Following this article
Method-1) Following works for android 2.2 onwards
    public final static boolean isValidEmail(CharSequence target) {
    if (target == null) {
        return false;
    } else {
        return android.util.Patterns.EMAIL_ADDRESS.matcher(target).matches();
    }
}
Method-2) Using Regular Expressions and adding the validation to textChangeListener of EditText:
 EdiText emailValidate;
String email = emailValidate.getEditableText().toString().trim();
String emailPattern = "[a-zA-Z0-9._-]+@[a-z]+\\.+[a-z]+";
emailValidate .addTextChangedListener(new TextWatcher() { 
    public void afterTextChanged(Editable s) { 
    if (email.matches(emailPattern) && s.length() > 0)
        { 
            Toast.makeText(getApplicationContext(),"valid email address",Toast.LENGTH_SHORT).show();
            // or
            textView.setText("valid email");
        }
        else
        {
             Toast.makeText(getApplicationContext(),"Invalid email address",Toast.LENGTH_SHORT).show();
            //or
            textView.setText("invalid email");
        }
    } 
    public void beforeTextChanged(CharSequence s, int start, int count, int after) {
    // other stuffs 
    } 
    public void onTextChanged(CharSequence s, int start, int before, int count) {
    // other stuffs 
    } 
}); 
Method-3
    public static boolean isEmailValid(String email) {
    boolean isValid = false;
    String expression = "^[\\w\\.-]+@([\\w\\-]+\\.)+[A-Z]{2,4}$";
    CharSequence inputStr = email;
    Pattern pattern = Pattern.compile(expression, Pattern.CASE_INSENSITIVE);
    Matcher matcher = pattern.matcher(inputStr);
    if (matcher.matches()) {
        isValid = true;
    }
    return isValid;
}
Method-4
if (!emailRegistration.matches("[a-zA-Z0-9._-]+@[a-z]+.[a-z]+")) {
                       edttextEmail.setError("Invalid Email Address");
                   }