exception handling

Question 1

What is an exception?

Answer 1

An exception is an error or unexpected situation that happens while the program is running.

Question 2

What are the common causes of exception?

Answer 2

• User enters the wrong data type
• Dividing a number by zero
• Accessing an array index that doesn’t exist

Question 3

Why are these errors called “exceptions”?

Answer 3

They are unusual cases, not expected during normal program flow.

Question 4

What is exception handling?

Answer 4

Techniques Java uses to detect, handle, and respond to errors in a controlled way using OOP concepts.

Question 5

What are the two main types of exceptions in java?

Answer 5

1. Unchecked Exceptions: come form the Error class or the RunTimeException class
2. Checked Exceptions: are expected errors that the programmer should prepare for. They descend from the Exception class.

Question 6

What are the types of errors?

Answer 6

1. Runtime error
2. Syntax error

Question 7

What is the difference between runtime errors and syntax errors?

Answer 7

• Runtime errors: Happen while the program is running
• Syntax errors: Mistakes in code structure, found before running (during compilation)

Question 8

If your method might throw a checked exception, you must do one of the following:

Answer 8

• Catch it using a try…catch block inside the method

OR

• Declare it using a throws clause in the method header

Question 9

What are the two main classes Java uses to handle errors?

Answer 9

Exception and Error (both from Throwable, which extends Object).

Question 10

What is the Error class?

Answer 10

Represents serious system-level problems (e.g., out of memory). Programmers usually do not handle these.

Question 11

What is the Exception class?

Answer 11

Represents less serious, recoverable problems (e.g., invalid array index). Programmers can handle these using try, catch, and finally.

Question 12

What happens when an exception occurs in Java?

Answer 12

Java throws an Exception and displays an error message.

Question 13

What happens with integer division by zero?

Answer 13

Throws ArithmeticException and causes a crash.

Question 14

What happens with floating-point division by zero?

Answer 14

Result is Infinity.

Question 15

How many categories of exceptions does Java recognize?

Answer 15

Over 75, with names like ActivationException, AlreadyBoundException, AWTException, etc.

Question 16

What is a crash in programming?

Answer 16

The program stops running suddenly due to an error.

Question 17

What is a stack trace?

Answer 17

A list of method calls that led to the error, shown in the error message.

Question 18

Should you always handle exceptions?

Answer 18

Not always, but letting a program crash is not ideal, especially for important programs.

Question 19

How does exception handling improve programs?

Answer 19

Allows catching errors, giving useful messages, and continuing or safely stopping the program.

Question 20

How did programmers prevent errors before exception handling?

Answer 20

Using if-statements to avoid errors (e.g., checking denominator before division).

Question 21

What are the limitations of old-school error prevention?

Answer 21

Can’t prevent all errors (e.g., entering a string instead of a number).

Question 22

What are the advantages of OOP exception handling?

Answer 22

Better error detection, response, and recovery.

Question 23

What is a fault-tolerant program?

Answer 23

Keeps running even if something goes wrong, possibly with reduced features.

Question 24

What is a robust program?

Answer 24

Can handle unexpected problems and is reliable under stress or errors.

Question 25

How does exception handling help?

Answer 25

Makes programs safer, smarter, and more user-friendly.

Question 26

What happens when an exception is thrown in a try block?

Answer 26

Java looks for a matching catch block and executes it if found.

Question 27

What does the getMessage() method do?

Answer 27

Retrieves Java’s built-in message about the exception.

Question 28

Can you fix problems in the catch block?

Answer 28

Yes, you can add code to fix the problem (e.g., change division by 0 to division by 1).

Question 29

How can try blocks help with user input?

Answer 29

Prevent crashes from incorrect input (e.g., entering a letter instead of a number).

Question 30

What happens if an exception occurs during input?

Answer 30

The program can catch the exception and handle it, allowing the user to continue.

Question 31

How can you allow users to continue entering data after an exception?

Answer 31

By handling each input separately and using nextLine() to clear the input buffer.

Question 32

What happens if you declare a variable inside a try block?

Answer 32

It is local to that block and not accessible outside.

Question 33

What problem occurs if a variable is only initialized inside a try block?

Answer 33

If an exception occurs, the variable may remain uninitialized, causing a compile error.

Question 34

How can you ensure a variable always has a value?

Answer 34

- Assign a default value before the try block - Assign a value in the catch block

Question 35

Can you catch more than one type of exception in a try block?

Answer 35

Yes, by using multiple catch blocks.

Question 36

What happens if multiple exceptions could occur in a try block?

Answer 36

Only the first exception is caught; the rest of the try block is skipped.

Question 37

What is upcasting in exception handling?

Answer 37

Handling multiple specific exceptions with a single general Exception catch block.

Question 38

What is the best practice for multiple catch blocks?

Answer 38

Place specific exceptions first, then the general one last.

Question 39

What is a finally block?

Answer 39

Code that always runs, whether or not an exception occurs, usually for cleanup tasks.

Question 40

Where is the finally block placed?

Answer 40

After the try and catch blocks.

Question 41

Why use finally?

Answer 41

Ensures important code (like closing files or releasing resources) always runs.

Question 42

When might code after catch not run?

Answer 42

- No matching catch block (program crashes) - System.exit() is called in try or catch

Question 43

Does finally always run?

Answer 43

Yes, except when System.exit() is called.

Question 44

How do you specify which exceptions a method can throw?

Answer 44

Using the 'throws' keyword in the method signature.

Question 45

Can you create your own exception classes in Java?

Answer 45

Yes, by extending the Exception class.

Question 46

What is Exception Specififcation?

Answer 46

Refers to the way a Java method declares which exceptions it might throw during its execution.

Question 47

What happens if the program tries to divide a number by zero?

Answer 47

An ArithmeticException is thrown.

Question 48

What happens if the program accesses an array index that doesn’t exist?

Answer 48

ArrayIndexOutOfBoundsException is thrown.

Question 49

What is the purpose of the try block?

Answer 49

To enclose code that might throw an exception.

Question 50

What is the purpose of the catch block?

Answer 50

To handle an exception that was thrown in the try block.

Question 51

If a user enters a letter instead of a number when the code expects an integer, what happens?

Answer 51

An InputMismatchException is thrown.

Question 52

throws Doesn’t Mean an Error Will Happen

Answer 52

- Adding throws ExceptionType doesn’t mean the method will always throw an error. - It only warns other programmers: “This method might throw an exception.”

Question 53

To Properly Use a Method, Know These 3 Things:

Answer 53

1.The return type 2. The types and number of arguments it accepts 3.The exceptions it might throw