Programmatically switching off Android phone

Can we switch off an Android phone programmatically?

I am using following snippet but it didn't work for me.

KeyguardManager keyguardManager = (KeyguardManager) getSystemService(Activity.KEYGUARD_SERVICE); 
KeyguardLock lock = keyguardManager.newKeyguardLock(KEYGUARD_SERVICE); 

lock.disableKeyguard(); // to disable

lock.reenableKeygaurd();// to enable

and I used the permission also.