Android Validation rules

Validation.java

public static boolean isValidEmail(String target) {
	boolean check1 = Patterns.EMAIL_ADDRESS.matcher(target).matches();
	Pattern pattern;
	Matcher matcher;
	String EMAIL_PATTERN = "^[_A-Za-z0-9-]+(\\.[_A-Za-z0-9-]+)*@[A-Za-z0-9]+(\\.[A-Za-z0-9]+)*(\\.[A-Za-z]{2,})$";
	pattern = Pattern.compile(EMAIL_PATTERN);
	matcher = pattern.matcher(target);
	boolean check2 = matcher.matches();
	return target.isEmpty() || check1 && check2;
}

public static boolean isValidPhone(String target) {
	return target.startsWith("09") && target.trim().length() == 11 && target.matches("[0-9]+");
}

public static boolean isValidPassword(String target) {
	return target.length() >= 8 && ASCII.isASCII(target) && target.matches("\\A\\p{ASCII}*\\z");
}

public static boolean isValidName(String target) {
	return Pattern.compile("^(?=.*[a-zA-Z가-힣])[a-zA-Z가-힣]{1,}$").matcher(target).matches();
}

public static boolean isValidNickName(String target) {
	return Pattern.compile("^(?=.*[a-zA-Z\\d])[a-zA-Z0-9가-힣]{2,12}$|^[가-힣]$").matcher(target).matches();
}

public static boolean isNumber(String target) {
	return Pattern.compile("^(-?0|-?[1-9]\\d*)(\\.\\d+)?(E\\d+)?$").matcher(target).matches();
}