Oracle 1Z0-804 Online Practice Questions and Exam Preparation

Oracle 1Z0-804 Online Questions & Answers

• Question 101:

  Given the code fragment:

  public void infected() {

  System.out.print("before ");

  try {

  int i = 1/0;

  System.out.print("try ");

  } catch(Exception e) {

  System.out.print("catch ");

  throw e;

  } finally {

  System.out.print("finally ");

  }

  System.out.print("after ");

  }

  What is the result when infected() is invoked?

  A. before try catch finally after
  B. before catch finally after
  C. before catch after
  D. before catch finally
  E. before catch
  C. before catch after

  ---

  The following line throws and exception: int i = 1/0;

  This exception is caught by: catch(Exception e) { System.out.print("catch "); throw e;

  Lastly, the finally statement is run as the finally block always executes when the try block exits. This ensures that the finally block is executed even if an unexpected exception occurs.

  Reference: Java Tutorial, The finally Block

• Question 102:

  Which two are true about Singletons?

  A. A Singleton must implement serializable.
  B. A Singleton has only the default constructor.
  C. A Singleton implements a factory method.
  D. A Singleton improves a class's cohesion.
  E. Singletons can be designed to be thread-safe.
  B. A Singleton has only the default constructor.
  E. Singletons can be designed to be thread-safe.

  ---

  B: The Singleton Pattern is one of the commonly used design templates when there needs to be a control on how an object can be created. This design pattern proposes that at any time there can only be one instance of a singleton (object) created by the JVM. The Singleton class's default constructor is made private, which prevents the direct instantiation of the object by others (Other Classes).

  E: The singleton pattern makes unit testing far more difficult, as it introduces global state into an application. It should also be noted that this pattern reduces the potential for parallelism within a program, because access to the singleton in a multi-threaded context must be serialised, e.g., by locking.

• Question 103:

  Given the code fragment:

  public class Test {

  public static void main(String[] args) {

  Path dir = Paths.get("D:\\company");

  //insert code here. Line ***

  for (Path entry: stream) {

  System.out.println(entry.getFileName());

  }

  } catch (IOException e) {

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

  }

  }

  Which two try statements, when inserted at line ***, enable you to print files with the extensions.java, .htm, and .jar.

  A. try (DirectoryStream stream = Files.newDirectoryStream(dir, "*. {java, htm, jar}")) {
  B. try (DirectoryStream stream = Files.newDirectoryStream(dir, "*. [java, htm, jar]")) {
  C. try (DirectoryStream stream = Files.newDirectoryStream(dir, "*. {java*, htm*, jar*}")) {
  D. try (DirectoryStream stream = Files.newDirectoryStream(dir, "**. {java, htm, jar}")) {
  A. try (DirectoryStream stream = Files.newDirectoryStream(dir, "*. {java, htm, jar}")) {
  D. try (DirectoryStream stream = Files.newDirectoryStream(dir, "**. {java, htm, jar}")) {

  ---

  "*. {java, htm, jar} and "**. {java, htm, jar} will match any file with file endings java, htm, or jar.

• Question 104:

  Given:

  class Erupt implements Runnable {

  public void run() {

  System.out.print(Thread.currentThread().getName());

  }

  }

  public class Yellowstone {

  static Erupt e = Erupt();

  Yellowstone() { new Thread(e, "const").start(); } // line A

  public static void main(String[] args) {

  new Yellowstone();

  new Faithful().go();

  }

  static class Faithful {

  void go() { new Thread(e, "inner").start(); } // line B

  }

  }

  What is the result?

  A. Both const and inner will be in the output.
  B. Only const will be in the output.
  C. Compilation fails due to an error on line A.
  D. Compilation fails due to an error on line B.
  E. An exception is thrown at runtime.
  A. Both const and inner will be in the output.

  ---

  The code compiles fine.

  Note: The Runnable interface should be implemented by any class whose instances are intended to be executed by a thread. The class must define a method of no arguments called run.

  This interface is designed to provide a common protocol for objects that wish to execute code while they are active. For example, Runnable is implemented by class Thread. Being active simply means that a thread has been started and has

  not yet been stopped.

  In addition, Runnable provides the means for a class to be active while not subclassing Thread. A class that implements Runnable can run without subclassing Thread by instantiating a Thread instance and passing itself in as the target. In

  most cases, the Runnable interface should be used if you are only planning to override the run() method and no other Thread methods. This is important because classes should not be subclassed unless the programmer intends on modifying

  or enhancing the fundamental behavior of the class.

  Note 2: start()

  Causes this thread to begin execution; the Java Virtual Machine calls the run method of this thread.

  Reference: java.lang

  Interface Runnable

• Question 105:

  Which four are syntactically correct?

  A. package abc; package def; import Java.util . * ; public class Test { }
  B. package abc; import Java.util.*; import Java.util.regex.* ; public class Test { }
  C. package abc; public class Test {} import Java.util.* ;
  D. import Java.util.*; package abc; public class Test {}
  E. package abc; import java.util. *; public class Test{}
  F. public class Test{} package abc; import java.util.*{}
  G. import java.util.*; public class Test{}
  H. package abc; public class test
  B. package abc; import Java.util.*; import Java.util.regex.* ; public class Test { }
  E. package abc; import java.util. *; public class Test{}
  G. import java.util.*; public class Test{}
  H. package abc; public class test

• Question 106:

  Given:

  interface Event {

  String getCategory();

  }

  public class CueSports {

  public String getCategory() {

  return "Cue sports";

  }

  }

  public class Snooker extends CueSports implements Event { // Line 9

  public static void main(String[] args) { Event obj1 = new Snooker(); // Line 11

  CueSports obj2 = new Snooker(); // Line 12

  System.out.print(obj1.GetCategory() + ", " + obj2.getCategory());

  }

  }

  What is the result?

  A. Cue sports, Cue sports
  B. Compilation fails at line 9
  C. Compilation fails at line 11
  D. Compilation fails at line 12
  E. Compilation fails at line 13
  B. Compilation fails at line 9

  ---

  Class Snooker is public. Should be declared in a separate file.

• Question 107:

  Which is a key aspect of composition?

  A. Using inheritance
  B. Method delegation
  C. Creating abstract classes
  D. Implementing the composite interface
  B. Method delegation

  ---

  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 108:

  Given the code fragment:

  public void otherMethod() {

  printFile("");

  }

  public void printFile(String file) {

  try (FileInputStream fis = new FileInputStream(file)) {

  System.out.println (fis.read());

  } catch (IOException e) {

  A. printStackTrace(); } Why is there no output when otherMethod is called?
  B. An exception other than IOException is thrown.
  C. Standard error is not mapped to the console.
  D. There is a compilation error.
  E. The exception is suppressed.
  D. There is a compilation error.

  ---

  The code compiles fine

  The line

  FileInputStream fis = new FileInputStream(file)) will fail at runtime since file is an empty string.

  Note:

  public void printStackTrace()

  Prints this throwable and its backtrace to the standard error stream.

• Question 109:

  Select four examples that initialize a NumberFormat reference using a factory.

  A. NumberFormat nf1 = new DecimalFormat();
  B. NumberFormat nf2 = new DecimalFormat("0.00") ;
  C. NumberFormat nf3 = NumberFormat.getInstance();
  D. NumberFormat nf4 = NumberFormat.getIntegerInstance();
  E. NumberFormat nf5 = DecimalFormat.getNumberInstance ();
  F. NumberFormat nf6 = Number Format.getCurrecyInstance () ;
  C. NumberFormat nf3 = NumberFormat.getInstance();
  D. NumberFormat nf4 = NumberFormat.getIntegerInstance();
  E. NumberFormat nf5 = DecimalFormat.getNumberInstance ();
  F. NumberFormat nf6 = Number Format.getCurrecyInstance () ;

  ---

  getInstance

  public static final NumberFormat getInstance()

  Returns the default number format for the current default locale. The default format is one of the styles provided by the other factory methods: getNumberInstance (E), getIntegerInstance (D), getCurrencyInstance (F) or getPercentInstance.

  Exactly which one is locale dependant.

  C: To obtain a NumberFormat for a specific locale, including the default locale, call one of NumberFormat's factory methods, such as getInstance().

  E: To obtain standard formats for a given locale, use the factory methods on NumberFormat such as getNumberInstance. These factories will return the most appropriate sub-class of NumberFormat for a given locale.

  F: To obtain standard formats for a given locale, use the factory methods on NumberFormat such as getInstance or getCurrencyInstance. Reference: java.text Class NumberFormat

• Question 110:

  Given the existing destination file, a source file only 1000 bytes long, and the code fragment:

  public void process (String source, String destination) { try (InputStream fis = new FileInputStream(source); OutputStream fos = new FileOutputStream(destination)

  ) {

  byte [] buff = new byte[2014];

  int i;

  while ((i = fis.read(buff)) != -1) {

  fos.write(buff,0,i); // line ***

  }

  } catch (IOException e) {

  System.out.println(e.getClass());

  }

  }

  What is the result?

  A. Overrides the content of the destination file with the source file content
  B. Appends the content of the source file to the destination file after a new line
  C. Appends the content of the source file to the destination file without a break in the flow
  D. Throws a runtime exception at line ***
  A. Overrides the content of the destination file with the source file content

  ---

  The whole of the FileInputStream will be read (see ** below).

  The content of the FileInputStream will overwrite the destination file (see *** below).

  * A FileInputStream obtains input bytes from a file in a file system. What files are available depends on the host environment.

  FileInputStream is meant for reading streams of raw bytes such as image data. For reading streams of characters, consider using FileReader.

  ** FileInputStream.read (byte[] b)

  Reads up to b.length bytes of data from this input stream into an array of bytes.

  Parameters:

  b - the buffer into which the data is read.

  Returns:

  the total number of bytes read into the buffer, or -1 if there is no more data because the end of the file has been reached.

  *** FileOutputStream

  You can construct a FileOutputStream object by passing a string containing a path name or a File object.

  You can also specify whether you want to append the output to an existing file.

  public FileOutputStream (String path)

  public FileOutputStream (String path, boolean append)

  public FileOutputStream (File file)

  public FileOutputStream (File file, boolean append)

  With the first and third constructors, if a file by the specified name already exists, the file will be overwritten. To append to an existing file, pass true to the second or fourth constructor.

  Reference: Class FileInputStream

  Reference: Class FileOutputStream