Demo :: No-IF

factory.java

public static RegisterRule newInstance(String validatorRule) {
    if ("NameEmptyRule".equals(validatorRule)) {
        return new NameEmptyRule();
    } else if ("NameFormatRule".equals(validatorRule)) {
        return new NameFormatRule();
    } else if ("EmailEmptyRule".equals(validatorRule)) {
        return new EmailEmptyRule();
    }
    return null;
}

factory2.java

public static RegisterRule newInstance(String validatorRuleClass){
    return (RegisterRule) Class.forName(validatorRuleClass).newInstance();
}

factory3.java

static Map<String , RegisterRule> ruleMapper = new HashMap<String, RegisterRule>() {
    {
        put("NameEmptyRule", new NameEmptyRule());
        put("NameFormatRule", new NameFormatRule());
        put("EmailEmptyRule", new EmailEmptyRule());
    }
};

public static RegisterRule newInstance(String validatorRule) {
    return ruleMapper.get(validatorRule);
}

factory4.java

enum RegisterType {
    NameEmptyRule {
        public RegisterRule create() {
            return new NameEmptyRule();
        }
    },
    NameFormatRule {
        public RegisterRule create() {
            return new NameFormatRule();
        }
    },
    EmailEmptyRule {
        public RegisterRule create() {
            return new EmailEmptyRule();
        }
    };
    public RegisterRule create() {
        return null;
    }
}

public static RegisterRule newInstance(RegisterType registerType) {
    return registerType.create();
}

test.java

@Test
public void validInput() {
    User user = new User();
    user.setName("Somkiat");
    user.setEmail("[email protected]");
    user.setAge(30);
    
    RuleFactory.newInstance("demo.validate.refactor.NameEmptyRule").validate(user);
}