Classes, Objects & Methods

Question 1

Class Syntax

Answer 1

class Name {

}

Question 2

When is a main method required in a class?

Answer 2

If the class is the starting point of you program.

Question 3

What types of applications don’t require a main method?

Answer 3

Applets

Question 4

How do you access instance variables from an object?

Answer 4

object.variable

Question 5

How does the Java compiler sort class definitions?

Answer 5

It puts each class into its own .class file.

Question 6

Is it necessary for classes to be in the same source file?

Answer 6

No.

Question 7

Do the contents of the variables in one object differ from another?

Answer 7

Yes, each instance of a class stores its own contents.

Question 8

Object Declaration Syntax

Answer 8

object Name = new object();

Question 9

What does the new operator do?

Answer 9

dynamically allocates memory for an object and returns a reference to it.

Question 10

Reference Variables

Answer 10

Variables referring to objects.

Question 11

Vehicle car1 = new Vehicle();
Vehicle car2 = car1;

Are car1 and car2 referencing the same or different objects?

Answer 11

Same

Question 12

What are methods used for?

Answer 12

Manipulating and providing access to data inside classes.

Question 13

What method begins execution of a program?

Answer 13

The main method

public static void main(String []args)
{
}

Question 14

Method Syntax

Answer 14

type name(param) {

}

Question 15

When is the method Return type void?

Answer 15

If the method doesn’t return a value.

Question 16

How can you cause the immediate termination of a void method prior to its ending brace? What happens to program control?

Answer 16

Return;

Program control returns to the caller.

Question 17

How to return a value in a method?

Answer 17

return value;

Question 18

What methods won’t return values?

Answer 18

Void methods

Question 19

What method will initialize an object, provide initial values to instance variables & perform other startup procedures?

Answer 19

A constructor

Question 20

What do you name a constructor?

Answer 20

The same name as its class

Question 21

What return type should a constructor have?

Answer 21

It has no return type

Question 22

Do all classes have constructors?

Answer 22

Yes, even if not defined, due to a default constructor in the Object class that initializes all member variables to their default values.

Question 23

What are the default values of all member variables?

Answer 23

Zero, null & false

Question 24

Can you add parameters to constructors?

Answer 24

Yes

Question 25

What does garbage collection do?

Answer 25

Reclaims objects automatically

Question 26

When is memory occupied by an object released?

Answer 26

When no references to it exist

Question 27

Under what two conditions will garbage collection run?

Answer 27

There are objects to recycle

There is a need to recycle them

Question 28

What method is used to ensure an object terminates cleanly?

Answer 28

Finalize()

Question 29

When is finalize() called? Who calls it?

Answer 29

Java Runtime calls finalize() just before it recycles the object.

Question 30

What do you include in a finalize() method?

Answer 30

Specify actions that must be performed before the object is destroyed.

Question 31

What implicit argument exists in a method as a reference to the invoking object?

Answer 31

this

Question 32

What distinction does this.variable clarify?

Answer 32

When the name of a parameter or local variable is the same as the name of an instance variable. “this” provides access to the hidden instance variable.

Question 33

Instance variable vs local variable

Answer 33

Local variables are declared in the method or block

Instance variables are declared in the class. They always have a default value.

Question 34

Aliasing

Answer 34

When one object reference is assigned to another. The address is copied, not the object itself, so it’s a different name for the same object.

Question 35

Can an object reference refer to nothing?

Answer 35

Yes, null is a reference to nothing.