Java - Thread.setPriority() Error: cannot find symbol (the period between Thread and setPriority)

Question

I'm taking a Java 2 class and our assignment is to show how multiple threads can be assigned different priorities.

I'm trying to manipulate the example code in the book to see if it works and I'm getting a compiler error: cannot find symbol for lines in TaskExecutor.java:

setPriority(task1.MIN_PRIORITY);
setPriority(task2.MAX_PRIORITY);
setPriority(task3.NORMAL_PRIORITY);

PrintTask.java:

import java.util.Random;
import java.lang.*;

public class PrintTask implements Runnable {
    private final int sleepTime; // random sleep time for thread
    private final String taskName; // name of task
    private final static Random generator = new Random();

    // constructor
    public PrintTask( String name ) {
        taskName = name; // set task name
        // pick random sleep time between 0 and 5 seconds
        sleepTime = generator.nextInt( 5000 ); // milliseconds
    }

    // method run contains the code that a thread will execute
    public void run() {

        try { // put thread to sleep for sleepTime amount of time
            System.out.printf( 
                "%s going to sleep for %d milliseconds.\n", taskName, sleepTime );
            Thread.sleep( sleepTime ); // put thread to sleep
        }
        catch ( InterruptedException exception ) {
            System.out.printf( 
                "%s %s\n", taskName, "terminated prematurely due to interruption" );
        }

    // print task name
    System.out.printf( 
        "%s done sleeping\n", taskName );

    } // end method run
} // end class PrintTask

TaskExecutor.java:

import java.util.concurrent.Executors;
import java.util.concurrent.ExecutorService;
import java.lang.*;

public class TaskExecutor {
    public static void main( String[] args ) {
        // create and name each runnable
        PrintTask task1 = new PrintTask( "task1" );
        PrintTask task2 = new PrintTask( "task2" );
        PrintTask task3 = new PrintTask( "task3" );

        // Set Priorities
        setPriority(task1.MIN_PRIORITY); 
        setPriority(task2.MAX_PRIORITY);
        setPriority(task3.NORMAL_PRIORITY);
        /* compiler error: cannot find symbol  
                       setPriority(task_.---_PRIORITY);"
                                        ^
        */

        System.out.println( "Starting Executor" );

        // create ExecutorService to manage threads
        ExecutorService threadExecutor = Executors.newCachedThreadPool();

        // start threads and place in runnable state
        threadExecutor.execute( task1 ); // start task1
        threadExecutor.execute( task2 ); // start task2
        threadExecutor.execute( task3 ); // start task3

        // shut down worker threads when their tasks complete
        threadExecutor.shutdown();

        System.out.println( "Tasks started, main ends.\n" );

    } // end main
} // end class TaskExecutor

My main question is: Why am I getting the "cannot find symbol" error? It happens if I try

task1.setPriority(MIN_PRIORITY);

or

task1.setPriority(1);

as well.

I realize some of the code may be wrong, but it compiles alright except TaskExecutor.java, which throws up three instances of the error I mentioned above, one for each 'task'. I'm a visual learner and I can learn much better if I can play around with bits of code and figure out how they fit together, if that justifies any of my mistakes, haha.

Answer 1

As PrintTask implements Runnable and it doesnot extends Thread class you cannot call Thread class method

well you can do something like this

PrintTask task1 = new PrintTask( "task1" );
Thread th=new Thread(task1);
th.setPriority(Thread.MIN_PRIORITY);