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Thread: Controlling individual threads

  1. #1
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    Default Controlling individual threads

    Hi, I am new to threads and have made a test program. The code is short. I am trying to control each thread. I am not sure if my method is right. Can someone please help? I can not find the answer in books or on the internet, though, it could be my own mindset. I am getting the following error:

    ############# Start javac output #########################
    exec: javac -g threadTest.java

    threadTest.java:13: cannot find symbol
    symbol : method getcalcDone()
    location: class java.lang.Thread
    while (t1.getcalcDone() == false); //This loop will run till thread 1 has made it's calculation.
    ^
    threadTest.java:21: cannot find symbol
    symbol : variable t1
    location: class threadTest
    t1.calc(5, 3); // This SHOULD add 5 and 3 together. Not sure if I can control individual threads like this.
    ^
    threadTest.java:22: cannot find symbol
    symbol : variable t1
    location: class threadTest
    t2.calc(t1.results, 10); // Add the results of the first calculation and 10 together.
    ^
    threadTest.java:22: cannot find symbol
    symbol : variable t2
    location: class threadTest
    t2.calc(t1.results, 10); // Add the results of the first calculation and 10 together.
    ^
    4 errors
    ############# End javac output #########################


    ############# Start Java Code #########################
    import java.util.*;
     
    public class threadTest extends Thread
    {
     
    	public static void main(String[] args) 
    	{
    		Thread t1 = new threadTest();
    		Thread t2 = new threadTest();
     
    		t1.start();
     
    		while (t1.getcalcDone() == false); //This loop will run till thread 1 has made it's calculation.
     
    		t2.start();		
     
    	}
     
    	public void run()
       {
    	   t1.calc(5, 3); // This SHOULD add 5 and 3 together. Not sure if I can control individual threads like this.
    		t2.calc(t1.results, 10); // Add the results of the first calculation and 10 together.
    	}
     
    }
     
     
    class Thread1 extends Thread
    {
       int a = 0;
    	int b = 0;
    	int results = 0;
    	boolean calcDone = false;
     
       public Thread1(int a, int b)
    	{
    	    this.a = a;
    		 this.b = b;
    	}
     
       void calc(int a, int b)
    	{
    	    results = a + b;
    		 calcDone = true;
    	}
     
       boolean getcalcDone()
    	{
    	    return calcDone;
    	}
    }
    ################## End Java Code #######################

    Thank you for any ideas.
    Youngstorm
    Last edited by youngstorm; October 18th, 2010 at 02:39 PM. Reason: Inserted code tags


  2. #2
    Administrator copeg's Avatar
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    Default Re: Controlling individual threads

    This isn't a thread problem per se but rather an accumulation of several syntax errors. First, you are abstracting the threadTest class to a Thread, which does not contain the methods you are calling. Second, threadTest class does not contain these methods, but Thread1 does. Thirdly, your t1/t2 variables in the threadTest.run method are out of scope.

  3. #3
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    Default Re: Controlling individual threads

    Thank you for taking the time to respond.

    First, you are abstracting the threadTest class to a Thread, which does not contain the methods you are calling. Second, threadTest class does not contain these methods, but Thread1 does.
    How do I go about properly using these methods?

    Thirdly, your t1/t2 variables in the threadTest.run method are out of scope.
    I;m not sure I really understand this part, as it relates to threads. If I move the thread creation statements out of main, I get more errors than before. The new ones are as follows.

    ######################

    threadTest.java:11: non-static variable t1 cannot be referenced from a static context
    t1.start();
    ^
    threadTest.java:13: non-static variable t1 cannot be referenced from a static context
    while (t1.getcalcDone() == false); //This loop will run till thread 1 has made it's calculation.

    ######################

    Again, I may be thinking about threads all wrong. Sorry if I'm causing utter confusion.

  4. #4
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    Default Re: Controlling individual threads

    Again, this isn't a thread issue, its a syntax and programming flow problem.

    threadTest t1 = new threadTest();
    This allows the reference t1 access to the methods in threadTest. This will not fix your problem however, since you cannot call the methods defined in the class Thread1 from a reference (t1).

    I suggest you read some beginning tutorials on the subjects of variable scope and how to define an object and write a class before diving into multi-threading.

  5. #5
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    Default Re: Controlling individual threads

    Thanks. I'll do that and have some already.

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