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

Question

我正在学习 Java 2 类(class)，我们的任务是展示如何为多个线程分配不同的优先级。

我正在尝试操作书中的示例代码以查看它是否有效，但出现编译器错误:无法在 TaskExecutor.java 中找到行的符号:

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

我的主要问题是:为什么我会收到“找不到符号”错误？如果我尝试就会发生

task1.setPriority(MIN_PRIORITY);

或

task1.setPriority(1);

还有。

我意识到某些代码可能是错误的，但它可以正常编译，除了 TaskExecutor.java 之外，它会抛出我上面提到的错误的三个实例，每个“任务”一个。我是一个视觉学习者，如果我可以尝试一些代码并弄清楚它们如何组合在一起，我可以学得更好，如果这证明了我的任何错误是合理的，哈哈。

Answer 1

您的PrintTask实现了Runnable。您想要调用 Thread 中定义的方法。

您无权访问在Executor内运行的线程，因此您无法设置它们的优先级。相反，创建常规线程，您可以设置它们的优先级。