Not able to lock android phone programmatically

Question

I have been trying to lock my phone programmatically when some particular condition is met. In my case a for loop which loops for 10 times.

Here's what I am doing to lock my phone

private DevicePolicyManager mDevicePolicyManager; 
private ComponentName mComponentName;  

In my onCreate:

mDevicePolicyManager = (DevicePolicyManager) getSystemService(Context.DEVICE_POLICY_SERVICE);
mComponentName = new ComponentName(this, AppAdminReceiver.class);

KeyguardManager keyGuardManager = (KeyguardManager) getSystemService(Context.KEYGUARD_SERVICE);
lock = keyGuardManager.newKeyguardLock(KEYGUARD_SERVICE);
lock.disableKeyguard();

In one of my func when the for loop loops for 10 times this get executed

lock.reenableKeyguard();
mDevicePolicyManager.lockNow();

But it does'nt seem to work. Can some one help me? And also the KeyGuardLock class has been deprecated I guess. Is there any other way ?