javascalaclassoverridingextending

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


Solution

  • 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;
        }
    }