Android : Methods vs Method assigned to variables in Java

I'm sort of confused, I guess this question is just a matter of preference, I just want to understand the difference of the following code.

if (IsRegistered() == true) ...

public boolean IsRegistered()
{
 private boolean status = false;
 // blah blah code here
 return status;
}

vs

isRegistered = IsRegistered();
if (isRegistered)

I know both would work, I'm not being pedantic but I just want to understand so I would know my way around.