Chapter 3

Question 1

System.out.println(1 + 2 + “c”); ?

Answer 1

3c

Question 2

String s1 = “1”;
String s2 = s1.concat(“2”);
s2.concat(“3”);
System.out.println(s2);

?

Answer 2

12

Question 3

String pool or intern pool is what?

Answer 3

A location in the JVM that collects reusable strings.

Question 4

Which is less efficient. Why?
String name = "Fluffy";
String name = new String("Fluffy");

Answer 4

new keyword is less efficient as string pool is not used. Here fluffy is not a literal.

Question 5

How do these string methods work?
length()
charAt()
indexOf()
substring()

Answer 5

string. length();
string. charAt(5);
string. indexOf(char, index);
string. substring(begin, end);
string. substring(begin);

Question 6

write these string methods:
startsWith()
endsWith
equals

Answer 6

“abc”.startsWith(“a”) // true
“Abc”.endsWith(“c”) // true
“Abc”.equals(“abc”) // false

Question 7

String methods:
replace()
contains()

Answer 7

“abcabc”.replace(‘a’, ‘A’);
“abcabc”.replace(“a”, “A”);
“Abc”.contains(“b”);

Question 8

Stringbuilder, immutable or mutable? And String?

Answer 8

Mutable, i.e. Changeable.

String however is immutable, unchangeable.

Question 9

Logical equality vs object equality for strings?

Answer 9

== is object/reference equality
.equals is logical equality
Strings have special equals method, usually .equals checks reference equality.

Question 10

Which is which? parseBoolean(“true”) valueOf(“TRUE”)

Answer 10

First converts string to primitive. Second string to wrapper class.

Question 11

Which wrapper class constructors need casts?

Answer 11

new Byte((byte) 1)
new Short((short) 1)

Question 12

What is a fixed size list or backed list?

Answer 12

An array changed into a basic List (not an ArrayList). Using set() on this List updates both array and list.
List list = Arrays.asList(array)

Question 13

Sort an array?

Sort an ArrayList?

Answer 13

Arrays.sort(array);

Collections.sort(arraylist);

Question 14

What are the three time classes? Do they have constructors?

Answer 14

LocalTime, LocalDate, LocalDateTime.
No, example:
LocalTime time = LocalTime.of(6,15);

Question 15

Is LocalDate mutable or immutable?

Answer 15

Immutable. Therefore must assign to reference when manipulating it.