Validating an input string against some enum fields

Question

I have this enum below:

public enum TestEnum {
 h1, h2, h3, h4;
 public static String forCode(int code) {
 return (code >= 0 && code < values().length) ? values()[code].name() : null;
 }
 public static void main(String[] args) {
 System.out.println(TestEnum.h1.name());
 String ss = "h3";
 try {
 TestEnum.valueOf(ss); // but this validates with all the enum values
 System.out.println("valid");
 } catch (IllegalArgumentException e) {
 System.out.println("invalid");
 } 
 }
}

I need to check if the enum value represented by my string ss is one of my enum values h1, h2 or h4. So if h3 is being passed as a string, I would like to return false or throw IllegalArgumentException. I won't need to validate ss with h3 in the enum.

I came up with the below code to do this with the enum, but I believe there is a more elegant solution.

public enum TestEnum {
 h1, h2, h3, h4;
 public static boolean checkExcept(String el, TestEnum... except){
 boolean results = false;
 try{
 results = !Arrays.asList(except).contains(TestEnum.valueOf(el));
 }catch (Exception e){}
 return results;
 }
 public static String forCode(int code) {
 return (code >= 0 && code < values().length) ? values()[code].name() : null;
 }
 public static void main(String[] args) {
 String ss = "h3";
 if(TestEnum.checkExcept(ss,TestEnum.h1, TestEnum.h2, TestEnum.h3)){
 System.out.println("valid");
 }else{
 System.out.println("invalid");
 }
 }
}

Is there any better way of solving this problem?

Answer 1

I would pass a TestEnum instead of a String to your method, forcing the exception handling to be outside the method. I don't see why you are using Strings at all actually (although I suspect that this is only a small part of your code, and that you have your reasons for needing this).

I would do some refactoring and use EnumSet, which could make your code something like this: (untested code, but I believe it should work)

public static void main(String[] args) {
 String enumName = "h3";
 EnumSet<TestEnum> except = EnumSet.of(TestEnum.h1, TestEnum.h2, TestEnum.h3);
 boolean valid;
 try {
 valid = !except.contains(TestEnum.valueOf(enumName));
 } catch (IllegalArgumentException e) { valid = false; }
 System.out.println(valid ? "valid" : "invalid");
}

Note that I have gotten rid of your entire method here as I think that when you use EnumSet like this, you don't need the method. But of course you can put the relevant parts of the above code into a method.

• david: What about if the String enumName is h10? It should return false as well? Correct? But it is throwing exception with your current code.
• Simon Forsberg: @user2809564 As if that's a big problem to solve.... ;) See edit.
• Simon Forsberg: @ringbearer If you pass enumName = "h4" in this case it is a valid enum and will not throw, but contains will return false.
• ring bearer: Right, i assumed before noting that OP wanted a filter.

Answer 2

You can create an isValid or checkValid method inside the enum and override it in h3 if it's not changing runtime.

public enum TestEnum {
 h1, 
 h2, 
 h3 {
 @Override
 public boolean isValid() {
 return false;
 }
 },
 h4;
 public boolean isValid() {
 return true;
 }
}

It returns true for h1, h2 and h4, false for h3.

You could eliminate the results variable from checkExcept:

public static boolean checkExcept(String el, TestEnum... except) {
 try {
 return !Arrays.asList(except).contains(TestEnum.valueOf(el));
 } catch (Exception e) {
 return false;
 }
}

Please note that catching Exception is almost always a bad idea. I'd catch a more specific exception here (IllegalArgumentException).

• Simon Forsberg: Overriding the isValid method is not a flexible solution for different validation requirements. I agree with catching IllegalArgumentException though.

Answer 3

Catching exception or its sub type is bad idea. This should do it more proper way as mentioned code below.

public static boolean contains(String test) {
 for (EnumType type : EnumType.values()) {
 if (type.name().equals(test)) {
 return true;
 }
 }
 return false;
}

• Simon Forsberg: This is generally a good option, but in this case it doesn't solve the same problem. The question asks for I need to check if the enum value represented by my string ss is one of my enum values h1, h2 or h4. So if h3 is being passed as a string, I would like to return false or throw IllegalArgumentException.