// Fig. 4.1: PrintTask.java 
 
// PrintTask class sleeps for a random time from 0 to 5 seconds 
 
import java.util.Random; 
 
  
 
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(); 
 
   
 
  public PrintTask( String name ) 
 
  { 
 
   taskName = name; // set task name 
 
     
 
   // pick random sleep time between 0 and 5 seconds 
 
   sleepTime = generator.nextInt( 5000 ); // milliseconds 
 
  } // end PrintTask constructor 
 
  
 
  // 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 
 
   } // end try     
 
   catch ( InterruptedException exception ) 
 
   { 
 
     System.out.printf( "%s %s\n", taskName, 
 
      "terminated prematurely due to interruption" ); 
 
   } // end catch 
 
     
 
   // print task name 
 
   System.out.printf( "%s done sleeping\n", taskName );  
 
  } // end method run 
 
} // end class PrintTask 

// Fig. 4.2 ThreadCreator.java 
 
// Creating and starting three threads to execute Runnables. 
 
import java.lang.Thread; 
 
  
 
public class ThreadCreator 
 
{ 
 
  public static void main( String[] args ) 
 
  { 
 
   System.out.println( "Creating threads" ); 
 
  
 
   // create each thread with a new targeted runnable 
 
   Thread thread1 = new Thread( new PrintTask( "task1" ) ); 
 
   Thread thread2 = new Thread( new PrintTask( "task2" ) ); 
 
   Thread thread3 = new Thread( new PrintTask( "task3" ) ); 
 
  
 
   System.out.println( "Threads created, starting tasks." ); 
 
  
 
   // start threads and place in runnable state 
 
   thread1.start(); // invokes task1抯 run method 
 
   thread2.start(); // invokes task2抯 run method 
 
   thread3.start(); // invokes task3抯 run method 
 
  
 
   System.out.println( "Tasks started, main ends.\n" ); 
 
  } // end main 
 
} // end class RunnableTester   
 

// Fig. 4.3: TaskExecutor.java 
// Using an ExecutorService to execute Runnables. 
import java.util.concurrent.Executors; 
import java.util.concurrent.ExecutorService; 
 
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" ); 
     
   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 

// Adds integers to an array shared with other Runnables 
 
import java.lang.Runnable; 
 
  
 
public class ArrayWriter implements Runnable 
 
{ 
 
  private final SimpleArray sharedSimpleArray; 
 
  private final int startValue; 
 
  
 
  public ArrayWriter( int value, SimpleArray array ) 
 
  { 
 
   startValue = value; 
 
   sharedSimpleArray= array; 
 
  } // end constructor 
 
  
 
  public void run() 
 
  { 
 
   for ( int i = startValue; i < startValue + 3; i++ ) 
 
   { 
 
     sharedSimpleArray.add( i ); // add an element to the shared array 
 
   } // end for 
 
  } // end method run 
 
} // end class ArrayWrite 

// Fig 5.2: SharedArrayTest.java 
 
// Executes two Runnables to add elements to a shared SimpleArray. 
 
import java.util.concurrent.Executors; 
 
import java.util.concurrent.ExecutorService; 
 
import java.util.concurrent.TimeUnit; 
 
  
 
public class SharedArrayTest 
 
{ 
 
  public static void main( String[] arg ) 
 
  { 
 
   // construct the shared object 
 
   SimpleArray sharedSimpleArray = new SimpleArray( 6 ); 
 
  
 
   // create two tasks to write to the shared SimpleArray 
 
   ArrayWriter writer1 = new ArrayWriter( 1, sharedSimpleArray ); 
 
   ArrayWriter writer2 = new ArrayWriter( 11, sharedSimpleArray ); 
 
  
 
   // execute the tasks with an ExecutorService 
 
   ExecutorService executor = Executors.newCachedThreadPool(); 
 
   executor.execute( writer1 ); 
 
   executor.execute( writer2 ); 
 
  
 
   executor.shutdown(); 
 
  
 
   try 
 
   { 
 
     // wait 1 minute for both writers to finish executing 
 
     boolean tasksEnded = executor.awaitTermination(  
 
      1, TimeUnit.MINUTES ); 
 
  
 
     if ( tasksEnded ) 
 
      System.out.println( sharedSimpleArray ); // print contents 
 
     else 
 
      System.out.println(  
 
        "Timed out while waiting for tasks to finish." ); 
 
   } // end try 
 
   catch ( InterruptedException ex ) 
 
   { 
 
     System.out.println(  
 
      "Interrupted while wait for tasks to finish." ); 
 
   } // end catch 
 
  } // end main 
 
} // end class SharedArrayTest 

// Fig.5.3 : SimpleArray.java 
 
// Class that manages an integer array to be shared by multiple  
 
// threads with synchronization. 
 
import java.util.Random; 
 
  
 
public class SimpleArray 
 
{ 
 
  private final int array[]; // the shared integer array 
 
  private int writeIndex = 0; // index of next element to be written 
 
  private final static Random generator = new Random(); 
 
  
 
  // construct a SimpleArray of a given size 
 
  public SimpleArray( int size ) 
 
  { 
 
   array = new int[ size ]; 
 
  } // end constructor 
 
  
 
  // add a value to the shared array 
 
  public synchronized void add( int value ) 
 
  { 
 
   int position = writeIndex; // store the write index 
 
  
 
   try 
 
   { 
 
     // put thread to sleep for 0-499 milliseconds 
 
     Thread.sleep( generator.nextInt( 500 ) );  
 
   } // end try 
 
   catch ( InterruptedException ex ) 
 
   { 
 
     ex.printStackTrace(); 
 
   } // end catch 
 
  
 
   // put value in the appropriate element 
 
   array[ position ] = value; 
 
   System.out.printf( "%s wrote %2d to element %d.\n",  
 
     Thread.currentThread().getName(), value, position ); 
 
  
 
   ++writeIndex; // increment index of element to be written next 
 
   System.out.printf( "Next write index: %d\n", writeIndex ); 
 
  } // end method add 
 
   
 
  // used for outputting the contents of the shared integer array 
 
  public String toString() 
 
  { 
 
   String arrayString = "\nContents of SimpleArray:\n"; 
 
   
 
   for ( int i = 0; i < array.length; i++ ) 
 
     arrayString += array[ i ] + " "; 
 
   
 
   return arrayString; 
 
  } // end method toString 
 
} // end class SimpleArray