Working with local classes

Question 1

What are global classes in ABAP and how are they stored?

Answer 1

Global classes in ABAP are stored centrally in a class pool and contain reusable logic for other ABAP programs.

Question 2

What are local classes in ABAP and where are they defined?

Answer 2

defined within a program or a global class, restricted to use within their defining scope.

Question 3

How can you quickly create a new local class

Answer 3

typing “lcl” and then pressing strg+leertaste, adjust name of the class

Question 4

What are the two parts of code of a class called

Answer 4

Definition and implementation. The definition part of a class is subdivided into up to three sections, called the visibility sections of the class (public, protected, private section).

Question 5

What does the TYPES statement allow within a class in ABAP?

Answer 5

defining types within a class, similarly to outside a class. If types are public, programs using the class can use these types for their variables.

Question 6

How do you declare attributes in an ABAP class?

Answer 6

Attributes in an ABAP class are declared using DATA for instance attributes and CLASS-DATA for static attributes.

Question 7

How are constants declared within ABAP classes?

Answer 7

Constants within ABAP classes are declared using CONSTANTS. They, along with types, are static components of the class.

Question 8

How are methods defined within ABAP classes?

Answer 8

METHODS for instance methods and CLASS-METHODS for static methods. The method’s name is followed by its signature, including the values exchanged with its caller and possible exceptions..

Question 9

How do you access the local classes within your globall class

Answer 9

on the bottom below the code editor are different tabs. One of them is called local types. Create a new local class by typing lcl and then strg+leer there. Remember to give it a name (“lcl_…”)

Question 10

Inside the class you work with attributes like with normal variables. How do you access static attributes outside though?

Answer 10

<class_name>=><static_attribute>
lcl_connection=>conn_counter = 5.
no blank spaces!

"=>" is called the static component selector
</static_attribute></class_name>

Question 11

What is a reference variable

Answer 11

a special variable that is used to create, address and manage an object. It points at the instance of a class in the program memory

Question 12

How do you declare a reference variable

Answer 12

DATA <referenceVariable> TYPE REF TO <className></className></referenceVariable>

Question 13

How do you create a new instance of a class

Answer 13

With the NEW operator.
connection = NEW #( )
the hashtag means use the type of the variable before the equals sign, which is declared through the DATA … TYPE REF TO … part.
It is also possible to replace the hashtag with the name of the class

Question 14

What is the difference between a normal and a static attribute

Answer 14

A normal attribute is unique for each single object. A static one is shared between each object. So if one object changes a static attribute, that value is simultaneously changed for all other objects of that type

Question 15

Static components are adressed with the classname and “=>”. How are instance components attributes adressed?

Answer 15

With the instance component selector “->”:

<reference_variable>-><attribute>

connection->carrier_id = 'LH'.
</attribute></reference_variable>

Question 16

What is the consequence if you code sth. like this
con = NEW #( ).
con2 = NEW #( ).

Answer 16

they both point to the same memory address. So if you change one of them, you “change the other one” as well

Question 17

What happens when you write:
con = NEW #( ).
con = NEW #( ).

Answer 17

The reference variable will no longer point to the first object, but rather to the second oe. Therefore, nothing points to the object generated during the first call. It will therefore be deleted by the garbage collector.

Question 18

How could you prevent the deletion of an object even though you use con = NEW #( ).
several times?

Answer 18

By saving it in an internal table

Question 19

How do you create new methods?

Answer 19

Within the public/private/protected section of a class:
METHODS method_name
IMPORTING
i_helper TYPE i.
EXPORTING
e_helper TYPE i.

Importing is what variables are being fed to the method and export vice verca. These methods need an implementation in the IMPLEMENTATION section

Question 20

When a piece of code is underlined in red squiggly lines, how do you access the quick fix menu for it

Answer 20

Strg + 1, or right click -> quick fix

Question 21

What kind of attributes are instance and static methods allowed to access

Answer 21

instance methods can access instance and static attributes.
Static methods can only access static attributes.

Question 22

Within the implementation of instance methods, ABAP offers the built in variable “ME”. Describe its purpose

Answer 22

ME is a reference variable, typed with the current class and filled at runtime with the address of the current instance. The use of ME is optional and should be avoided, unless the name of an attribute collides with the name of another data object, for example a parameter name.

Example:
Definition part of the class:
DATA carrier_id TYPE i.
…
METHODS set_attributes
IMPORTING
carrier_id TYPE i

now we have the case, where the parameter carrier_id in METHODS has the same name as the attribute carrier_id. The name itself would trherefore denote the parameter. To access the attribute of the current instance, we need “me->”:

Implementation part of the class:
METHOD set_attributes.
me->carrier_id = carrier_id.

Question 23

How can a method raise an exception

Answer 23

Within the method body, you can type:
RAISE EXCEPTION TYPE <exception_class>.
Execution will be terminated and control returned to method caller, if possible (raising clause, try endtry and catch block need to exist. quickfix can help with that)</exception_class>

Question 24

How are instance and static methods called

Answer 24

Instance methods:

<reference_variable>-><method_name>(
EXPORTING
IMPORTING
CHANGING
).

Static methods:
<class_name>=><static_method>(
...
).
</static_method></class_name></method_name></reference_variable>

Question 25

What difference does the keyword VALUE make here:

METHODS get_output
RETURNING
VALUE(r_output) TYPE STRING_TABLE.

Answer 25

By adding VALUE, the value itself will be passed and can be used in a variable. If we would not use VALUE, we would only pass the parameter by reference, basically just the pointer to the memory location. This means any changes made to the parameter within the method will affect the original data outside the method.

Question 26

What are the components of a method’s signature?

Answer 26

The components of a method’s signature include parameters and exceptions. Each parameter in the signature consists of a name and a type.

Question 27

What are the different types of parameters in a method, and how are they defined?

Answer 27

Importing Parameters: These are values received by the method from the caller. They can be made optional using the OPTIONAL addition or assigned a default value using the DEFAULT <val> addition.</val>

Exporting Parameters: Results returned by the method, optional for the caller.

Changing Parameters: Received values that can be altered and returned.

Returning Parameters: This is a method result that can be directly used in an expression. Only one returning parameter is allowed per method, and it uses pass-by-value parameter passing, denoted by surrounding the parameter name in brackets and preceding it with the keyword VALUE.

Exceptions (RAISING): Indicates potential errors for the calling program to handle.

Question 28

How are importing, exporting, and changing parameters defined when CALLING a method?

Answer 28

Importing Parameters: Listed after the keyword EXPORTING, these values are provided by the calling program and are essential for the method. The parameter names are on the left side of an equals sign (=), with an expression on the right side, matching the parameter’s type.

Exporting Parameters: Listed after the keyword IMPORTING, these results are returned by the method to the calling program. The parameter name is on the left side of an equals sign (=), and the right side variable must match the parameter’s type.

Changing Parameters: Listed after the keyword CHANGING, these values are passed by the calling program and can be modified by the method. The type of the variable on the right side must match the parameter’s type.

Example for Method with importing parameters:
connection->set_attributes(
EXPORTING
i_carrier_id = ‘LH’).

Question 29

How can you generate a method call, including parameter passing, using code completion in ADT?

Answer 29

Type in the reference variable or class name followed by the component selector (->/=>).

Press Ctrl + Space to display a list of components available.

Select a method from the list and press Shift + Enter to insert the method’s name and full signature into your code, including optional parameters listed in comment lines.

Question 30

What is the process for generating a method call, including parameter passing, using code completion in ADT?

Answer 30

Type in the reference variable or class name followed by the component selector (->).

Press Ctrl + Space to display a list of available attributes and methods.

Choose the desired method from the list.

Press Shift + Enter to insert the full signature of the method, including parameters.

Question 31

What does an object represent in object-oriented programming?

Answer 31

An object represents a real-life entity and contains attributes defining its characteristics, such as carrier ID and flight number for a flight connection.

Question 32

What is data encapsulation in object-oriented programming?

Answer 32

Data encapsulation restricts direct access to an object’s internal state, requiring operations to be performed through predefined methods, enhancing data integrity and control.

Question 33

Why is data encapsulation advantageous in object-oriented programming?

Answer 33

Data encapsulation enhances data integrity, reduces the risk of unintended changes, and promotes modular design, leading to more robust and maintainable code.

Question 34

How can attribute access be restricted in object-oriented programming?

Answer 34

Attribute access can be restricted by adding READ-ONLY to public section attributes or by moving them to a different section like private.

By making your attributes private - or read-only, at least - you can ensure that the client program uses the available set_attributes( ) method to set the values for attributes carrier_id and connection_id.

Question 35

How can you quickly change attribute visibility in ADT?

Answer 35

Place the cursor on the attribute, press Ctrl + 1, and select “Make <attribute> private" from the options.</attribute>

Question 36

How can inconsistencies in attribute initialization and modification be addressed in object-oriented programming?

Answer 36

By using constructor methods, which are automatically called by the runtime system when creating a new instance of a class. Constructors enforce non-initial values during instantiation and prevent later changes to attributes.

Question 37

What are the properties of a constructor method in object-oriented programming?

Answer 37

A constructor method is a public instance method with the reserved name “constructor.” It may have importing parameters to obtain starting values for attributes and may raise exceptions.

Question 38

How can you generate a constructor method in ABAP Development Tools (ADT)?

Answer 38

Place the cursor on the class name, press Ctrl + 1, and choose “Generate constructor” from the quick fixes. Then select the attributes to initialize with the constructor and adjust its definition and implementation as needed.

Question 39

What is a static constructor, also known as a class constructor, in ABAP?

Answer 39

A static constructor is a public static method with the reserved name class_constructor. It is called once when the class is first addressed during program execution and is typically used for dynamic initialization of static attributes.

Question 40

When is a static constructor called in ABAP?

Answer 40

The static constructor is called once when the class is first addressed during program execution, which could be during the first instantiation of the class, the first call of a static method, or the first access to a public static attribute.

Question 41

What are the properties of a static constructor method in ABAP?

Answer 41

A static constructor method has the reserved name class_constructor, is public and static, and does not have any parameters or exceptions. It is automatically invoked by the runtime system when the class is first addressed during program execution.

Question 42

In which order do you define the visibility sections of a class?

Answer 42

public section, protected section, private section

Question 43

A functional method must have:
A Exactly one returning parameter

B No changing parameters

C Exactly one exporting parameter

D Exactly one importing parameter

Answer 43

A: exactly one returning parameter

Question 44

The static constructor is executed when the class is addressed for the first time. When might this be?

A When you call a static method of the class.

B At the beginning of the program.

C When you instantiate the class.

Answer 44

A When you call a static method of the class.

C When you instantiate the class.

Question 45

You have declared two reference variables, ref1 and ref2. ref1 points to an object. You now execute the statement
ref2 = ref1. What happens?

A

The ABAP system assigns the address of the object to which ref1is pointing to reference variable ref2. There is only one
object.

B

The ABAP system creates a copy of the object to which ref1 is pointing and assigns its address to ref2. There are now
two objects.

Answer 45

A

The ABAP system assigns the address of the object to which ref1is pointing to reference variable ref2. There is only one
object.

Question 46

Q5. A class my_class contains the public static method my_method. What is the correct code to call this method?

A

my_class=>my_method().

B

my_class=>my_method().

C

my_class->my_method().

D

my_class->my_method().

Answer 46

B

my_class=>my_method().

Question 47

Q6. You have defined a class containing instance attributes and static attributes. You have also declared a reference
variable but not yet created an instance of the class. Which components of the class can you access at this point,
and how?

A

Instance components using the reference variable.

B

Static components using the reference variable.

C

Static components using the name of the class.

D

Instance components using the name of the class.

Answer 47

C

Static components using the name of the class.

Question 48

Q7. Which of the following signature elements may an instance constructor have?

A

Exporting parameters

B

Changing parameters

C

Importing parameters

D

Exceptions

Answer 48

C

Importing parameters

D

Exceptions

Question 49

Q8. Your class contains a public instance attribute attr. How could you ensure that its value can only be changed within
the class?

A

Convert it into a constant.

B

Make it a private attribute.

c

Move it to a different local class.

D

Leave it in the public section but use the READ-ONLY addition.

Answer 49

B

Make it a private attribute.

D

Leave it in the public section but use the READ-ONLY addition.