Oracle 1Z0-804 Online Practice Questions and Exam Preparation

Oracle 1Z0-804 Online Questions & Answers

• Question 1:

  Given:

  public class CowArray extends Thread {

  static List myList = new CopyOnWriteArrayList();

  public static void main(String[] args) {

  myList.add(11);

  myList.add(22);

  myList.add(33);

  myList.add(44);

  new CowArray().start();

  for(Integer i: myList) {

  try { Thread.sleep(1000); }

  catch (Exception e) { System.out.print("e1 "); }

  System.out.print(" " +i);

  }

  }

  public void run() {

  try { Thread.sleep(500); }

  catch (Exception e) { System.out.print("e2 "); }

  myList.add(77);

  System.out.print("size: " + myList.size() + ", elements:");

  }

  }

  What is the most likely result?

  A. size: 4, elements: 11 22 33 44
  B. size: 5, elements: 11 22 33 44
  C. size: 4, elements: 11 22 33 44 77
  D. size: 5, elements: 11 22 33 44 77
  E. a ConcurrentModification Exception is thrown
  B. size: 5, elements: 11 22 33 44

• Question 2:

  Given these facts about Java classes in an application:

  -

  Class X is-a Class SuperX.

  -

  Class SuperX has-a public reference to a Class Z.

  -

  Class Y invokes public methods in Class Util.

  -

  Class X uses public variables in Class Util.

  Which three statements are true?

  A. Class X has-a Class Z.
  B. Class Util has weak encapsulation.
  C. Class Y demonstrates high cohesion.
  D. Class X is loosely coupled to Class Util.
  E. Class SuperX's level of cohesion CANNOT be determined
  B. Class Util has weak encapsulation.
  D. Class X is loosely coupled to Class Util.
  E. Class SuperX's level of cohesion CANNOT be determined

  ---

  B: Has class Util has both public methods and variables, it is an example of weak encapsulation.

  Note: Inheritance is also sometimes said to provide "weak encapsulation," because if you have code that directly uses a subclass, such as Apple, that code can be broken by changes to a superclass, such as Fruit. One of the ways to look at inheritance is that it allows subclass code to reuse superclass code. For example, if Apple doesn't override a method defined in its superclass Fruit, Apple is in a sense reusing Fruit's implementation of the method. But Apple only "weakly encapsulates" the Fruit code it is reusing, because changes to Fruit's interface can break code that directly uses Apple.

  D:

  Note: Tight coupling is when a group of classes are highly dependent on one another.

  This scenario arises when a class assumes too many responsibilities, or when one concern is spread over many classes rather than having its own class.

  Loose coupling is achieved by means of a design that promotes single-responsibility and separation of concerns.

  A loosely-coupled class can be consumed and tested independently of other (concrete) classes.

  Interfaces are a powerful tool to use for decoupling. Classes can communicate through interfaces rather than other concrete classes, and any class can be on the other end of that communication simply by implementing the interface.

  E: Not enough information regarding SuperX' to determine the level of cohesion.

• Question 3:

  Given the code fragment:

  public static void main(String[] args) {

  String source ="d:\\company\\info.txt";

  String dest ="d:\\company\\emp\\info.txt";

  // insert code fragment here. Line ***

  } catch (IOException e) {

  System.err.println("Caught IOException"+ e.getMessage());

  }

  }

  Which two try statements, when inserted at line ***, enable the code to successfully move the file info.txt to the destination directory, even if a file by the same name already exists in

  the destination directory?

  A. try (FileChannel in = new FileInputStream (source). getChannel(); FileChannel out = new FileOutputStream(dest).getChannel()) { in.transferTo(0, in.size(), out);
  B. try (Files.copy(Paths.get(source),Paths.get(dest)); Files.delete (Paths.get(source));
  C. try (Files.copy(Paths.get(source), Paths.get(dest),StandardCopyOption.REPLACE_Existing); Files.delete(Paths.get(source));
  D. try (Files.move(Paths.get(source), Paths.get(dest));
  E. try(BufferedReader br = Files.newBufferedReader(Paths.get(source), Charset.forName("UTF-8")); BufferedWriter bw = Files.newBufferedWriter(Paths.get(dest), Charset.forName("UTF-8")); String record = ""; while ((record = br.readLine()) ! = null) { bw.write(record); bw.newLine(); } Files.delete(Paths.get(source));
  C. try (Files.copy(Paths.get(source), Paths.get(dest),StandardCopyOption.REPLACE_Existing); Files.delete(Paths.get(source));
  E. try(BufferedReader br = Files.newBufferedReader(Paths.get(source), Charset.forName("UTF-8")); BufferedWriter bw = Files.newBufferedWriter(Paths.get(dest), Charset.forName("UTF-8")); String record = ""; while ((record = br.readLine()) ! = null) { bw.write(record); bw.newLine(); } Files.delete(Paths.get(source));

  ---

  C: Copies and overwrites the destination file (thanks to StandardCopyOption.REPLACE_Existing). Deletes the original file.

  E: By default the buffered writer replaces the existing file.This is what is needed in this scenario.

• Question 4:

  Given the code format:

  SimpleDateFormat sdf;

  Which code statements will display the full text month name?

  A. sdf = new SimpleDateFormat ("mm", Locale.UK); System.out.println("Result: ", sdf.format(new date()));
  B. sdf = new SimpleDateFormat ("MM", Locale.UK); System.out.println("Result: ", sdf.format(new date()));
  C. sdf = new SimpleDateFormat ("MMM", Locale.UK); System.out.println("Result: ", sdf.format(new date()));
  D. sdf = new SimpleDateFormat ("MMMM", Locale.UK); System.out.println("Result: ", sdf.format(new date()));
  D. sdf = new SimpleDateFormat ("MMMM", Locale.UK); System.out.println("Result: ", sdf.format(new date()));

  ---

  Typical output would be Current Month in M format : 2 Current Month in MM format : 02 Current Month in MMM format : Feb

  Current Month in MMMM format : February

• Question 5:

  Which two properly implement a Singleton pattern?

  A. class Singleton { private static Singleton instance; private Singleton () {} public static synchronized Singleton getInstance() { if (instance = = null) { instance = new Singleton (); } return instance; } }
  B. class Singleton { private static Singleton instance = new Singleton(); protected Singleton () {} public static Singleton getInstance () { return Instance; } }
  C. class Singleton { Singleton () {} private static class SingletonHolder { private static final Singleton INSTANCE = new Singleton (); } public static Singleton getInstance () { return SingletonHolder.INSTANCE; } }
  D. enum Singleton { INSTANCE; }
  A. class Singleton { private static Singleton instance; private Singleton () {} public static synchronized Singleton getInstance() { if (instance = = null) { instance = new Singleton (); } return instance; } }
  B. class Singleton { private static Singleton instance = new Singleton(); protected Singleton () {} public static Singleton getInstance () { return Instance; } }

  ---

  A: Here the method for getting the reference to the SingleTon object is correct.

  B: The constructor should be private such as:

  private static Singleton instance = new Singleton();

  Note: Java has several design patterns Singleton Pattern being the most commonly used.

  Java Singleton pattern belongs to the family of design patterns, that govern the instantiation process. This design pattern proposes that at any time there can only be one instance of a singleton (object) created by the JVM.

  The class's default constructor is made private, which prevents the direct instantiation of the object by others (Other Classes). A static modifier is applied to the instance method that returns the object as it then makes this method a class level method that can be accessed without creating an object.

• Question 6:

  Given the code fragment:

  public class Rank {

  static CopyOnWriteArraySet arr = new CopyOnWriteArraySet<>();

  static void verify() {

  String var ="";

  Iterator e=arr.iterator();

  while (e.hasNext()) {

  var = e.next();

  if(var.equals("A"))

  arr.remove(var);

  }

  }

  public static void main (String[] args) {

  ArrayList list1 = new ArrayList<>();

  list1.add("A"); list1.add("B");

  ArrayList list2 = new ArrayList<>();

  list1.add("A"); list1.add("D");

  arr.addAll(list1);

  arr.addAll(list2);

  verify();

  for(String var : arr)

  System.out.print(var + " ");

  }

  }

  What is the result?

  A. Null B D
  B. Null B null D
  C. B D
  D. D
  E. An exception is thrown at runtime
  C. B D

• Question 7:

  Given the following incorrect program:

  

  Which two changes make the program work correctly?

  A. Results must be retrieved from the newly created MyTask instances and combined.
  B. The threshold value must be increased so that the overhead of task creation does not dominate the cost of computation.
  C. The midpoint computation must be altered so that it splits the workload in an optimal manner.
  D. The compute () method must be changed to return an Integer result.
  E. The compute () method must be enhanced to (fork) newly created tasks.
  F. The myTask class must be modified to extend RecursiveAction instead of RecursiveTask
  A. Results must be retrieved from the newly created MyTask instances and combined.
  C. The midpoint computation must be altered so that it splits the workload in an optimal manner.

  ---

  Incorrect answer:

  F: A RecursiveAction is a recursive resultless ForkJoinTask. Here we need a result, so we should use a RecursiveTask.

• Question 8:

  Which two code blocks correctly initialize a Locale variable?

  A. Locale loc1 = "UK";
  B. Locale loc2 = Locale.getInstance("ru");
  C. Locale loc3 = Locale.getLocaleFactory("RU");
  D. Locale loc4 = Locale.UK;
  E. Locale loc5 = new Locale("ru", "RU");
  D. Locale loc4 = Locale.UK;
  E. Locale loc5 = new Locale("ru", "RU");

  ---

  D: The Locale class provides a number of convenient constants that you can use to create Locale objects for commonly used locales. For example, the following creates a Locale object for the United States: Locale.US

  E: Create a Locale object using the constructors in this class:

  Locale(String language)

  Locale(String language, String country)

  Locale(String language, String country, String variant)

  Reference: java.util Class Locale

• Question 9:

  Given:

  Which three are true?

  A. BasicCar uses composition.
  B. SuperCar uses composition.
  C. BasicCar is-a Car.
  D. SuperCar is-a Car.
  E. SuperCar takes advantage of polymorphism
  F. BasicCar has-a Car
  B. SuperCar uses composition.
  C. BasicCar is-a Car.
  E. SuperCar takes advantage of polymorphism

  ---

  B: The relationship modeled by composition is often referred to as the "has-a" relationship. Here SuperCar has-a Car.

  C: The relationship modeled by inheritance is often referred to as the "is-a" relationship.

  Modeling an is-a relationship is called inheritance because the subclass inherits the interface and, by default, the implementation of the superclass. Inheritance of interface guarantees that a subclass can accept all the same messages as its

  superclass. A subclass object can, in fact, be used anywhere a superclass object is called for.

  E: The polymorphic method call allows one type to express its distinction from another, similar type, as long as they're both derived from the same base type. This distinction is expressed through differences in behavior of the methods that

  you can call through the base class.

• Question 10:

  Given the interface:

  Public interface Idgenerator {

  int getNextId();

  }

  Which class implements IdGenerator in a thread-safe manner, so that no threads can get a duplicate id value current access?

  A. Public class generator Implements IdGenerator { Private AtomicInteger id = new AtomicInteger (0); return id.incrementAndget(); } }
  B. Public class Generator Implements idGenerator { private int id = 0; return ++id; } }
  C. Public class Generator Implements IdGenerator { private volatile int Id = 0; return + + Id; }
  D. Public class Generator Implements IdGenerator { private int id = 0; public int getNextId() { synchronized (new Generator()) { return + + id; } } }
  E. Public class Generator Implements IdGenerator { private int id = 0; public int getnextId() { synchronized (id) { return + + id; } } }
  D. Public class Generator Implements IdGenerator { private int id = 0; public int getNextId() { synchronized (new Generator()) { return + + id; } } }

  ---

  Code that is safe to call by multiple threads simultanously is called thread safe. If a piece of code is thread safe, then it contains no race conditions. Race condition only occur when multiple threads update shared resources. Therefore it is important to know what resources Java threads share when executing.

  In Java you can mark a method or a block of code as synchronized. Synchronized blocks can be used to avoid race conditions.