Default [q]How to get the present layout of an activity

I have used a command in an onclicklistener of button to change the layout without creating a new activity like this
setContentView(R.layout.myxml);

Now to i want to override onBackPressed so that
if layout is a changed one,it will first go to default layout ,then exit the app.
But how can i identify that which layout is currently set on the activity

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