Ch16 Exceptions, Assertions, and Localization

Question 1

What is an assertion?

Answer 1

An assertion is a boolean expression that you can place at a point in your code where you expect something to be true.

Question 2

What is an assert statement?

Answer 2

An assert statement is used to declare an expected boolean condition in a program. If the program is running with assertions enabled, then the condition is checked at runtime. If the condition is false, the Java runtime system throws an AssertionError .

Question 3

What is the syntax of an assert statement?

Answer 3

assert keyword
boolean expression
optional message
example:

assert 1 == age;
assert(2 == height);
assert 100.0 == length : “Problem with length”;

Question 4

Is the following assert statement valid?

assert (“Cecilia”.equals(name)): “Failed to verify user data”;

Answer 4

Yes.

Question 5

Is the following assert statement valid?

assert (1);

Answer 5

No. it expects a boolean value.

Question 6

Is the following assert statement valid?

assert x -> true;

Answer 6

No. it expects a boolean value.

Question 7

Is the following assert statement valid?

assert.test(5 > age);

Answer 7

No. The syntax is invalid

Question 8

What happens when assertions are enabled and the boolean expression of an assertion is false?

Answer 8

Java will throw an AssertionError.

Question 9

How can we enable assertions using the java command?

Answer 9

// single-file source-code

java -ea SomeFile.java
java -enableassertions SomeFile.java
// normal

java -ea SomeFile
java -enableassertions SomeFile

Question 10

Given the package com.demos, how do we run the application and only enable assertions for that package?

Answer 10

• java -ea:com.demos… MyMainClass
• With one argument ending in “…”, assertions are enabled in the specified package and any subpackages by default.
• With one argument not ending in “…”, assertions are enabled in the specified class.

Question 11

What flag can we use to exclude a package/class from enabling assertions?

Answer 11

-da or -disableassertions

Question 12

Given the class Test in package com.demos, how do we run the application and enable assertions for that package, but exclude the class Test?

Answer 12

java -ea:com.demos… -da:com.demos.Test MyMainClass

Question 13

What is the difference between:

java.time.LocalDate
java.time.LocalTime
java.time.LocalDateTime
java.time.ZonedDateTime

Answer 13

• java.time.LocalDate: Date with day, month, year
• java.time.LocalTime: Time of day
• java.time.LocalDateTime: Date and time with no time zone
• java.time.ZonedDateTime: Date and time with a specific time zone

Question 14

What static method exists to get the current value for:

java.time.LocalDate
java.time.LocalTime
java.time.LocalDateTime
java.time.ZonedDateTime

Answer 14

now()

Question 15

What static method can we use to get a specific date?

Answer 15

of()

example:
LocalDate d1 = LocalDate.of(2020, 10, 20);
LocalTime t1 = LocalTime.of(6, 15, 30);
…

Question 16

Create a LocalTime object of 6 hours and 15 minutes.

Answer 16

LocalTime time = LocalTime.of(6, 15);

Question 17

Create a LocalTime object of 6 hours, 15 minutes, 0 seconds and 200 nanoseconds

Answer 17

LocalTime time = LocalTime.of(6, 15, 0, 200);

Question 18

Given the following objects, create a LocalDateTime object.

LocalDate d1 = LocalDate.of(2020, 10, 20);
LocalTime t1 = LocalTime.of(6, 15);

Answer 18

LocalDateTime dt1 = LocalDateTime.of(d1, t1);

Question 19

What class can we use to format a date/time object to display standard formats?

Answer 19

DateTimeFormatter

example:
DateTimeFormatter.ISO_LOCAL_DATE // 2020-10-20
DateTimeFormatter.ISO_LOCAL_TIME // 11:22:34
DateTimeFormatter.ISO_LOCAL_DATE_TIME // 2011-12-03T10:15:30

Question 20

How can we print a date/time object in a custom format?

example: October 20, 2020 at 11:12

Answer 20

using DateTimeFormatter.ofPattern() and use it with the format() method.

example:

var f = DateTimeFormatter.ofPattern(“MMMM dd, yyyy ‘at’ hh:mm”);
somedateobject.format(f);

Question 21

What does the date/time symbol ‘M’ print?

Answer 21

‘M’ = month and prints the index of the month, starting with 1.

Question 22

What does the date/time symbol ‘MM’ print?

Answer 22

‘M’ = month and prints the index of the month, starting with 01.

Question 23

What does the date/time symbol ‘MMM’ print?

Answer 23

‘MMM’ = month and prints the first three letters of the month (example: JUL).

Question 24

What does the date/time symbol ‘MMMM’ print?

Answer 24

‘MMMM’ = month and prints the full month name.

Question 25

What does the date/time symbol ‘a’ print?

Answer 25

‘a’ = a.m./p.m. and prints either AM or PM

Question 26

What does the date/time symbol ‘z’ print?

Answer 26

‘z’ = Time Zone Name and prints the full time zone name.

example: Eastern Standard Time, EST

Question 27

What does the date/time symbol ‘Z’ print?

Answer 27

‘Z’ = Time Zone Name and prints the relative timezone.

example: -0400

Question 28

Given a LocalDateTime dt, why does the following code throw a runtime exception?

var f = DateTimeFormatter.ofPattern(“h:mm z”);
dt.format(f);

Answer 28

LocalDateTime does not have any information of time zones (z).

Question 29

Given a LocalDate dt, why does the following code throw a runtime exception?

var f = DateTimeFormatter.ofPattern(“h:mm”);
dt.format(f);

Answer 29

LocalDate does not have any information of time (h:mm)

Question 30

What other statement does the exact same as the last statement of this code?

var dt = LocalDateTime.of(2020, Month.OCTOBER, 20, 6, 15, 30);
var f = DateTimeFormatter.ofPattern(“MM/dd/yyyy hh:mm:ss”);
dt.format(f)

Answer 30

f.format(dt);

Question 31

Given the following LocalDate, create a formatter to print out: Party’s at October 20, 2020.

LocalDate d1 = LocalDate.of(2020, 10, 20);

Answer 31

DateTimeFormatter formatter = DateTimeFormatter.ofPattern(“‘Party’’s at’ MMMM d, yyyy”);

Question 32

How do we get the current locale?

Answer 32

Locale locale = Locale.getDefault();

Question 33

What does Locale.getDefault() return?

Answer 33

A Locale object containing the locale language (required) and the locale country (optional).

Question 34

Which Locale formats is correct/incorrect?

• US
• en_US
• US_en
• EN
• enUS

Answer 34

All but en_US is incorrect.

Question 35

What are three ways to get a Locale other than the default one?

Answer 35

// 1
Locale.GERMAN // -> de
Locale.GERMANY // -> de_DE

//2
new Locale(“fr”) // fr
new Locale(“hi”, “IN”) //hi_IN
//3
new Locale.Builder()
.setLanguage(“en”)
.setRegion(“US”)
.build()

Question 36

How can you change the default Locale of your Java program? (for testing etc)

Answer 36

Locale.setDefault(someLocaleObjectHere);

Question 37

How do we format the following code to german currency?

double price = 11;

Answer 37

NumberFormat myLocale = NumberFormat.getCurrencyInstance(Locale.GERMANY);

myLocale.format(price);

Question 38

What package does NumberFormat belong to?

Answer 38

java.text

Question 39

How can we format a number to the default locale?

Answer 39

NumberFormat.getInstance()
or
NumberFormat.getNumberInstance()

Question 40

How can we format decimal values to the default locale before displaying?

Answer 40

NumberFormat.getIntegerInstance();

Question 41

How can we format data to a structured object / primitive value, taking into account the Locale?

Answer 41

using NumberFormat.parse();

Question 42

What does the following code return?

var cf = NumberFormat.getCurrencyInstance();
cf.parse(value); //returns what?

Answer 42

A Number object.

Question 43

What are two Locale.Category values?

Answer 43

• DISPLAY
• FORMAT

Question 44

What is a ResourceBundle?

Answer 44

A ResourceBundle contains the locale specific objects to be used by a program. It is like a map with keys and values.

Question 45

Given the ResourceBundle file Zoo_fr

How do you get this Resource Bundle from java code?

Answer 45

ResourceBundle.getBundle(“Zoo”);
or
ResourceBundle.getBundle(“Zoo”, locale);

Question 46

Given a ResourceBundle ‘Zoo’ with the default locale, what happens when requesting a ResourceBundle ‘Zoo’ of a locale that does not exist?

Answer 46

It will return the ResourceBundle with the default locale.

Question 47

What happens when requesting a ResourceBundle of which none exists?

Answer 47

Java will throw a MissingResourceException

Question 48

What is the maximum number of files Java would need to consider to find the appropriate resource bundle with the following code?

Locale.setDefault(new Locale(“hi”));
ResourceBundle rb = ResourceBundle.getBundle(“Zoo”, new Locale(“en”));

Answer 48

three

1. Zoo_en.properties
2. Zoo_hi.properties
3. Zoo.properties

Question 49

What happens when Java cannot find a key in the requested (and existing) resource bundle?

Use the example: Zoo_fr_FR.properties

Answer 49

After checking Zoo_fr_FR.properties, it will go to Zoo_fr.properties. If it doesn’t exist there, it will go to Zoo.properties.

If it also does not exist there it will throw a MissingResourceException.

Question 50

Why should you use the getProperty()/setProperty() over get()/set() methods when working with the Properties class?

Answer 50

With getProperty() you can supply a default value.
With setProperty() you can assure the data can be read

Question 51

Which of the following classes contain at least one compiler error? (Choose all that apply.)

class Danger extends RuntimeException {
public Danger(String message) {
super();
}
public Danger(int value) {
super((String) null);
}
class Catastrophe extends Exception {
public Catastrophe (Throwable c) throws RuntimeException {
super(new Exception());
c.printStackTrace();
}
}
class Emergency extends Danger (
public Emergency () {}
public Emergency (String message) {
super (message);
}
}
A. Danger
B. Catastrophe
C. Emergency
D. All of these classes compile correctly. E. The answer cannot be determined from the information given.

Answer 51

C. Exception and RuntimeException, along with many other exceptions in the Java API, define a no-argument constructor, a constructor that takes a String, and a constructor that takes a Throwable. For this reason, Danger compiles without issue. Catastrophe also compiles without issue. Just creating a new checked exception, without throwing it, does not require it to be handled or declared. Finally, Emergency does not compile. The no-argument constructor in Emergency must explicitly call a parent constructor, since Danger does not define a no-argument constructor,

Question 52

What is the output of the following code?

LocalDate date = LocalDate.parse(“2020-04-30”, DateTimeFormatter. ISO_LOCAL_DATE_TIME);

System.out.println(date.getYear () + “ “
+ date.getMonth() + “ “ + date.getDayOfMonth());

A. 2020 APRIL 2
B. 2020 APRIL 30
C. 2020 MAY 2
D. The code does not compile.
E. A runtime exception is thrown.

Answer 52

E.

A LocalDate does not have a time element. Therefore, a Date/Time formatter is not appropriate. The code compiles but throws an exception at runtime. If ISO_LOCAL_DATE was used, then the code would compile and option B would be the correct answer.

Question 53

What is the output of the following code?

LocalDate date = LocalDate.parse(“2020-04-30”, DateTimeFormatter. ISO_LOCAL_DATE);

System.out.println (date.getYear () + “ “
+ date.getMonth()+””+ date.getDayOfMonth());

A. 2020 APRIL 2
B. 2020 APRIL 30
C. 2020 MAY 2
D. The code does not compile.
E. A runtime exception is thrown.

Answer 53

B.

The code compiles and option B is the correct answer.

Question 54

Assume that all of the files mentioned in the answer choices exist and define the same keys. Which one will be used to find the key in line 8?

6: Locale.setDefault(new Locale(“en”, “US”));
7: var b = ResourceBundle.getBundle (“Dolphins”);
8: System.out.println(b.getString(“name”));

A. Dolphins.properties
B. Dolphins_US.properties
C. Dolphins_en.properties
D. Whales.properties
E. Whales_en_US.properties
F. The code does not compile.

Answer 54

C.

Java will first look for the most specific matches it can find, starting with Dolphins_en_US. properties. Since that is not an answer choice, it drops the country and looks for Dolphins_en.properties, making option C correct. Option B is incorrect because a country without a language is not a valid locale.

Question 55

What is the output of the following code?

LocalDateTime ldt = LocalDateTime.of (2020, 5, 10, 11, 22, 33);
var f = DateTimeFormatter.ofLocalizedTime(FormatStyle. SHORT); System.out.println(ldt.format(f));
A. 3/7/19 11:22 AM
B. 5/10/20 11:22 AM
C. 3/7/19
D. 5/10/20
E. 11:22 AM
F. The code does not compile.
G. A runtime exception is thrown.

Answer 55

E.

Even though ldt has both a date and time, the formatter outputs only time.

Question 56

Identify the correct statement about i18n.

A. I18N class allows you to port your code for multiple regions and/or languages.

B. You should use Locale and formatter objects such as NumberFormat and DateFormat to generate locale specific output.

C. The i18n method of NumberFormat and DateFormat allows you to generate locale specific output.

D. Using default locale for NumberFormat and DateFormat automatically ensures that the formatted text will be localized to the location setting of the machine on which the code is run. (Assuming that default locale hasn’t been explicitly changed by any means.)

E. i18n stands for Internationalization and it is handled automatically by Java.

Answer 56

B, D

A: There is no class named I18N.
E: While i18n indeed stands for Internationalization, it is not done automatically. You have to write code to internationalize your output.