Chapter 1: Declarations and Access Control

Question 1

What can identifiers begin with?

Answer 1

Identifiers can begin with a letter, an underscore, or a currency character.

Question 2

Can identifiers include digits?

Answer 2

Yes, after the first character, identifiers can also include digits.

Question 3

Does an identifier have a length limit?

Answer 3

No, identifiers can be of any length.

Question 4

What two commands are used to compile and execute Java programs?

Answer 4

javac and java.

Question 5

What main() signature has special powers?

Answer 5

Method signatures equivalent to public static void main(String[] args)

Question 6

Can the main() be overloaded?

Answer 6

Yes, main() can be overloaded.

Question 7

What is the purpose of an Import statement?

Answer 7

An import statement’s only job is to save keystrokes.

Question 8

What symbol is used to search through the contents of a single package?

Answer 8

asterisk (*) to search through the contents of a single

package.

Question 9

What syntax is correct: “Static Import” or “Import Static”

Answer 9

The syntax is import static….

Question 10

What type of classes can be imported?

Answer 10

You can import API classes and/or custom classes.

Question 11

How many public classes can a source file have?

Answer 11

A source code file can have only one public class.

Question 12

When is a filename required to have the same name as a class?

Answer 12

If the source file contains a public class, the filename must match the
public class name.

Question 13

How many package statements can a file have?

Answer 13

A file can have only one package statement, but it can have multiple
imports.

Question 14

Where should a import statement appear in a file?

Answer 14

The import statements (if any) must come after the package and before the class declaration.

If there is no package statement, import statements must be the first (noncomment) statements in the source file.

Question 15

What classes do package and import statements affect?

Answer 15

package and import statements apply to all classes in the file.

Question 16

True or False: A file can only have one class.

Answer 16

False - A file can have more than one nonpublic class.

Question 17

True or False: Files with no public classes have no naming restrictions.

Answer 17

True - Files with no public classes have no naming restrictions.

Question 18

What are the three access modifiers?

Answer 18

There are three access modifiers: public, protected, and private.

Question 19

What are the four access levels?

Answer 19

There are four access levels: public, protected, default, and private.

Question 20

True or False: Classes can have protected and private access.

Answer 20

False - Classes can have only public or default access.

Question 21

What classes can access a class with default access?

Answer 21

A class with default access can be seen only by classes within the same package.

Question 22

What does class visitability revolve around?

Answer 22

Class visibility revolves around whether code in one class can

• Create an instance of another class
• Extend (or subclass) another class
• Access methods and variables of another class

Question 23

True or False: A class can be both final and abstract.

Answer 23

False - A class cannot be both final and abstract.

Question 24

True or False: A final class cannot be subclassed.

Answer 24

True - A final class cannot be subclassed.

Question 25

True or False: An abstract class can be instantiated.

Answer 25

False - An abstract class cannot be instantiated.

Question 26

True or False: A concrete class can have an abstract method.

Answer 26

False - A single abstract method in a class means the whole class must be
abstract.

Question 27

True or False: An abstract class can have abstract and non abstract methods.

Answer 27

True - An abstract class can have both abstract and nonabstract methods.

Question 28

What must the first class that extends an abstract class do?

Answer 28

The first concrete class to extend an abstract class must implement all of its abstract methods.

Question 29

What are Interfaces?

Answer 29

Interfaces are contracts for what a class can do, but they say nothing about the way in which the class must do it.

Question 30

What type of class can implement an interface?

Answer 30

Interfaces can be implemented by any class, from any inheritance tree.

Question 31

True or False: An interface is like a 100-percent abstract class and is implicitly abstract whether you type the abstract modifier in the declaration or not.

Answer 31

True - Except in Java 8 Statics and Default methods can have implementation.

Question 32

What two modifiers are applied to interface methods by default?

Answer 32

public and abstract—explicit declaration of these modifiers is optional.

Question 33

What three modifiers are applied to interface fields by default?

Answer 33

Interfaces can have constants, which are always implicitly public, static, and final. (optional in any combination.)

Question 34

What are the properties of a legal non-abstract implementing class?

Answer 34

It provides concrete implementations for the interface’s methods.

It must follow all legal override rules for the methods it implements.

It must not declare any new checked exceptions for an implementation method.

It must not declare any checked exceptions that are broader than the exceptions declared in the interface method.

It may declare runtime exceptions on any interface method implementation regardless of the interface declaration.

It must maintain the exact signature (allowing for covariant returns) and return type of the methods it implements (but does not have to declare the exceptions of the interface).

Question 35

True or False: A class implementing an interface cannot be abstract.

Answer 35

False - A class implementing an interface can itself be abstract.

Question 36

True or False: An abstract implementing class must implement the interface methods.

Answer 36

False - An abstract implementing class does not have to implement the interface methods (but the first concrete subclass must).

Question 37

In terms of inheritance, what is the main difference between a class and an interface?

Answer 37

A class can extend only one class (no multiple inheritance), but it can implement many interfaces.

Question 38

True or False: An interface can extend one or more other interfaces.

Answer 38

True - Interfaces can extend multiple interfaces.

Question 39

Can interfaces extend a class or implement a class or interface?

Answer 39

No, interfaces cannot extend a class or implement a class or interface.

Question 40

What is a member of a class?

Answer 40

Methods and instance (nonlocal) variables are known as “members.”

Question 41

What access levels can members have?

Answer 41

Members can use all four access levels: public, protected, default, and private.

Question 42

When can a member be accessed without the ( . ) operator?

Answer 42

Members accessed without the dot operator (.) must belong to the same class.

this.aMethod() is the same as just invoking aMethod().

Question 43

What is the proper way to declare a var-arg?

Answer 43

A var-arg parameter is declared with the syntax type… name; for instance: doStuff(int… x) { }.

Question 44

True or False: A var-arg parameter type can appear anywhere in a parameter list along side normal parameters.

Answer 44

False - In methods with normal parameters and a var-arg, the var-arg must come last.

Question 45

True or False: Instance variables can’t be abstract, synchronized, native, or strictfp.

Answer 45

True: However, they can have any access level and be marked final.

Question 46

What is it called when a local variable has the same name as an instance variable?

Answer 46

This is called “shadowing.”

Question 47

True or False: final variables can refer to different objects once the object has been assigned to a final variable.

Answer 47

False - final reference variables cannot refer to a different object once the object has been assigned to the final variable.

Question 48

When must a final variable be initialized?

Answer 48

Before the constructor completes.

Question 49

True or False: Java allows for final objects.

Answer 49

False - There is no such thing as a final object. An object reference marked final does NOT mean the object itself can’t change.

Question 50

True or False: An array is an object.

Answer 50

True - Arrays can hold primitives or objects, but the array itself is always an object.

Question 51

True or False: Array brackets can only appear to the left of the variable name.

Answer 51

False - When you declare an array, the brackets can be to the left or to the right of the variable name.

Question 52

When is it legal to declare the size of an array in the declaration?

Answer 52

It is never legal to include the size of an array in the declaration.

Question 53

True or False: An array of type animal cannot hold any subclasses of the animal type.

Answer 53

False - An array of objects can hold any object that passes the IS-A (or instanceof) test for the declared type of the array. For example, if Horse extends Animal, then a Horse object can go into an Animal array.

Question 54

If a variable is marked static, it is not tied to _____.

Answer 54

any particular instance of a class.

Question 55

True or False: A class instance is required to use a its static methods.

Answer 55

False - No class instances are needed in order to use static members of the class.

Question 56

How many copies of a static/class variable are available to instances of that class?

Answer 56

There is only one copy of a static variable/class and all instances share it.

Question 57

True or False: static methods do not have direct access to nonstatic members.

Answer 57

True - Static methods are unaware of instances. However, instances are aware of static variables/methods.