Question about java threads programming

Hi
I have to develop a program where I need to access data from database, but I need to it using multithreading, currently I go sequentially to each database to access data which is slow
I have a Vector called systemnames, this one has list of all the systems I need to access.
Here is my current code, some thing like this
Vector masterVector = new Vector();
GetData data = new GetData();
For(int i =0; i < systemnames.size(); i++)
masterVector.add(data.getData((String)systemnames.get(i));
public class GetData
private Vector getData(String ipaddress)
//process SQL here
return data;
how do i convert this to multithread application, so there will be one thread running for each system in vector, this is speed up the process of extracting data and displaying it
has any one done this kind of program, what are the precautions i need to take care of
Ashish

http://www.google.com/search?q=java+threads+tutorial&sourceid=opera&num=0&ie=utf-8&oe=utf-8
http://java.sun.com/docs/books/tutorial/essential/threads/
http://www.javaworld.com/javaworld/jw-04-1996/jw-04-threads.html
http://www.cs.clemson.edu/~cs428/resources/java/tutorial/JTThreads.html
http://www-106.ibm.com/developerworks/edu/j-dw-javathread-i.html
When you post code, please use [code] and [/code] tags as described in Formatting Help on the message entry page. It makes it much easier to read and prevents accidental markup from array indices like [i].

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Peter__Lawrey wrote:
google has lots of information on java threaded.
One thing java does is support biased locking. i.e. the thread which last locked an object can lock that object again faster.
This may explain the difference. [http://www.google.co.uk/search?q=java+usebiasedlocking]
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You're talking about a GUI, but there's nothing in that code which is putting events into the GUI update thread. You also say that nothing happens to the GUI until the CommandProcessor.Run() method returns if you wait for the process.
This implies that you're calling CommandProcessor.Run() in an ActionListener. This will block the GUI thread until it completes.
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Edited by: 927494 on 13.04.2012 07:02
Edited by: 927494 on 13.04.2012 09:10

Thank you guys for the replies. I still have some more doubts :-)
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 // Call pre-existing constructor with default points, category and difficulty
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 * @param answer The correct answer for this question
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 return answerIsCorrect(userAnswer); // Call previously-defined version
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 public int getPointsEarned(boolean useNoBSRule)
System.out.println("useNoBS: " + useNoBSRule + "\tuserAnswer: " + userAnswer + "\tcorrectAnswer: " + correctAnswer);
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 instructions = instr;
 questions = new ArrayList<TrueFalseQuestion>(); //[MAX_NUMBER_OF_QUESTIONS];
 public String getInstructions()
 return instructions;
 public int getScore()
 return scoreEarned;
 public void addQuestion (TrueFalseQuestion q)
 scorePossible += q.getPointsValue();
 questions.add(q); // Automatically append question to end of test
 public String displayQuestion (int position)
 if (position < questions.size())
 return (position+1) + ". " + questions.get(position).getQuestion();
 else
 return null;
 public String displayTest ()
 String result = "";
 for (int i = 0; i < questions.size(); i++)
 result += (i+1) + ". (";
 TrueFalseQuestion t = questions.get(i);
 result += t.getPointsValue();
 result += " points)\n\n" + displayQuestion(i);
 result += "\n\n";
 return result;
 // Get test length (number of questions)
 public int length ()
 return questions.size();
 // Submit answer to a specific question
 public boolean answer(int number, String a)
 // Question numbers run from 0-(max-1) -- THIS WAS AN OFF-BY-ONE ERROR AT FIRST
 if (number >= 0 && number < questions.size())
 TrueFalseQuestion t = questions.get(number);
 t.submitAnswer(a);
 return true; // Question was answered
 else
 return false; // Unable to answer (nonexistent) question
 // Score exam
 public void scoreExam (boolean useNoBS)
 scoreEarned = 0;
 for (int i = 0; i < questions.size(); i++) // For each question in exam
 TrueFalseQuestion t = questions.get(i); // get current question
 scoreEarned += t.getPointsEarned(useNoBS);
}// Test harness for the Test and *Question classes
import java.util.*;
public class QuizDriver
 public static void main(String[] args)
 // Create a new Test object
 Test exam = new Test("Sample Exam", "Select the correct answer for each question");
 setUp(exam);
 Scanner sc = new Scanner(System.in);
 System.out.println(exam.getInstructions());
 // Administer exam
 for (int i = 0; i < exam.length(); i++)
 // Print out current question
 System.out.println(exam.displayQuestion(i));
 // Get user answer
 System.out.print("Your answer: ");
 String ans = sc.nextLine();
 if (ans.equals("")) // Handle blank responses for unanswered questions
 ans = null;
 exam.answer(i, ans);
 // Get exam results
 exam.scoreExam(true);
 System.out.println("Your final score was " + exam.getScore() + " points.");
 private static void setUp (Test t)
 TrueFalseQuestion x = new TrueFalseQuestion("The sky is blue.", "true", 2);
 t.addQuestion(x);
 x = new TrueFalseQuestion("The first FORTRAN compiler debuted in 1957", "true", 5);
 t.addQuestion(x);
 x = new TrueFalseQuestion("Spock was a Vulcan", "false", 3);
 t.addQuestion(x);
}This program is far from finishing.
I have many questions about this program, but let me ask this one first:
In the TrueFalseQeustion class, why are there so many constructors? What is the purpose of setting some of the variables to default values?
Thank you very much!!!
Edited by: Terry001 on Apr 16, 2008 10:02 AM

newark wrote:
Stop ignoring the error messages. You seem to think that an error message means you're doing the assignment wrong. It's probably a simple fix. Post the exact error messages, as well as the code that corresponds to them. The error message will tell you exactly what line the problem occurs on, so you know right where to look.Hi,
After some modifications, the program now gives me the result the assignment wants when I run it. But I still have trouble with the MultipleChoiceQuestion class
Here is the complete program
QuizDriver class
// Test harness for the Test and *Question classes
import java.util.*;
public class QuizDriver
 public static void main(String[] args)
 // Create a new Test object
 Test exam = new Test("Sample Exam", "Select the correct answer for each question");
 setUp(exam);
 Scanner sc = new Scanner(System.in);
 System.out.println(exam.getInstructions());
 // Administer exam
 for (int i = 0; i < exam.length(); i++)
 // Print out current question
 System.out.println(exam.displayQuestion(i));
 // Get user answer
 System.out.print("Your answer: ");
 String ans = sc.nextLine();
 if (ans.equals("")) // Handle blank responses for unanswered questions
 ans = null;
 exam.answer(i, ans);
 // Get exam results
 exam.scoreExam(true);
 System.out.println("Your final score was " + exam.getScore() + " points.");
 private static void setUp (Test t)
 Question x;
 x = new TrueFalseQuestion("The sky is blue.", "true", 2);
 t.addQuestion(x);
 x = new TrueFalseQuestion("The first FORTRAN compiler debuted in 1957", "true", 5);
 t.addQuestion(x);
 x = new TrueFalseQuestion("Spock was a Vulcan", "false", 3);
 t.addQuestion(x);
 x = new MultipleChoiceQuestion("What is the color of the car\na.Red\nb.Green", "a. Red", 3);
 t.addQuestion(x);
 x = new MultipleChoiceQuestion("What is the name of this class\na.CSE110\nb.CSE114", "b, CSE114", 3);
 t.addQuestion(x);
}Test
public class Test
 // Class constant
 public static final int MAX_NUMBER_OF_QUESTIONS = 10;
 // Class instance variables
 private String testName;
 private int scoreEarned; // What the student earned on the exam
 private int scorePossible; // Total point values of all questions
 private String instructions; // Exam header text
 private ArrayList<Question> questions; // Create inside constructor
 // Methods
 public Test (String name, String instr)
 testName = name;
 scoreEarned = 0;
 scorePossible = 0;
 instructions = instr;
 questions = new ArrayList<Question>(); //[MAX_NUMBER_OF_QUESTIONS];
 public String getInstructions()
 return instructions;
 public int getScore()
 return scoreEarned;
 public void addQuestion (Question q)
 scorePossible += q.getPointsValue();
 questions.add(q); // Automatically append question to end of test
 public String displayQuestion (int position)
 if (position < questions.size())
 return (position+1) + ". " + questions.get(position).getQuestion();
 else
 return null;
 public String displayTest ()
 String result = "";
 for (int i = 0; i < questions.size(); i++)
 result += (i+1) + ". (";
 Question t = questions.get(i);
 result += t.getPointsValue();
 result += " points)\n\n" + displayQuestion(i);
 result += "\n\n";
 return result;
 // Get test length (number of questions)
 public int length ()
 return questions.size();
 // Submit answer to a specific question
 public boolean answer(int number, String a)
 // Question numbers run from 0-(max-1) -- THIS WAS AN OFF-BY-ONE ERROR AT FIRST
 if (number >= 0 && number < questions.size())
 Question t = questions.get(number);
 t.submitAnswer(a);
 return true; // Question was answered
 else
 return false; // Unable to answer (nonexistent) question
 // Score exam
 public void scoreExam (boolean useNoBS)
 scoreEarned = 0;
 for (int i = 0; i < questions.size(); i++) // For each question in exam
 Question t = questions.get(i); // get current question
 scoreEarned += t.getPointsEarned(useNoBS);
}Question
public class Question
// Class constants
public static final int MIN_DIFFICULTY_LEVEL = 1;
public static final int MAX_DIFFICULTY_LEVEL = 5;
public static final int DEFAULT_DIFFICULTY_LEVEL = 1;
public static final int DEFAULT_POINT_VALUE = 1;
public static final String DEFAULT_CATEGORY_VALUE = "none";
// Class instance variables
protected String questionText;
protected String correctAnswer;
protected String userAnswer;
protected int pointsValue;
protected String category;
protected int difficultyLevel; //TODO: set a range for difficulty levels
// Constructors
public Question (String text, String answer, int pts, String ctgry, int level)
 questionText = text.trim();
 correctAnswer = answer.trim();
 userAnswer = null;
 if (pts >= 1)
 pointsValue = pts;
 else
 pointsValue = DEFAULT_POINT_VALUE;
 category = ctgry.trim();
 if (level >= MIN_DIFFICULTY_LEVEL && level <= MAX_DIFFICULTY_LEVEL)
 difficultyLevel = level;
 else
 difficultyLevel = DEFAULT_DIFFICULTY_LEVEL;
 // Overloaded (simplied) constructors
 public Question (String text, String answer, int pts)
 this(text, answer, pts, DEFAULT_CATEGORY_VALUE, DEFAULT_DIFFICULTY_LEVEL);
 public Question (String text, String answer, int pts, String ctgry)
 this(text, answer, pts, ctgry, DEFAULT_DIFFICULTY_LEVEL);
 public Question (String text, String answer, String ctgry)
 this(text, answer, DEFAULT_POINT_VALUE, ctgry, DEFAULT_DIFFICULTY_LEVEL);
 public Question (String text, String answer, int pts, int level)
 this(text, answer, pts, DEFAULT_CATEGORY_VALUE, level);
 // Methods
 public String getQuestion ()
 return questionText;
 // Use this method to store user answers
 public void submitAnswer (String ans)
 userAnswer = ans;
 public boolean answerIsCorrect (String userAns)
 if (userAns == null)
 return false;
 else
 // Normalize and compare answers
 char key = normalize (correctAnswer); //Get the first letter of an answer
 char ans = normalize (userAns); //Get the first letter of an answer
 return (key == ans);
 public boolean answerIsCorrect ()// Why do we need two answerisCorrect() methods?
 return answerIsCorrect (userAnswer);
 public int getPointsValue ()
 return pointsValue;
 public int getPointsEarned (boolean userNoBSRule)
 System.out.println ("useNoBS: " + userNoBSRule + "\tuseAnswer: " + userAnswer + "\tcorrectAnswer: " + correctAnswer);
 if (userNoBSRule && (userAnswer == null))
 return 1;
 else if (userAnswer == null)
 return 0;
 if (answerIsCorrect() == false)
 return 0;
 else
 return pointsValue;
 public String getCorrectAnswer ()
 return correctAnswer;
 public boolean hasBeenAnswered ()
 return (userAnswer != null);
 private char normalize (String input)
 if (input != null)
 input = input.trim();
 input = input.toLowerCase();
 return input.charAt(0);
 else
 return ' ';
 TrueFalseQuestion
public class TrueFalseQuestion extends Question
public TrueFalseQuestion (String text, String answer, int pts, String ctgry, int level)
 super(text, answer, pts, ctgry, level);
 public TrueFalseQuestion (String text, String answer, int pts)
 super(text, answer, pts, DEFAULT_CATEGORY_VALUE, DEFAULT_DIFFICULTY_LEVEL);
 public TrueFalseQuestion (String text, String answer, int pts, String ctgry)
 super(text, answer, pts, ctgry, DEFAULT_DIFFICULTY_LEVEL);
 public TrueFalseQuestion (String text, String answer, String ctgry)
 super(text, answer, DEFAULT_POINT_VALUE, ctgry, DEFAULT_DIFFICULTY_LEVEL);
 public TrueFalseQuestion (String text, String answer, int pts, int level)
 super(text, answer, pts, DEFAULT_CATEGORY_VALUE, level);
 // Methods
 public String[] getPossibleAnswerChoice ()
 String[] possibleAnswerChoice = {"true", "false"};
 return possibleAnswerChoice;
} MultipleChoiceQuestion
public class MultipleChoiceQuestion extends Question
 public MultipleChoiceQuestion (String text, String answer, int pts, String ctgry, int level)
 super(text, answer, pts, ctgry, level);
 public MultipleChoiceQuestion (String text, String answer, int pts)
 super(text, answer, pts, DEFAULT_CATEGORY_VALUE, DEFAULT_DIFFICULTY_LEVEL);
 public MultipleChoiceQuestion (String text, String answer, int pts, String ctgry)
 super(text, answer, pts, ctgry, DEFAULT_DIFFICULTY_LEVEL);
 public MultipleChoiceQuestion (String text, String answer, String ctgry)
 super(text, answer, DEFAULT_POINT_VALUE, ctgry, DEFAULT_DIFFICULTY_LEVEL);
 public MultipleChoiceQuestion (String text, String answer, int pts, int level)
 super(text, answer, pts, DEFAULT_CATEGORY_VALUE, level);
 // Methods
 String possibleAnswers;
 public String getPossibleAnswers ()
 return possibleAnswers;
 public void addAnswerChoice (String answerChoice)
 String ansChoice = answerChoice;
 questionText += "\nansChoice";
 possibleAnswers = answerChoice;
 public void printAnswerChoice ()
 System.out.println (questionText);
} I don't understand why the assignment wants me to build a method in the MultpleChoiceQuestion class to store the potential answer choices, I can make the program display the potential answer choices by including them in the questionText as following in the QuizDriver class
Question x;
x = new MultipleChoiceQuestion("What is the color of the car\na.Red\nb.Green", "a. Red", 3);
t.addQuestion(x); I don't know how to allow the client to construct the list of answer choices one at a time(add one potential answer choice by calling the addAsnwerChoices() method once)
Here are a few original sentences of my assignment which describe what I should do with the MultipleChoiceQuestion class
Using TrueFalseQuestion as a model, develop a new MultipleChoiceQuestion class that can be used to represent a problem where the user must select one of several answer choices (e.g., "Select answer (a), (b), (c), or (d)."). This new question type should have all of the same externally-visible functionality as TrueFalseQuestion, except that it must:
maintain a list of potential answer choices
provide a method that allows the client to construct the list of answer choices one at a time (i.e., the client should be able to call an addAnswerChoice() method to pass a new answer option to the MultipleChoiceQuestion.)
display (as part of the question text) the list of answer choices with appropriate letters ("abcd" instead of "0123") I don't understand what these sentences mean.
1. "Maintain a list of potential answer choices"-- this reminds me of the getPossibleAnswerChoice() method in the TrueFalseQuestion class
public String[] getPossibleAnswerChoice ()
 String[] possibleAnswerChoice = {"true", "false"};
 return possibleAnswerChoice;
 }I wonder that if the potential answer choices I have to store in the MultipleChoiceQuestion class are only letters "a", "b", "c", "d", etc, or include the answer text coming after the letters(eg. a.Red, b.Green)
2. "provide a method that allows the client to construct the list of answer choices one at a time". How do I achieve the functionality "one at a time"? Do I need to pass the input of the client (a potential answer choice) to the variable of the method which stores the list of potential answers?
3. "display (as part of the question text) the list of answer choices with appropriate letters". My question here is that: When the client type in one possible answer, should I append it to the variable questionText? (So I use the questionText variable in the methods of the first and second steps)
Thank you very much for your nice help!
Edited by: Terry001 on Apr 21, 2008 8:01 AM

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Despite the fact that everyone on the internet seems to say Official Java and ipad/ipad2 support will not happen,
I would like to press this issue a little further.
Is it yet possible to run a java.class file on ipad2,
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Edited by: 848439 on 25-Sep-2011 20:21

848439 wrote:
Despite the fact that everyone on the internet seems to say Official Java and ipad/ipad2 support will not happen,
I would like to press this issue a little further.You should listen to "everyone on the internet" this time. Give it up, Apple isn't going to allow it. Its either do what Apple instructs you to do, or take a hike (and switch to the Android platform).
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