catch exception if boolean is false - exception

Question

This is the easiest example of a complex issue. I haven't found the example of this problem anywhere in the entire internet. I'm validating the input in a validationMethod that return Boolean. Now, I need to use this method in calling class (run the flow if return is true, catch exception if return is false).
public class StringUtil{
public static boolean validateNumInput(String UserInput)
{
if(UserInput.matches("[0-9]+")){
return true;
} return false;
}
}
public class Main{
public static void main(String[] args){
String a="012*+";
try{
if(StringUtil.validateNumInput(a)){
System.out.println(StringUtil.validateNumInput(a));
}
}catch(Exception e){
System.out.println("Big problem");
}
}
}

Answer 1

According to the documentation, you can filter catch clauses with a Boolean predicate. So, your validation method would need to throw an exception which you could filter for in your catch clause. But if you're doing that, you might as well roll your own custom exception and not have to deal with the Boolean at all. The other alternative is, in your calling code, treat the return code as a return code and throw your own exception.
Option 1:
public class StringUtil{
public static boolean validateNumInput(String UserInput)
{
if(UserInput.matches("[0-9]+")){
return true;
}
throw new Exception ("Validation failed!");
}
}
public class Main{
public static void main(String[] args){
String a="012*+";
try{
if(StringUtil.validateNumInput(a)){
System.out.println(StringUtil.validateNumInput(a));
}
}catch(Exception e) when (e.Message == "Validation failed!") {
System.out.println("Big problem");
}
}
}
Option 2:
public class Main{
public static void main(String[] args){
String a="012*+";
try{
if(StringUtil.validateNumInput(a)){
System.out.println(StringUtil.validateNumInput(a));
} else {
throw new Exception ();
}
}catch(Exception e) {
System.out.println("Big problem");
}
}
}