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POUnderstanding the use of Synchronized
 

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    <p>I am trying to understand the use of Synchronized block. </p> <p>In the below program, Inside a produce and consumer method I have created a synchronized block and if I lock it by using lock1(object). I am getting the following error, why is this, why am i getting this error? </p> <p>I am aware that by replacing lock1 by this(same class). I can get rid of the error. I still want to know why this error as everything seems very logical to me.</p> <p>Program</p> <pre><code>import java.util.Scanner; public class Worker { private Object lock1 = new Object(); private Object lock2 = new Object(); public void produce() throws InterruptedException { synchronized (lock1) { System.out.println("Producer thread running"); wait(); System.out.println("Producer resumed"); } } public void consumer() throws InterruptedException { Scanner scanner = new Scanner(System.in); Thread.sleep(2000); synchronized (lock1) { System.out.println("Waiting for return key"); scanner.nextLine(); System.out.println("return key is pressed"); notify(); Thread.sleep(5000); System.out.println("Consumer is over"); } } public void main() { Thread t1 = new Thread(new Runnable() { public void run() { try { produce(); } catch (InterruptedException e) { e.printStackTrace(); } } }); Thread t2 = new Thread(new Runnable() { public void run() { try { consumer(); } catch (InterruptedException e) { e.printStackTrace(); } } }); t1.start(); t2.start(); try { t1.join(); t2.join(); } catch (InterruptedException e) { e.printStackTrace(); } } } </code></pre> <p><p></p> <pre><code>Exception in thread "Thread-0" java.lang.IllegalMonitorStateException at java.lang.Object.wait(Native Method) at java.lang.Object.wait(Object.java:503) at Worker.produce(Worker.java:14) at Worker$1.run(Worker.java:43) at java.lang.Thread.run(Unknown Source) </code></pre>
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