures cleanup code (e.g., closing files, releasing resources) runs.

Trace a Program Execution

• Java's exception handling is described with a flowchart.
• The program executes statements in the try block.
• If an exception occurs, the corresponding catch block is executed.
• The finally block runs after the try-catch block.

Catch or Declare Checked Exceptions

• Checked exceptions require either a try block (and catch block) or by declaring the exception using throws clause in method signature.

Example (Declaring, Throwing, and Catching Exceptions)

• A specific example about declaring and catching Exceptions by creating class CircleWithException and InvalidRadiusException

Cautions When Using Exceptions

• Exception handling can potentially reduce program efficiency

When to Use Exceptions

• Use exceptions for unexpected or unrecoverable failures.
• Don't use exceptions for simple or expected errors.