Java APIs

Question 1

The date and

time classes have private constructors to force you to use the static methods.

Answer 1

Don’t fall for this. You are not allowed to construct a date or time object directly

Question 2

LocalDate

Answer 2

Contains just a date—no time and no time zone

2015-01-20

Question 3

LocalTime

Answer 3

Contains just a time—no date and no time zone.

12:45:18.401

Question 4

LocalDateTime

Answer 4

Contains both a date and time but no time zone
2015-01-20T12:45:18.401

Java uses T to
separate the date and time when converting LocalDateTime to a String.

Question 5

You need an import statement to work with the date and time classes.

Answer 5

import java.time.*;

Question 6

Autoboxing

Answer 6

Since Java 5, you can just type the primitive value and Java will convert it to the
relevant wrapper class for you. This is called autoboxing.

Question 7

The parse methods, such as parseInt(), return a primitive

Answer 7

the valueOf() method returns a wrapper class

Question 8

MMMM

Answer 8

M represents the month. The more Ms you have, the more verbose the Java output.
For example, M outputs 1, MM outputs 01, MMM outputs Jan, and MMMM outputs January.

Question 9

dd

Answer 9

d represents the date in the month. As with month, the more ds you have, the more
verbose the Java output. dd means to include the leading zero for a single-digit month.

Question 10

yyyy

Answer 10

y represents the year. yy outputs a two-digit year and yyyy outputs a four-digit year.

Question 11

mm

Answer 11

m represents the minute.

Question 12

ISO is a standard for dates.

Answer 12

DateTimeFormatter.ISO_LOCAL_DATE
2020-01-20

DateTimeFormatter.ISO_LOCAL_TIME
11:12:34

DateTimeFormatter.ISO_LOCAL_DATE_TIME
2020-01-20T11:12:34
(T separates date from time)

Question 13

rules to know

Answer 13

1. If both operands are numeric, + means numeric addition.
2. If either operand is a String, + means concatenation.
3. The expression is evaluated left to right.

Question 14

Immutability

Answer 14

An object that can’t be changed once it’s created. String is immutable.

Mutable is another word for changeable.