When can we call wait() and wait(long) methods of a Thread in Java?

This article will discuss the wait() and wait(long timeout) methods, along with a suitable example that explains when to call these methods in a thread in Java.

The wait() Method

In Java, the wait() method is used in multithreading and causes the current thread to "wait" until another thread calls notify() or notifyAll() on the same object. When the wait() method is called, the thread moves from the running to the waiting state and resumes only when notified, if not a deadlock will be formed.

Note: Call the wait() method only when the thread should wait without any time limit.

Following is the syntax of the Java Thread wait() method -

public final void wait() throws InterruptedException

Example

The following example shows a real-time use case of when to call the wait() method -

class MyRunnable implements Runnable {
   public void run() {
      synchronized(this) {
         System.out.println("In run() method");
         try {
            this.wait();
            System.out.println("Thread in waiting state, waiting for some other threads on same object to call notify() or notifyAll()");
         } catch (InterruptedException ie) {
            ie.printStackTrace();
         }
      }
   }
}
public class WaitMethodWithoutParameterTest {
   public static void main(String[] args) {
       MyRunnable myRunnable = new MyRunnable();
       Thread thread = new Thread(myRunnable, "Thread-1");
       thread.start();
   }
}

Following is the output of the above program -

In run() method

The wait(long timeout) Method

In Java, the wait(long timeout) causes the current thread to wait until either another thread invokes the notify() or notifyAll() methods for this object, or a specified timeout time has elapsed.

When wait(long timeout) is called on an object, the thread enters from running to waiting state, even if notify() or notifyAll() is not called after the timeout time has elapsed thread will go from waiting to runnable state.

Note: Call the wait(long timeout) method only when the thread should wait till the given time limit.

Following is the syntax of the Java Thread wait(long timeout) method -

public final void wait(long timeout) throws InterruptedException

Here, the timeout specifies the maximum time (in milliseconds) that the current thread should wait.

Example

class MyRunnable implements Runnable {
   public void run() {
      synchronized(this) {
         System.out.println("In run() method");
         try {
            this.wait(1000); 
            System.out.println("Thread in waiting state, waiting for some other threads on same object to call notify() or notifyAll()");
         } catch (InterruptedException ie) {
            ie.printStackTrace();
         }
      }
   }
}
public class WaitMethodWithParameterTest {
   public static void main(String[] args) {
      MyRunnable myRunnable = new MyRunnable();
      Thread thread = new Thread(myRunnable, "Thread-1");
      thread.start();
   }
}

Following is the output of the above program -

In run() method
Thread in waiting state, waiting for some other threads on same object to call notify() or notifyAll()

Difference between wait() and wait(long timeout) Method

Below are the difference between wait() and wait(long timeout) method -

• The wait() method waits indefinitely until notified, whereas the wait(long timeout) method waits until notified or until the specified timeout expires.
• The wait() method does not accept any timeout, whereas the wait(long timeout) method accepts a timeout value in milliseconds.
• The wait() method resumes only when another thread calls notify() or notifyAll(), whereas the wait(long timeout) method resumes either when notified or when the timeout is reached.