Exceptions and Assertions

Question 1

ArithmeticException

Answer 1

Thrown when code attempts to divide by 0

Unchecked

Question 2

ClassCastException

Answer 2

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

Unchecked

Question 3

NumberFormatException

Answer 3

Thrown by the program when an attempt is made to convert a string to a numeric type, but the string doesn’t have an appropriate format.

Unchecked

Question 4

java.text.ParseException

Answer 4

Signals that an error has been reached unexpectedly while parsing.

Checked

Question 5

Any exception starting with java.io

Answer 5

deals with IO problems

Checked

Question 6

Any exception starting with java.sql

Answer 6

deals with sql database problems

Checked

Question 7

java.lang.ArrayStoreException

Answer 7

Trying to store the wrong data type in an array.

Unchecked

Question 8

java.time.DateTimeException

Answer 8

Receiving an invalid format string for a date.

Unchecked

Question 9

java.util.MissingResourceException

Answer 9

Trying to access a key or resource bundle that does not exist.

Unchecked

Question 10

java. lang.IllegalStateException

java. lang. UnsupportedOperationException

Answer 10

Attempting to run an invalid operation in collections and concurrency.

Unchecked

Question 11

How to create your own checked exception

Answer 11

class myException extends Exception {}

Question 12

How to create your own unchecked exception

Answer 12

class myException extends RuntimeException {}

Question 13

What are the three common constructors you can use for your custom exception?

Answer 13

public class myException extends Exception {   
   public myException() {
       super(); 
   }

   public myException(Exception e) { 
      super(e);
   }

   public myException(String message) {
      super(message); 
   }
}

Question 14

How to give the option to catch multiple exceptions in the same catch statement

Answer 14

Separate the different exception names by |

catch (DateTimeParseException | IOException e)

Question 15

What is wrong with this catch statement?

catch (FileNotFoundException | IOException e)

Answer 15

FileNotFoundException is a subclass of IOException, and java will not allow this because it is redundant

Question 16

What is wrong with this?

try {
    throw new IOException();
} catch(IOException | RuntimeException e) {
    e = new RuntimeException(); 
}

Answer 16

When using multi-catch, you cannot reassign the exception variable to something new

Note: you can do that when not using multi-catch

Question 17

When can you specify to catch a checked exception in a try block?

Answer 17

Only when it is possible for the exception to be thrown by the code, otherwise it won’t compile.

Question 18

Why would you want to use a try-with-resources statement?

Answer 18

It automatically closes all resources opened in the try clause.

public void newApproach(Path path1, Path path2) throws IOException { 
     try (BufferedReader in =  Files.newBufferedReader(path1);
BufferedWriter out = Files.newBufferedWriter(path2)) {
     out.write(in.readLine()); 
}
}

Question 19

Are catch and finally blocks required when writing a try with resources statement?

Answer 19

No

There is an implicit finally statement to close the resources, but you can also implement your own catch and finally blocks if you want.

Note: The implicit finally block runs before any explicitly coded catch or finally blocks, making the resources no longer available in those blocks!

Question 20

What is wrong with this?

try (Scanner s = new Scanner(System.in)) {  
    s.nextLine();
} catch(Exception e) {
    s.nextInt(); 
} finally{
    s.nextInt();
}

Answer 20

s has been closed by the implicit finally block so it is no longer in the scope of the catch and finally block that are coded.

Question 21

What interface must a class implement in order to be declared in a try-with-resources clause? What is the method that must be implemented?

Answer 21

AutoCloseable

close()

Question 22

Can close() throw Exception?

Answer 22

Yes, but it is recommended to throw something more specific.

And be sure that if it does, then it is handled in the calling method!

Question 23

What method does a try-with-resources statement automatically run after the try block?

Answer 23

close()

The method in the interface AutoCloseable

Question 24

What is a suppressed exception?

Answer 24

When multiple exceptions are thrown before the catch/finally blocks of a try-with-resources statement, there is one primary exception and the rest are stored.

You can loop through the suppressed exceptions like this:

for (Throwable t: e.getSuppressed())

Question 25

Which exception is thrown first at the end of this try block?

try (JammedTurkeyCage t1 = new JammedTurkeyCage(); JammedTurkeyCage t2 = new JammedTurkeyCage())

Answer 25

The exception that calling close() on t2 produces.

The exceptions stack up.

Question 26

Assertion

Answer 26

A Boolean expression that you place at a point in your code where you expect something to be true.

Question 27

Two forms of assert statement

Answer 27

assert boolean_expression;
assert boolean_expression: error_message;

The boolean expression must evaluate to true or false. It can be inside optional paren- thesis. The optional error message is a String

Question 28

What happens if an assertion is false?

Answer 28

Java throws an AssertionError and the program is ended

Question 29

How to enable assertions

Answer 29

java -enableassertions Rectangle

You can also use the shortcut -ea flag:
java -ea Rectangle

By default, this enables assertions in all classes but system classes (built in java classes)

Question 30

How to enable assertions in a specific package/subpackages

Answer 30

java -ea:package_name…

Can also do for specific class

java -ea:package_name.class_name

Question 31

What is the flag for disabling assertions?

Answer 31

-da

Can use all usual variations like when enabling

Question 32

How many catch statements can be run?

Answer 32

Only one

Even if that one throws a new exception

Question 33

Closeable

Answer 33

The interface that was used before AutoCloseable existed.

It has two key requirements:

1) Closeable restricts the type of exception thrown to IOException.
2) Closeable requires implementations to be idempotent (can be called multiple times without any side effects or undesirable behavior on subsequent runs.)