[android] Check if EditText is empty.

with this short code you can delete empty space at start and end of the string. If the string is "" return the message "error" else you ave a string

EditText user = findViewById(R.id.user); 
userString = user.getText().toString().trim(); 
if (userString.matches("")) {
    Toast.makeText(this, "Error", Toast.LENGTH_SHORT).show();
    return; 
}else{
     Toast.makeText(this, "Ok", Toast.LENGTH_SHORT).show();
}