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Home Oracle 1z0-804

Oracle 1z0-804 Exam Practice Questions (P. 5)

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Question #21
Given:

Which three statements concerning the OO concepts "is-a" and "has-a" are true?
  1. A
    Flimmer is-a Plinkable
  2. B
    Flommer has-a Tagget
  3. C
    Flommer is-a Glommer
  4. D
    Tagget has-a String
  5. E
    Flommer is-a Plinkable
  6. F
    Flimmer is-a Flommer
  7. G
    Tagget is-a Plinkable

Correct Answer:
ABE
A: Flimmer implements Plinkable.
Flimmer is-a plinkable.
D:The relationship modeled by composition is often referred to as the "has-a" relationship. HereTaggethasaString.

F: Flommer extends Flimmer -
So there is an "is-a relationship between Flommer and Flimmer .
Note: Thehas-a relationship has anencapsulation feature (like private or protected modifier used before each member field or method).

Question #22
Which two compile?
  1. A
    interface Compilable { void compile(); }
  2. B
    interface Compilable { final void compile(); }
  3. C
    interface Compilable { static void compile(); }
  4. D
    interface Compilable { abstract void compile(); }
  5. E
    interface Compilable { protected abstract void compile (); }

Correct Answer:
AD

Question #23
Which is a key aspect of composition?
  1. A
    Using inheritance
  2. B
    Method delegation
  3. C
    Creating abstract classes
  4. D
    Implementing the composite interface

Correct Answer:
B
In the composition approach, the subclass becomes the "front-end class," and the superclass becomes the "back-end class." With inheritance, a subclass automatically inherits an implemenation of any non-private superclass method that it doesn't override. With composition, by contrast, the front-end class must explicitly invoke a corresponding method in the back-end class from its own implementation of the method. This explicit call is sometimes called "forwarding" or
"delegating" the method invocation to the back-end object. Note: Composition means the same as:
* contains
* is part of
Note 2: As you progress in an object-oriented design, you will likely encounter objects in the problem domain that contain other objects. In this situation you will be drawn to modeling a similar arrangement in the design of your solution. In an object-oriented design of a Java program, the way in which you model objects that contain other objects is with composition, the act of composing a class out of references to other objects. With composition, references to the constituent objects become fields of the containing object. To use composition in Java, you use instance variables of one object to hold references to other objects.

Question #24
Given:

What two changes should you make to apply the DAO pattern to this class?
  1. A
    Make the Customer class abstract.
  2. B
    Make the customer class an interface.
  3. C
    Move the add, delete, find, and update methods into their own implementation class.
  4. D
    Create an interface that defines the signatures of the add, delete, find, and update methods.
  5. E
    Make the add, delete, and find, and update methods private for encapsulation.
  6. F
    Make the getName and getID methods private for encapsulation.

Correct Answer:
CD
C:The methods related directly to the entity Customer is moved to a new class.
D: Example (here Customer is the main entity):
public class Customer {
private final String id;
private String contactName;
private String phone;
public void setId(String id) { this.id = id; }
public String getId() { return this.id; }
public void setContactName(String cn) { this.contactName = cn;} public String getContactName() { return this.contactName; } public void setPhone(String phone) { this.phone = phone; } public String getPhone()
{ return this.phone; }
}
public interface CustomerDAO {
public void addCustomer(Customer c) throws DataAccessException; public Customer getCustomer(String id) throws DataAccessException; public List getCustomers() throws DataAccessException; public void removeCustomer(String id) throws DataAccessException; public void modifyCustomer(Customer c) throws
DataAccessException; }

Note: DAO Design Pattern -
*Abstracts and encapsulates all access to a data source *Manages the connection to the data source to obtain and store data *Makes the code independent of the data sources and data vendors (e.g. plain-text, xml, LDAP,
MySQL, Oracle, DB2)

Question #25
Which two are true about Singletons?
  1. A
    A Singleton must implement serializable.
  2. B
    A Singleton has only the default constructor.
  3. C
    A Singleton implements a factory method.
  4. D
    A Singleton improves a class's cohesion.
  5. E
    Singletons can be designed to be thread-safe.

Correct Answer:
CE

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