CHP3 - Making Decisions

Question 1

Hierarchy of Number Class

Answer 1

java.lang.Object
↳ java.lang.Number
↳ java.lang.Integer
↳ java.lang.Double
↳ java.lang.Float
↳ java.lang.Long
↳ java.lang.Short
↳ java.lang.Byte
↳ java.util.concurrent.atomic.AtomicInteger
↳ java.util.concurrent.atomic.AtomicLong

Question 2

Pattern Matching

Answer 2

Technique of controlling program flow that only executes a section of code that meets certain criteria.

Question 3

Supported Types of Pattern Matching

Answer 3

The type of the pattern variable must be a compatible type, which includes the same type, a subtype, or a supertype of the reference variable.

Question 4

Shadowing

Answer 4

Shadowing occurs when a variable declared within an inner scope has the same name as a variable in an outer scope. The inner variable “shadows” or hides the outer variable within that block.

int value = 50;
{
int value = 100; // This ‘value’ shadows the outer ‘value’
System.out.println(value); // prints 100
}
System.out.println(value); // prints 50

Question 5

switch variable types

Answer 5

int and Integer
byte and Byte
short and Short
char and Character
String
enum values
All object types (pattern matching)
var (if the type resolves to one of the preceding types)

Question 6

switch (month) {}

Is this valid?

Answer 6

A switch statement is not required to contain any case clauses. This is perfectly valid.

Question 7

Ways to write exhaustive switch

Answer 7

1. Add a default clause.
2. If the switch takes an enum, add a case clause for every possible enum value.
3. Cover all possible types of the switch variable with pattern matching

Question 8

What is yield?

Answer 8

yield keyword is return statement for switch

Question 9

switch and pattern matching

Answer 9

One of the simplest rules when working with switch and pattern matching is that the type cannot be unrelated.
It must be the same type as the switch variable or a subtype.

Question 10

What does it mean switch statement must be exhaustive?

Answer 10

✔ Exhaustiveness means handling all possible values in a switch.
✔ For enums and sealed types, if all cases are covered, default is not needed.
✔ For open types (like Object or Number), a default case is required.

Question 11

continue in switch?

Answer 11

It cannot be used inside of switch

Question 12

private DayOfWeek getWeekDay(int day, final int thursday);

In this method signature, is thursday compile time constant?

Answer 12

No, it is not since any int value can be passed as parameter.

Question 13

case 2. 10: break;

Is it legal in Java?

Answer 13

✔ Valid switch syntax: case 2, 10: is legal in Java 21+ (but not in Java 20 or earlier).

Question 14

Is it valid in case?
case !(Number n) -˃ 3 + n.intValue();

Answer 14

The code does not compile because case clause uses the logical complement operator (!), which is not permitted with pattern matching.

Question 15

do {
5: meters–;
6: if (meters==8) keepGoing = false;
7: result -= 2;
8: } while keepGoing;

Is it valid?

Answer 15

No it is not valid.
Because while condition must be inside of braces.

Question 16

yield attention

Answer 16

Be carefull with:
-semicolon after yield closing brace
-without yield

Question 17

default vs null in switch

Answer 17

default dominates the null

Question 18

Method vs field access

Answer 18

Method calls are resolved at runtime, while field access is resolved at compile time.