multithreading - Java thread program not working using wait() and notifyAll() -

below program. thread 0 gets printer, other threads not it. there 1 printer object, , want multiple job threads use printer. how make program work jobs printer. me code flow seems fine. synchronizing on single printer object. please help.

    package classestesting;      public class printerqueue {          final static printer printer = new printer();;          public static void main(string[] args) {             // todo auto-generated method stub             system.out.println("in main");              (int = 0; < 5; i++) {                 new thread(new jobs(), "thread - " + i).start();                 system.out.println("started " + + " thread");             }          }      }      class printer {         private boolean isused;          printer() {             this.isused = false;         }          public void setused(boolean used) {             this.isused = used;         }          public boolean isused() {              return this.isused;         }     }      class jobs implements runnable {          string name;         boolean isdataavailble;          jobs() {                     this.isdataavailble = true;         }          public void setnodata(boolean nodata) {             this.isdataavailble = false;         }          @override         public void run() {              while (isdataavailble) {                  if (printerqueue.printer.isused()) {                     try {                         system.out.println(thread.currentthread()                                 + "waiting printer");                         synchronized (printerqueue.printer) {                             printerqueue.printer.wait();                         }                     } catch (interruptedexception e) {                         e.printstacktrace();                     }                  } else {                     synchronized (printerqueue.printer) {                         system.out.println(thread.currentthread() + "got printer");                         printerqueue.printer.setused(true);                         try {                             thread.sleep(3000);                         } catch (interruptedexception e) {                             e.printstacktrace();                         }                         printerqueue.printer.setused(false);                         printerqueue.printer.notify();                     }                 }             }              try {                 thread.sleep(3000);             } catch (interruptedexception e) {                 e.printstacktrace();             }         }      } 

hi, have revised program getting lock first condition checking. thread 0 gets printer. other threads starve.

revised program:

    package classestesting;      public class printerqueue {          static printer printer;          public static void main(string[] args) {             // todo auto-generated method stub             system.out.println("in main");              printer = new printer();              (int = 0; < 5; i++) {                 jobs j1 = new jobs();                 j1.setprinter(printer);                  thread t1 = new thread(j1, "thread - " + i);                 t1.start();                  system.out.println("started " + + " thread");             }          }      }      class printer {         private boolean isused;          printer() {             this.isused = false;         }          public void setused(boolean used) {             this.isused = used;         }          public boolean isused() {              return this.isused;         }     }      class jobs implements runnable {          string name;         printer printer;          public printer getprinter() {             return printer;         }          public void setprinter(printer printer) {             this.printer = printer;         }          boolean isdataavailble;          jobs() {             this.isdataavailble = true;         }          public void setnodata(boolean nodata) {             this.isdataavailble = false;         }          @override         public void run() {              while (isdataavailble) {                 synchronized (printerqueue.printer) {                     if (this.printer.isused()) {                         try {                             system.out.println(thread.currentthread()                                     + "waiting printer");                              printerqueue.printer.wait();                          } catch (interruptedexception e) {                             e.printstacktrace();                         }                     }                      else {                          system.out.println(thread.currentthread() + "got printer");                          printerqueue.printer.setused(true);                          try {                             thread.sleep(3000);                         } catch (interruptedexception e) {                             e.printstacktrace();                         }                          printerqueue.printer.setused(false);                         printerqueue.printer.notify();                     }                 }             }          }      } 

if want resource available threads in fair manner, it's better use reentrantlock fair = true parameter. never rely on non-volatile variables changed in concurrent way. here's fixed code:

import java.util.concurrent.locks.lock; import java.util.concurrent.locks.reentrantlock;  public class printerqueue {     static printer printer;      public static void main(string[] args) {         system.out.println("in main");         printer = new printer();         (int = 0; < 5; i++) {             // added printer constructor parameter pass same printer             // jobs             new thread(new jobs(printer), "thread - " + i).start();             system.out.println("started " + + " thread");         }     } }  class printer {     // internally printer holds fair reentrantlock     lock lock = new reentrantlock(true);      // call printer     public void acquire() {         lock.lock();     }      // call release printer, it's available other threads     public void release() {         lock.unlock();     } }  class jobs implements runnable {     // declare isdataavailble volatile you're going change thread     volatile boolean isdataavailble;     private final printer printer;      // constructor takes printer argument     jobs(printer printer) {         this.isdataavailble = true;         this.printer = printer;     }      @override     public void run() {         try {             while (isdataavailble) {                 system.out.println(thread.currentthread()                         + "trying printer");                 // printer                 this.printer.acquire();                 try {                     system.out.println(thread.currentthread()                             + "printer acquired!");                     // use                     thread.sleep(3000);                 } {                     // release printer. better in block                     // release if unexpected exception occurs                     this.printer.release();                 }             }              thread.sleep(3000);         } catch (interruptedexception e) {             e.printstacktrace();         }     } }