How to use anonymous classes in java

[sony vijay]

Hi,

I am trying to perform some rule checking in my application. I am using an inner interface(Check) within a class and am creating anonymous classes of the type interface(Check). Using this approach, the idea is to create an anonymous class for each rule. Please see code below:

public class Rules {       
    public interface Check {
        public boolean check(String input);
    }
    static Check REG_EXP = new Check() {
        @Override
        public boolean check(String input) {
            // To DO: Check if the given input is a regular expression
            return false;
        }
    };
    static Check IS_NUMBER = new Check() {
        @Override
        public boolean check(String input) {
            //To Do: Check whether the given input is a string representation of a number
            return false;
        }
    };
}

But, I am not sure how to call the methods of anonymous classes from another class? Say, there's another class called TypeCheck. How do I call the IS_NUMBER.check method?

public class TypeCheck {
    public TypeCheck() {
        String a = "1";
        // How to call the method to check whether the variable 'a' is a number i.e call IS_NUMBER.check(a)
        // boolean isvalid = ??????
    }
}

I have never used interfaces with anonymous classes before and I am trying this out. Thank YOU!

[Rob Spoor]

Just like any class that implements Check, you can simply use a Check reference and call the method(s) from Check:

public class TypeCheck {   
    public TypeCheck() {   
        String a = "1";   
        Check check = Rules.IS_NUMBER;
        if (check.check(a)) {
            System.out.println(a + " is valid");
        }
    }   
}

[Campbell Ritchie]

And the Check instances should probably be marked final.

How are you going to check whether a String is a regular expression? That seems impossible to me.

[sony vijay]

@Campbell Ritchie: I would use the the java regex Patterns to check whether a string is a regular expression:

import java.util.regex.Pattern;
import java.util.regex.PatternSyntaxException;

I would do a Patter.compile(input) within a try-catch block. The catch block would throw a PatternSyntaxException. I hope you get the general idea. Please let me know if you need more explanation. But, I am not sure whether the the java Pattern of regular expressions matches the javascript regular expression patterns. I am yet to check on that.

[Campbell Ritchie]

I see what you mean, but you can only check for syntax errors, not what the regular expression will test for.

[sony vijay]

Thanks! That was a useful link. But, I am trying to just check the syntax errors for now. Any idea if there are any differences between Java and Javascript regular expressions?

[Campbell Ritchie]

They are bound to be different. Start looking here.