Exceptions

Question 1

Happy Path

Answer 1

The path through the code where exceptions are not thrown

Question 2

Runtime Exception

Answer 2

Tend to be unexpected, but not necessarily fatal.

Also called unchecked exceptions.

Includes RuntimeException and all its subclasses

Question 3

Checked Exception

Answer 3

Includes Exception and all subclasses that do not extend RuntimeException

Question 4

Handle or Declare Rule

Answer 4

A rule enforced by the compiler that states if a statement throws a checked exception, it must attempt to catch the exception or declare the exception in the method declaration using the throws keyword.

Question 5

throws

Answer 5

Indicates that the code might throw the specified exception, but it might not

Question 6

For Runtime Exception…

1) How to recognize?
2) Okay for program to catch?
3) Is program required to handle or declare?

Answer 6

1) Subclass of RuntimeException
2) Yes
3) No

Question 7

For Checked Exception…

1) How to recognize?
2) Okay for program to catch?
3) Is program required to handle or declare?

Answer 7

1) Subclass of Exception but not subclass of RuntimeException
2) Yes
3) Yes

Question 8

For Error…

1) How to recognize?
2) Okay for program to catch?
3) Is program required to handle or declare?

Answer 8

1) Subclass of Error
2) No
3) No

Question 9

try statement syntax

Answer 9

try {
   //code
} catch (exception_type e) {
   //code
}

must have the braces!

Question 10

What must go along with a try block?

Answer 10

Either a catch block or a finally block.

Note: You don’t need both! You can even just have a try and finally with no catch. You can also have multiple catch blocks

Question 11

If there are multiple catch blocks, you must watch out for….

Answer 11

Superclasses being handled before subclasses.

For example, every exception class extends from the class Exception, so if you were to catch an Exception before any others, then the catch statements would be unreachable and the compiler would say no no

Question 12

ArithmeticException

Answer 12

Thrown by the JVM when code attempts to divide by 0

RuntimeException

Question 13

ArrayIndexOutOfBoundsException

Answer 13

Thrown by the JVM when code uses an illegal index to access an array

RuntimeException

Question 14

ClassCastException

Answer 14

Thrown by the JVM when an attempt is made to cast something to a subclass of which it is not an instance

RuntimeException

String type = “moose”;
Integer number = (Integer) type; // DOES NOT COMPILE
More complicated code thwarts Java’s attempts to protect you. When the cast fails at runtime, Java will throw a ClassCastException:

String type = “moose”;
Object obj = type;
Integer number = (Integer) obj;
The compiler sees a cast from Object to Integer. This could be okay. The compiler doesn’t realize there’s a String in that Object.

Question 15

IllegalArgumentException

Answer 15

Thrown by the programmer to indicate that a method has been passed an illegal or inappropriate argument

Checked Exception

Question 16

NullPointerException

Answer 16

Thrown by the JVM when there is a null reference where an object is required

RuntimeException

Question 17

NumberFormatException

Answer 17

Thrown by the programmer when an attempt is made to convert a String to a numeric type but the String doesn’t have an appropriate format

Question 18

FileNotFoundException

Answer 18

Thrown programmatically when code tries to reference a file that does not exist.

Checked Exception

Question 19

IOException

Answer 19

Thrown programmatically when there’s a problem reading or writing a file

Checked Exception

Question 20

ExceptionInInitializerError

Answer 20

Thrown by the JVM when a static initializer throws an exception and doesn’t handle it

Question 21

StackOverflowError

Answer 21

Thrown by the JVM when a method calls itself too many times

Question 22

NoClassDefFoundError

Answer 22

Thrown by the JVM when a class that the code uses is available at compile time but not at runtime

Question 23

3 ways to print an exception called e

Answer 23

System.out.println(e);
System.out.println(e.getMessage());
e.printStackTrace();