sleep() suspends the current thread for a given duration. After the time expires, the thread resumes automatically.

Definition List

• sleep(): Static Thread method that pauses the current thread.
• Sleeping Thread: Inactive thread waiting for sleep to expire.
• InterruptedException: Thrown when a sleeping thread is interrupted.
• Current Thread: The thread currently executing code.

sleep() Syntax

// Pause for milliseconds
Thread.sleep(milliseconds);

// Example — pause for 1 second
Thread.sleep(1000);

Thread State During sleep()

Runnable
    ↓
Timed Waiting (sleep)
    ↓
Runnable

Example 01: Using sleep() Method

package com.java.Multi_threading;

public class SleepExample {

    public static void main(String[] args) {

        for (int i = 1; i <= 5; i++) {

            System.out.println("Countdown: " + i);

            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

        System.out.println("Time's up!");
    }
}

Output

Countdown: 1
Countdown: 2
Countdown: 3
Countdown: 4
Countdown: 5
Time's up!

Handling InterruptedException

try {
    Thread.sleep(1000);
} catch (InterruptedException e) {
    e.printStackTrace();
}

sleep() vs wait()

• sleep() — Thread class. Does not release locks.
• wait() — Object class. Releases lock. Needs synchronization.
• Both throw InterruptedException.
• sleep() pauses; wait() coordinates thread communication.

Best Practices

• Keep sleep durations reasonable.
• Always handle InterruptedException.
• Don't use sleep() for synchronization.
• Account for system-dependent sleep variance.

FAQ

1. What does sleep() do in Java?

Pauses the current thread for a specified time.

2. Which thread does sleep() affect?

Only the currently executing thread.

3. Why does sleep() throw InterruptedException?

Another thread interrupted it during sleep.