How to use boolean in the Java?

Check this
http://en.wikipedia.org/wiki/Boolean_data_type[^]

From wiki:

In computer science, the Boolean or logical data type is a data type, having two values (usually denoted true and false), intended to represent the truth values of logic and Boolean algebra.

As stated above, boolean is for two values things(true/false).
For example, if you want to check the status of something like IsActive, IsAdmin, IsNegativeStock, IsEmpty, IsFull, etc.,
See the sample one below.

bool bAdmin;

public void SomeMethod()
{
  bAdmin = IsAdmin();
}
public bool IsAdmin()
{
//Code for checking the user is admin or not
//true - Admin user, false - Normal user
}

In your case, Gender is not suitable for boolean. Following are values for Gender field.

Male
Female
Transgender(Transman, Transwomen)
Unspecified
etc.,(I forgot one more value)

I have seen few websites that showing Gender dropdown with above mentioned values so Gender is not suitable for boolean.
In database side, I don't use bit datatype, instead I use someother datatype like char or int depends upon data. Because in past, we have used bit datatype for some columns but in one situation end user wanted to store some more values, so we had to use some other data type.