Why we need to use Thread.sleep() instead Sleep() in Java?

Question

Why we have to use Thread.sleep() instead of just sleep() in Java? What are reason, that forces developers to use "longer" version?

Answer 1

Because sleep() is a static method of Thread . You could import it static, and then use sleep()

import static java.lang.Thread.sleep;
public static void main( String[] args )
    {
        try
        {
            sleep( 1000 );
        }
        catch ( InterruptedException e )
        {
            e.printStackTrace();
        }
    }

see here: http://docs.oracle.com/javase/1.5.0/docs/guide/language/static-import.html

see also here ( https://stackoverflow.com/a/421127/461499 ) on why to use static imports sparelingly.

Answer 2

Java is an object oriented language - every method ("function") must belong to a class, even if it's a static method (consider, eg, that there's no "global" print function - you must call System.out.print ). If it really annoys you, though, you could statically import the method:

import static java.lang.Thread.sleep

public class MyClass {
    public static void main (String[] args) {
        sleep (10);
    }
}

Answer 3

sleep() method in Thread class is a static method. We don't access static methods using the instance object.

Both the this.sleep() and Thread.sleep() are the same but it's against the conventions.

static keyword means it's common to all the classes there for if you use an instance variable to access a static method it's not clear.