Email validation on EditText - Android

I have an Email EditText and i want to check it using email validation.

This's my email validation code

public final static boolean isValidEmail(CharSequence target) {
    if (target == null) {
        return false;
    } else {
        return android.util.Patterns.EMAIL_ADDRESS.matcher(target).matches();
    }
}

public void showAlertValidation() {
    AlertDialog.Builder alertDialog = new AlertDialog.Builder(RegisterActivity.this);
    alertDialog.setTitle("Failed");
    alertDialog.setMessage("Invalid Email");
    alertDialog.setNegativeButton("Close", new DialogInterface.OnClickListener() {
        public void onClick(DialogInterface dialog, int which) {
            dialog.cancel();
        }
    });
    alertDialog.show();
}

And this is my EditText validation code

editTextEmail= (EditText) findViewById(R.id.editTextEmail);
email = editTextEmail.getText().toString();
if(email.length() == 0) {
    editTextEmail.setError("Email required!");
    if (isValidEmail(email)) {
          Toast.makeText(getApplicationContext(),"valid email address",Toast.LENGTH_SHORT).show();
     }
     else{
          showAlertValidation();
     }
}

The problem is the result of the EditText. When the value of EditText is null, it run showAlertValidation(); But if the value of EditText is "email" or "email@example" or "email@example.com", it not run showAlertValidation(); Anything wrong with my code?