Chapter 16: 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

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

Answer 9

Nothing happens and Java will continue execution.

Question 10

How can we enable assertions using the java command?

Answer 10

// single-file source-code

• java -ea SomeFile.java
• java -enableassertions SomeFile.java

// normal

• java -ea SomeFile
• java -enableassertions SomeFile

Question 11

By default, assertions are enabled or disabled?

Answer 11

disabled.

Question 12

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

Answer 12

java -ea:com.demos… MyMainClass

Question 13

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

Answer 13

java -ea:com.demos.Test MyMainClass

Question 14

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

Answer 14

-da or -disableassertions

Question 15

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 15

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

Question 16

Why should assertions never alter outcomes?

example:
int x = 10;
assert ++x > 10;

Answer 16

This is not a good use of assertions because the outcome of the code will be different depending on wether assertions are turned on.

Question 17

What is the difference between:

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

Answer 17

• 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 18

What static method exists to get the current value for:

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

Answer 18

now()

Question 19

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

Answer 19

of()

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

Question 20

Create a LocalTime object of 6 hours and 15 minutes.

Answer 20

LocalTime time = LocalTime(6, 15);

Question 21

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

Answer 21

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

Question 22

Given the following objects, create a LocalDateTime object.

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

Answer 22

LocalDateTime dt1 = new LocalDateTime(d1, t1);

Question 23

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

Answer 23

DateTimeFormatter

example:
DateTimeFormatter.ISO_LOCAL_DATE // 2020-10-20
DateTimeFormatter.ISO_LOCAL_TIME // 11:22:34
DateTimeFormatter.ISO_LOCAL_DATE_TIME

Question 24

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

example: October 20, 2020 at 11:12

Answer 24

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 25

What does the date/time symbol 'M' print?

Answer 25

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

Question 26

What does the date/time symbol 'MM' print?

Answer 26

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

Question 27

What does the date/time symbol 'MMM' print?

Answer 27

'M' = month and prints the first three letters of the month (example: JUL).

Question 28

What does the date/time symbol 'MMMM' print?

Answer 28

'M' = month and prints the full month name.

Question 29

What does the date/time symbol 'a' print?

Answer 29

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

Question 30

What does the date/time symbol 'z' print?

Answer 30

'z' = Time Zone Name and prints the full time zone name. example: Eastern Standard Time, EST

Question 31

What does the date/time symbol 'Z' print?

Answer 31

'z' = Time Zone Name and prints the relative timezone. example: -0400

Question 32

Given a LocalDateTime dt, why does the following code throw a runtime exception? ``` var f = DateTimeFormatter.ofPattern("h:mm z"); dt.format(f); ```

Answer 32

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

Question 33

Given a LocalDate dt, why does the following code throw a runtime exception? ``` var f = DateTimeFormatter.ofPattern("h:mm"); dt.format(f); ```

Answer 33

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

Question 34

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 34

f.format(dt);

Question 35

Given the following LocalDate, create a formatter to print out: Party's at October 20, 2020. LocalDate d1 = LocalDate.of(2020, 10, 20);

Answer 35

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("'Party''s at' MMMM d, yyyy");

Question 36

Given a LocalDate dt, why does the following code throw a runtime exception? DateTimeFormatter.ofPattern("'Time is: hh:mm: ");

Answer 36

There is an incomplete escape sequence (').

Question 37

What is Internationalization?

Answer 37

It is the process of designing your program so it can be adapted. This involves placing strings in a properties file and ensuring the proper data formatters are used.

Question 38

What is Localization?

Answer 38

supporting multiple locales or geographic regions and includes translating string to different languages and outputting dates and numbers in the correct format for that locale.

Question 39

How do we get the current locale?

Answer 39

Locale locale = Locale.getDefault();

Question 40

What does Locale.getDefault() return?

Answer 40

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

Question 41

Which Locale formats is correct/incorrect? - US - en_US - US_en - EN - enUS

Answer 41

All but en_US is incorrect.

Question 42

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

Answer 42

// 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 43

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

Answer 43

Locale.setDefault(someLocaleObjectHere);

Question 44

How do we format the following code to german currency? double price = 11;

Answer 44

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

Question 45

What package does NumberFormat belong to?

Answer 45

java.text

Question 46

How can we format a number to the default locale?

Answer 46

NumberFormat.getInstance() or NumberFormat.getNumberInstance()

Question 47

How can we format a percentage to the default locale?

Answer 47

NumberFormat.getPercentInstance()

Question 48

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

Answer 48

NumberFormat.getIntegerInstance();

Question 49

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

Answer 49

using NumberFormat.parse();

Question 50

What does the following code return? ``` var cf = NumberFormat.getCurrencyInstance(); cf.parse(value); //returns what? ```

Answer 50

A Number object.

Question 51

What are two Locale.Category values?

Answer 51

- DISPLAY | - FORMAT

Question 52

What is the Locale.Category value DISPLAY?

Answer 52

Category used for displaying data about the locale.

Question 53

What is the Locale.Category value FORMAT?

Answer 53

Category used for formatting dates, numbers, or currencies.

Question 54

What is a ResourceBundle?

Answer 54

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

Question 55

Given the ResourceBundle file Zoo_fr | How do you get this Resource Bundle from java code?

Answer 55

ResourceBundle.getBundle("Zoo"); or ResourceBundle.getBundle("Zoo", locale);

Question 56

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

Answer 56

It will return the ResourceBundle with the default locale.

Question 57

What happens when requesting a ResourceBundle of which none exists?

Answer 57

Java will throw a MissingResourceException

Question 58

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 58

three 1. Zoo_en.properties 2. Zoo_hi.properties 3 Zoo.properties (page 783)

Question 59

What happens when Java cannot find a key in the requested (and existing) resource bundle? Use the example: Zoo_fr_FR.properties

Answer 59

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 60

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

Answer 60

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