Extend java.lang.String

Question

java.lang.String is declared as final, however are there any mechanisms available legitimate or otherwise to extend it and replace the equals(String other) method?

Answer 1

Now, there is a way. With manifold it's possible to extend every Java Class. Here is an example for String:

package extensions.java.lang.String;

import manifold.ext.api.*;

@Extension
public class MyStringExtension {

  public static void print(@This String thiz) {
    System.out.println(thiz);
  }

  @Extension
  public static String lineSeparator() {
    return System.lineSeparator();
  }
}

Can than be used as follow:

String name = "Manifold";
name.print();
String.lineSeparator();

Another example can be found here: https://jaxenter.com/manifold-code-generator-part-2-151762.html

Notice, that manifold is still alpha.

Answer 2

It is not possible to directly inherit String class as it is final. Also wrapper classes java.lang.Integer, java.lang.Float, etc... are final.

Answer 3

No, absolutely not. If you want some "other" kind of string, create another type which might contain a string:

public final class OtherString {
    private final String underlyingString;

    public OtherString(String underlyingString) {
        this.underlyingString = underlyingString;
    }        

    // Override equals however you want here
}

Answer 4

You cannot extend a class that is marked as final. You can use composition to either put a String object inside or you can hand roll your own version. This can be accomplished via character arrays and the other magic that goes into creating String classes.

Answer 5

I guess the closest you can come is making some class that implements CharSequence. Most JDK string manipulation methods accept a CharSequence. StringBuilder for example. Combined with a good implementation of toString(), the various methods of String and valueOf(), you can come pretty close to a natural substitute.