Unit 3 part 2 java as OOP

Question 1

Ways of

Argument passing?

Answer 1

1. Pass By value

2. Call by reference

Question 2

Pass By value:

drawbacks too

Answer 2

copy of actual args passed to formal args.
Drawbacks:
In efficient storage allocation, copying arrays,objects is expensive.

When you pass a primitive type to a method, it is passed
by value.

Question 3

Call by reference:

Answer 3

Formal param receive reference to actual data.
aliasing describes a situation in which a data location in memory can be accessed through different symbolic names in the program.
-Note that when we pass a reference, a new reference variable is created. We cannot change the reference to refer to some other object, as the received reference is a copy of the original reference.

Question 4

object as parameter:

Answer 4

One of the most common uses of object parameters
involves constructors. Frequently, you will want to construct
a new object so that it is initially the same as some existing
object.
overloading constructors.

method (classname objvar){}

Question 5

Returning objects:

Answer 5

classname method ( )
{

return obj_of_classname;
}

Question 6

worry of going out of scope?

Objects life span?

Answer 6

Since all objects are dynamically allocated using new, you
don’t need to worry about an object going out-of-scope
because the method in which it was created terminates. The
object will continue to exist as long as there is a reference to
it somewhere in your program. When there are no references
to it, the object will be reclaimed the next time garbage
collection takes place.

Question 7

Features offered by encapsulation:

Answer 7

-encapsulation links data with the code that
manipulates it
-provides access control.
control what parts of a program can access the
members of a class

Question 8

Black Box

Answer 8

Inner workings are not open for tampering

Question 9

Access modifier:

name java’s access modifiers

Answer 9

Determines access, attached to declaration.

public, private, protected.

Question 10

public:

Answer 10

When a
member of a class is modified by public, then that member
can be accessed by any other code.

Question 11

Private:

Answer 11

then that member can only be

accessed by other members of its class.

Question 12

main and its access modifier? why?

Answer 12

main( ) has always been preceded by the
public modifier. It is called by code that is outside the
program—that is, by the Java run-time system.

Question 13

Default access modifier:

Answer 13

When no
access modifier is used, then by default the member of a
class is public within its own package, but cannot be
accessed outside of its package

Question 14

protected:

Answer 14

Comes in picture during inheritance

Question 15

static is used for?

example?

Answer 15

Allows using a class member independently of any object.

• When a member is declared static, it can be accessed before any objects of its class are created, and without reference to any object
• methods and variables can be static

main( ) is declared as static because it must be
called before any objects exist.

Question 16

Static variables?

Answer 16

Instance variables declares as static are essentially global variables.

• when object of class is created, copy of these static variables is not created.
• All instances of class share same static variables.

Question 17

Static methods rules?

Answer 17

• They can only directly call other static methods of
their class.
• They can only directly access static variables of
their class.
• They cannot refer to this or super in any way. (The
keyword super relates to inheritance and is described in
the next chapter.)

Question 18

Static block and use of static in class:

Answer 18

As soon as class is loaded, all static statements are run.

static BLOCK:

static{ initialise stuff; code; }

If you need to do computation in order to initialize your
static variables, you can declare a static block that gets
executed exactly once, when the class is first loaded.

Question 19

Access static method, var outside class:

Answer 19

classname.method( )

specify the name of their
class followed by the dot operator

Question 20

final :

what does it do?

who can be declared as it?

Answer 20

A field can be declared as final. Doing so prevents its
contents from being modified, making it, essentially, a
constant. This means that you must initialize a final field
when it is declared. You can do this in one of two ways: First,
you can give it a value when it is declared. Second, you can
assign it a value within a constructor.
uppercase identifiers for final fields

method params, local vars can also be declared as firelds.

Declaring a parameter final
prevents it from being changed within the method. Declaring
a local variable final prevents it from being assigned a value
more than once.

final for methods is different.

Question 21

Nested class:

Scope and lifespan and

Answer 21

It is possible to define a class within another class; such
classes are known as nested classes.

The scope of a nested
class is bounded by the scope of its enclosing class.

A nested class has access to the
members, including private members, of the class in which it
is nested. However, the enclosing class does not have access
to the members of the nested class.

Question 22

It is also possible to declare a
nested class that is local to a block.

Answer 22

I dont understand

Question 23

explain types of nested class:

Answer 23

Static and non static:

Static must access the nonstatic members of its enclosing class through an object. That
is, it cannot refer to non-static members of its enclosing
class directly.

Question 24

Inner class:

Answer 24

An inner class is a non-static nested class. It has access to all
of the variables and methods of its outer class and may refer
to them directly in the same way that other non-static
members of the outer class do.

Question 25

Creating Instance of outer class:

Answer 25

It is important to realize that an instance of Inner can be
created only in the context of class Outer. The Java compiler
generates an error message otherwise. In general, an inner
class instance is often created by code within its enclosing
scope, as the example does.