Chapter 6: exceptions

Question 1

A(n) ____ exception happens during runtime.

Answer 1

unchecked

Question 2

What’s the difference between an exception and compiler error?

Answer 2

All exceptions happen at runtime. Compiler error happens before the program is run.

Question 3

A runtime exception is also known as:

Answer 3

unchecked exception

Question 4

A _____ exception inclucdes Exception and all subclassed that do not extend Runtime Exception

Answer 4

checked exception

Question 5

Is this a checked or unchecked exception?

void fall() throws Exception{

throw new Exception();

}

Answer 5

Checked. Because we tell the program how to handle the exception be declaring.

Question 6

What does the ‘throw’ keyword indicate when used in a program?

Answer 6

Just that this method might throw an exception

Question 7

Is the NullPointerException checked or unchecked?

Answer 7

unchecked. We didn’t tell the program what to do and it happened at runtime.

Question 8

How do you recognize a Runtime exception? What will it’s super class be?

Answer 8

RuntimeException

Question 9

Does Java force you to explicit handle a runtime exception with something like a throws() or try catch?

Answer 9

No

Question 10

How do you recognize a checked exception? What will it’s super class be?

Answer 10

It will be a subclass of Exception but not of RuntimeException.

Question 11

Does Java force you to handle or declare a checked exception?

Answer 11

yes

Question 12

How do you recognize an error exception? What will it’s superclass be?

Answer 12

Subclass of Error

Question 13

Will the program catch an Error (are errors fatal?), and are you required to handle or declare an exception to handle an Error.

Answer 13

Errors are fatal. Errors are not declared.

Question 14

What does Java use ‘try’ statements for?

Answer 14

To separate the logic that might throw an exception from the logic to handle that exception.

Question 15

Are curly braces required in a try catch statement?

Answer 15

Yes.

Question 16

What happens to the catch block of code if the code in the try block doesn’t fail?

Answer 16

It doesn’t run.

Question 17

Are the curly braces in a try catch required around both the try block and the catch clause?

Answer 17

Yes

Question 18

Why doesn’t this compile?

try

fall();

catch(Exceptione e)

System.out.print(“Get up”);

Answer 18

No. the try block requires curly braces

Question 19

Does this compile?

try{

fall();

}

Answer 19

No. You must have a catch statement in a try/catch block.

Question 20

When does the finally{} clause execute?

Answer 20

The finally clause executes no matter what in a try catch statement. If the try is successful, the finally still runs. If the try is unsuccessful and the catch clause runs, the finally block will still run.

Question 21

Does finally have to follow a catch statement in a try catch block?

Answer 21

yes. if the catch doesn’t precede the finally the code will not compile.

Question 22

Are you allowed to have multiple catch statements in a try/catch?

Answer 22

Yes.

Question 23

Let’s say you have a try catch block with custom exceptions. Or, at least you are using different kinds of exceptions, some of which inherit from another. What happens if you run a subclass exception that runs before an exception using a superclass of that subclass as the exception.

Answer 23

This is just fine. As long as the subclass exception runs before the super this will be fine. but if the super runs before the sub, the compiler will indicate that some code is out of reach.

Question 24

Remember, at most one catch block will run and it will be the first catch block that can handle it.

Question 25

Which three types of exceptions do you need to be able to recognize for the OCA exam?

Answer 25

Runtime (unchecked) exceptions, check exceptions, and errors.

Question 26

Do runtime exceptions have to be handled or declared?

Answer 26

No

Question 27

Can runtime exceptions be thrown by both the programmer and the jvm?

Answer 27

yes

Question 28

Why would ArithmeticException be thrown?

Answer 28

Thrown by the JVM when the code attempts to divide by zero

Question 29

What causes an ArrayIndexOutofBoundsException to be thrown?

Answer 29

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

Question 30

Why would a ClassCastException be thrown?

Answer 30

This is thrown by the JVM when an attempt is made to cast an object to a subclass of which it is not an instance.

Question 31

Why would an IllegalArgumentException be thrown?

Answer 31

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

Question 32

What causes a NullPointerException?

Answer 32

This is thrown by the JVM when there is a null reference where an object is required.

Question 33

Why would a NumberFormatException be thrown?

Answer 33

This is thrown by the programmer when an attempt is made to convert a string to a numeric type but the string doesn’t have the appropriate format.

Question 34

Which exception would be thrown?

int answer = 11/0;

Answer 34

ArithmeticException

Question 35

Which exception would be thrown by this code?

int[] countsOfMoose = new int[3];

System.out.println(counstOfMoose[-1]);

Answer 35

ArrayIndexOutofBoundsException

Question 36

Which exception would be thrown by the code?

String type = “moose”;

Integer number = (Integer) type;

Answer 36

ClassCastException

Question 37

Which exception would be thrown by this code?

String name;

public void printLength() {

System.out.println(name.length());

}

Answer 37

NullPointerException. name doesn’t have a value (other than null) so it cannot print out a length.

Question 38

Which exception would be thrown by this code?

Integer.parseInt(“abc”);

Answer 38

NumberFormatException

Question 39

Checked exceptions have Exception in their hierarchy but not _____

Answer 39

RuntimeException

Question 40

Checked exceptions must be ____ or _____.

Answer 40

Handled or declared

Question 41

Checked exceptions can be thrown by the _____ or the _____.

Answer 41

Checked exceptions can be thrown by the programmer or the jvm.

Question 42

Which checked exception is thrown when code tries to reference a file that does not exist?

Answer 42

FileNotFoundException

Question 43

Which exception is thrown programmatically when there’s a problem reading or writing a file?

Answer 43

IOException

Question 44

FileNotFoundException is a child of ______

Answer 44

IOException

Question 45

Errors extend the ____ class

Answer 45

Errors

Question 46

Errors are thrown by the _____ and should not be _____ or ______.

Answer 46

Jvm. Handled or declared

Question 47

Which error is thrown by the JVM when a static initializer throws an exception and doesn’t handle it?

Answer 47

ExceptionInInitializerError

Question 48

Which error is thrown by infinite recursion?

Answer 48

StackOverflowError

Question 49

Which error is thrown by the JVM when a class that the code uses is available at compile time but not at runtime?

Answer 49

NoclassDefFoundError

Question 50

Java runs ____ initializers the first time a class is used.

Answer 50

Static initializers

Question 51

Which two exceptions will this code throw?

static { int[] countsOfMoose = new int{3};

int num = countsOfMoose[-1];

}

public static void main(String[] args){}

Answer 51

ExceptionInInitializerError caused by ArrayIndexOutofBoundsException

Question 52

Which exception will this code throw?

public static void whatever(int num){

whatever(1);

}

Answer 52

StackOverFlowError as this is infinite recursion

Question 53

Why doesn’t this compile?

class CanNotHopException extends Exception{}

class Hopper{public void hop(){}}

class Bunny extends Hopper{

public void hop() throws CanNotHopException{}

}

Answer 53

Because Hopper doesn’t extend the CanNotHopException class. A class isn’t allowed to throw any checked exceptions unless the superclass declares them

Question 54

Why wont this compile?

public static void main(String… strings) {

int[] numbers = {1,2,34};

int[] moreNumbers = new int[] {123,4,5,6};

int[] arraySize = new int[4];

try {

System.out.println(numbers[-1]);

} catch (Exception e ){

e.printStackTrace();

} catch (ArrayIndexOutOfBoundsException e1) {

e1.printStackTrace();

}

}

Answer 54

Exception is the super class of ArrayIndexOutOfBoundsException, so if Exception is run, then the second code becomes unreachable. Java will find the first exception that will work. In this case the super will catch the problem.