Am new to android i dont know how to do that, Any one give the solution,
I have one main activity with button in that i have two fragments, by default one fragmnet is loaded, if i click a button default fragment need to hide and show another fragment , when i click back button in toolbar it needs to show default fragment. givew solution to that, thanks in advance
Just use fragment (support) manager to change fragments and override default onBackPressed() behaviour to do what you want. That's all you need.
In onBackPressed() method what can i do, if show as first fragment, then back button not working
What do you mean, the back button doesn't work? You activity should be able to handle it. Probably you are using the wrong handler.