java - reason of IllegalMonitorStateException if I use wait within sync block -

I try to understand Java core synchronization.

I wrote a code sample:

write program

left right

10 times

  package concurrency; Public square LeftRightWaitNotifyExample {last fixed string str = "1"; Public static zero main (string [] Args) {New LeftLegThread (str). Start (); New RightLegThread (str) Start (); }} Class LeftLegThread thread {String Monitor} extends; Public LeftLegThread (string str) {monitor = str; } @ Override Public Zero Run () {try} {makeStep (); } Grip (Interrupted ejection) {// TODO Auto-Generated Catch Block e.printStackTrace (); }} Private Zero makeStep () throws interruptedException {synchronize (monitors) {for (int i = 0; i & lt; 10; i ++) {println ("left"); stop(); }}}} Class extends the RightLegThread thread {String Monitor}; Public RightLegThread (string str) {monitor = str; } @ Override Public Zero Run () {try} {makeStep (); } Grip (Inhibited Aspen E) {}} Private Weed Mastep (Interrupted Interrupted Expressions) {Synchronize} {while (true) {System.out.println ("right"); Notify(); stop(); }}}}   
 I get this output:  
  left-right thread "thread-0" java.lang at java.lang.IllegalMonitorStateException . Object.wait (native resident method) java.lang.Object.wait (object.java:485) concurrency.LeftLegThread.makeStep (LeftRightWaitNotifyExample.java35) at concurrency.LeftLegThread.run at (LeftRightWaitNotifyExample.java:23) exception At the Concurrency Right-Thread- / Code>  
 When I did not use the  wait  method under the  synchronized  block, before that That I found this error. But here I use waiting within the  synchronize  block  
, what is the cause of the problem and how it is decided?  
 Update  
 I rewrite the code as advised:  
  public class LeftRightWaitNotifyExample {last fixed string str = "1"; Public static zero principal (string [] ARGs throws interrupted expression (new left legTrade (str). Start (); Thread.Sleep (100); New RightLegThread (str) Start (); }} Class LeftLegThread thread {String Monitor} extends; Public LeftLegThread (string str) {monitor = str; } @ Override Public Zero Run () {try} {makeStep (); } Grip (Interrupted ejection) {// TODO Auto-Generated Catch Block e.printStackTrace (); }} Private Zero makeStep throws interruptedException {synchronize (for {{int i = 0; i & lt; 2; i ++) {println ("left"); Monitor.wait (); Monitor.notify (); }}}} Class extends the RightLegThread thread {String Monitor}; Public RightLegThread (string str) {monitor = str; } @ Override Public Zero Run () {try} {makeStep (); } Grip (Inhibited Aspen E) {}} Private Weed Mastep (Interrupted Interrupted Expressions) {Synchronize} {while (true) {System.out.println ("right"); Monitor.notify (); Monitor.wait (); Current} <>   
 current output:  
  left right alright right   
 why  right < / Code> Boycott 3 But  Left  Why only two times?   
 
 
 You are syncing on  monitor , so you  wait ()  on the monitor, also:  
  monitor. Wait ();   
 Right now you are waiting on  this , which is not the monitor owner, because there is a synchronization  monitor . > 
 Note that definitely  notify  should also be done on the  monitor  object and that you  notify  >  >  threads otherwise it may be that a thread is waiting for a missing notification. Using a timeout (overloaded version of  wait ) can also be a good idea to catch corner cases.