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Differences between wait() and join() methods in Java
In multithreading when we deal with threads there comes the requirement of pause and start a thread for this Threading provides two methods wait and join which are used for the same.
The following are the important differences between wait() and join().
| Sr. No. | Key | wait() | join() |
|---|---|---|---|
| 1 | Declaration | wait() method is defined in Object class and hence the wait() method is declared in java.lang package. | join() method, on the other hand, is also defined in java.lang package but in Thread class. |
| 2 | Usage | wait() method is primarily used for the inter-thread communication. | On the other hand join() is used for adding sequencing between multiple threads, one thread starts execution after first thread execution finished. |
| 3 | Counter method | As wait() method is used to pause the current thread so its counter method is also provided in object class to resume the thread which is notify() and notifyAll(). | On the other hand we can not break the waiting imposed by join() method without unless or interruption the thread on which join is called has execution finished. |
| 4 | Context | In order to call wait method we require synchronized block or method as if wait() method is called outside the synchronized context it will throw IllegalMonitorStateException. | On the other no such condition required for calling join() method and we can call join() method with and without synchronized context in Java.. |
| 5 | Lock Release | wait() releases the monitor or lock held on the object which wait is invoked on | On the other hand, calling join() method doesn't release any monitor or lock. |
Example of wait() vs join()
JavaTester.java
public class JavaTester extends Thread {
static Object lock = new Object();
static int n;
int i;
String name;
JavaTester(String name, int i) {
this.name = name;
this.i = i;
}
@Override
public void run() {
try {
synchronized (lock) {
while (i != n) {
lock.wait();
}
System.out.println(name + " started");
n++;
lock.notifyAll();
}
synchronized (lock) {
while (i != n - 4) {
lock.wait();
}
System.out.println(name + " finished");
n++;
lock.notifyAll();
}
}
catch (InterruptedException e) {
}
}
public static void main(String[] args) throws Exception {
new JavaTester("a", 0).start();
new JavaTester("b", 1).start();
new JavaTester("c", 2).start();
new JavaTester("d", 3).start();
}
}
Output
a started b started c started d started a finished b finished c finished d finished
Updated on: 2019-09-18T14:16:47+05:30
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