Scala class extends Java class

I'm a little new to this, so sorry if it may seem a naive question. Let's say I have Java class as follows:

public class A {
      private final regex = "folder1/folder2/folder3/.*";
      private Pattern pattern;
      
      A(...) {
       this.pattern = Pattern.Compile(regex)
      }


      public func1(String str){
        if (...){
          Matcher m = pattern.matcher(str)
        }  
      }
}

now I'm trying to extend the class A with scala so I can override the regex field and therefore the pattern field following with it.

class B(...) extends A(...){
}

But I'm not sure how to override the regex to be regex = "folder4/.*" for class B

You could pass it into a protected constructor:

class A {
    private final String regex;

    protected A(String regex) {
        this.regex = regex;
    }

    public A() {
        this("folder1/folder2/folder3/.*");
    }
}

class B extends A {
    public B() {
        super("folder4/.*");
    }
}

Or just declare each as a constant and use an overrideable method to read them:

class A {
    private static final String REGEX = "folder1/folder2/folder3/.*";
    
    protected String getRegex() {
        return REGEX;
    }
}

class B {
    private static final String REGEX = "folder4/.*";
    
    @Override
    protected String getRegex() {
        return REGEX;
    }
}