Week 4 Part 2

Question 1

T/F - We declare the main method static so that the JVM can invoke ClassName.Main() without creating an instance of the class

Answer 1

True

Question 2

T/F - Static variables can only be used in some of the classes methods

Answer 2

False. They can be used in all them as they have “class scope”.

Question 3

ClassName.StaticMethod() - Does this work?

Answer 3

Yes

Question 4

How do private static class members differ from public ones?

Answer 4

They can only be accessed by through the methods of the class

Question 5

Can static methods access a class’ instance variables and instance methods?

Answer 5

No. Because static methods exist before any objects of the class have been instantiated.

Question 6

Can the “this” reference be used in a static method? Why?

Answer 6

No. Because static methods are loaded before anything else. There’s no “this.var” to grab

Question 7

T/F - A static variable is given a default value if it is not initalized

Answer 7

True

Question 8

A static method calls an instance method of the same class by using only the method name, what happens?

Answer 8

Compilation error

Question 9

A static method attempts to access an instance variable in the same class by using only the variable name, what happens?

Answer 9

Compilation error

Question 10

What can a static method directly relate to?

Answer 10

Other static members that have been loaded with the class

Question 11

Can instance methods relate to static methods? how about other instance methods?

Answer 11

They can relate to both.

Question 12

public class JustTheStatic {
public String me = “Mine”;
public static void main(String[] args){
System.out.println(“Now” + me); }

What happens here? Does it run?

Answer 12

It does not run. Despite being a part of a static class “me” is not static. Therefore when main attempts to run “me” is not yet in memory.

Question 13

T/F - Static objects in Java are immutable

Answer 13

False

Question 14

T/F - String objects are immutable

Answer 14

True. (Cannot be modified after they are created)

Question 15

When we concatenate two strings together what happens? (Hint - immutable)

Answer 15

A new string is created containing the concatenated values. Original string values are not modified.

Question 16

Typically, the garbage collector _____ eventually reclaim the memory for any objects that are eligible

Answer 16

MIGHT

Question 17

T/F - The JVM guarantees the garbage collector will execute, at the right time

Answer 17

False

Question 18

T/F - The garbage collector will collect each eligible object when the time comes

Answer 18

False. May collect no objects or simple a subset of eligible ones

Question 19

Principle of least privilege - Is it important? What is it?

Answer 19

It’s fundamental to good software engineering. It suggests that code should only be granted enough privileges to accomplish its designated tasks.

Question 20

How does the principle of least privilege make your code better?

Answer 20

Prevents code from accidentally modifying variable values and calling methods that should not be accessible.

Question 21

final variables can be initialized when they are declared or by each __________, so that each object of the class has a different value

Answer 21

constructor

Question 22

If a class with final vars has multiple constructors, what would each one be required to do?

Answer 22

Initialize each final variable (assuming it’s not done by the class)

Question 23

What happens if a final variable is not initalized?

Answer 23

A compilation error

Question 24

When a class has references to objects of other classes as members

Answer 24

Composition (has-a relationship)
IE. AlarmClock objects need current time and the time when it is to sound its alarm, therefore it would have 2 references to time objects and in AlarmClock