Fundamentals of Programming

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Fundamentals of Programming

• QA

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Last Week...

• Identified question types
• Answered questions based on fundamentals
• Overview of OO concepts and related questions in
  the model paper
• Gave contact information fp_at_ict.cmb.ac.lk

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This Week...

• Discuss briefly some strategies for answering
  questions
• Look at more model questions selected from other
  (more advanced) areas of the syllabus

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Strategies for Answering

• Fill-in-the-blank Usually 1 answer
• Expression evaluation Usually 1 answer
• Identifying correct/incorrect statements
• Note if correct or incorrect choices are required
• When combinations are given, there may still be
  more than one answer (try by elimination)
• When multiple answers are possible, at least mark
  those you are sure of (dont skip)
• This is NOT an exhaustive list of strategies!

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• There are some sections in the syllabus relating
  to more advanced features of Java
• One of these relates to threads and
  multi-threading
• Java threads have six states ready, running,
  waiting, sleeping, blocked and dead
• The init() method gives birth to a thread that
  becomes ready to be run. The run() method then
  takes the thread into running state.
• The sleep() method can stop a thread for a
  period, while the wait method makes a thread wait
  till it is woken using an explicit notify()
  method.
• Once a thread completes execution it dies.

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• The final event that can occur to a running
  thread is that it can be blocked for accessing
  input or output. It is unblocked after I/O is
  completed.
• Threads can be assigned pre-defined priorities,
  MIN, NORM and MAX or a customised priority level
  (1-10)
• Priority is implemented by higher priority
  threads pre-empting (taking the processor from)
  lower priority ones as soon as they become ready.
  
• While any thread can explicitly yield to another,
  by definition higher priority threads cannot do
  this to lower ones.

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• Since platforms are different, the exact way in
  which multi-threading is implemented on each may
  be slightly different

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• 49) Identify the correct statements related to
  threads?
• (a) A thread is not executable if it is dead.
• (b) In Java, a higher priority executable thread
  will pre-empt threads of lower priority.
• (c) Threads may yield to threads of lower
  priority.
• (d) Java multithreading is platform dependent.
  Thus, a multithreaded application could behave
  differently on different Java implementations.
  (e) Threads in the waiting state for a monitor
  object must eventually be awakened explicitly
  with a notify (or interrupt ) or the tread will
  wait forever
• ANSWER (a), (b), (d) and (e)

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• 17) Following are some descriptions about
  threads. Identify the correct statement(s).
• (a) Java is a multithreaded language that allows
  a program to have in-built processes where more
  than one process can be executed concurrently
  within a single program
• (b) Multithreading is similar to
  multiprocessing however with multithreading all
  execution context do not share the same memory.
• (c) The benefits of multithreading is most
  apparent in Graphical User Interfaces and in
  applets
• (d) In Java thread class is defined in java.lang
  as a subclass of the Object class
• (e) A thread is a non-independent sequential
  flow of control within a process.

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• This is another question regarding threads
• Multithreading is a technique of running more
  than a single independent thread of instruction
  within a single program
• In Java this support is available as part of the
  core language
• Multiprocessing is where each such process also
  has its own memory, but a Java program is one
  such process.
• Multithreading is essential for windows-based and
  internet/ web programming where more than one
  thing can be done at a time
• ANSWER (a), (c) and (d)

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• 37) The following descriptions are related to
  Input/Output in java. Identify the correct ones.
• a) Streams provide communication channels
  between files and programs.
• b) Random access file is useful for transaction
  processing applications such as airline
  reservation systems
• c) DataInputStream class supports seeking a
  specific byte position in the file with method
  seek.
• d) An existing file is opened for output the
  contents of the file are discarded after issuing
  a warning message.
• e) Not opening a file before attempting to
  reference it in a program will not give an error
  in java

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• This is a question regarding another of the more
  advanced features of Java - INPUT and OUTPUT
• Streams are an abstraction of all forms of
  information input and output - be it to/from a
  file, a device or a network
• There are various extensions of the basic Stream
  to handle different requirements
• e.g. RandomAccessFile is a file that can be
  searched non-sequentially (using the method seek)
  - an essential feature of any on-line system
• Unlike in some languages, opening an existing
  file for output does not discard its contents,
  but attempting to reference a file without
  opening it will result in an error
• ANSWER (a) and (b)

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• 50) The following descriptions are related to
  Javas Files and Streams. Identify the correct
  ones.
• (i) Java views each file as a sequential stream
  of bytes
• (ii) The InputStream class is an abstract class
  that serves as the base class for all other input
  stream classes.
• (iii) The PrintStream class is derived from
  OutputStream and is designed primarily for
  printing output data as text
• (iv) The DataInputStream class is useful for
  reading abstract Java data types from an input
  stream
• (a) all correct (b) (i), (ii) and (iii) (c) (i)
  and (iii)
• (d) (ii), (iii) (e) (i) ,(iv)

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• This is another question relating to Streams
• As discussed in the previous question a stream
  can be viewed as a channel for sending and
  receiving information
• The abstract classes InputStream and OutputStream
  are the basic classes for inputting and
  outputting information respectively using this
  channel concept
• These basic classes are extended for more
  functionality such as in DataInputStream and
  PrintStream respectively
• DataInputStream supports reading basic Java data
  types from streams, but it needs to be extended
  to handle abstract data types
• ANSWER (b) - i.e. all except the last is correct

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• Exam Dates 31st March and 1st April
• Wish you all success!