Multiple inheritance design issue in Java

Question

How do you deal with having only single inheritance in java? Here is my specific problem:

I have three (simplified) classes:

public abstract class A         


        

Answer 1

The problem is not "how to deal with single inheritance". What you're missing is not really a design pattern but learning to design the API separately from the implementation.

I would implement it like so:

public interface WordDescriptor {
    void getKind();
    Word getWord();
}

public interface Word {
    String getWord();
}

public class SimpleWord implements Word {
    private String word;

    public SimpleWord(String word) { this.word = word; }
    public String getWord() { return word; }
}

public class SimpleWordDescriptor implements WordDescriptor {
    private Word word;
    private String kind;

    public SimpleWordDescriptor(Word word, String kind) {
        this.word = word;
        this.kind = kind; // even better if WordDescriptor can figure it out internally
    }

    public Word getWord() { return word; }

    public String getKind() { return kind; }
}

With this basic setup, when you want to introduce a length property, all you have to do is this:

public interface LengthDescriptor {
    int getLength();
}

public class BetterWordDescriptor extends SimpleWordDescriptor
                                  implements LengthDescriptor {
    public BetterWordDescriptor(Word word, String kind) {
        super(word, kind);
    }

    public int getLength() { getWord().length(); }        
}

The other answers that uses composition of properties as well as the Decorator pattern are also entirely valid solutions to your problem. You just need to identify what your objects are and how "composable" they are, and how they are to be used - hence designing the API first.