抽象类多重继承

Question

I have following structure of classes:

• abstract class A
• class B extends class A
• abstract class C extends class B
• class D extends class C

I have a static method which has a return type A and returns B - this is ok. I want to change this method, so it still has return type A , but it returns D - this causes problems:

java.lang.Error: Unresolved compilation problem: 
    D cannot be resolved to a type

Why is this happening? They should have the same interface as the parent classes don't they? Edit:

This is the method im trying to modify

public static CodeFormatter createDefaultCodeFormatter(Map<String, ?> options) {
        if (options == null)
            options = CCorePlugin.getOptions();
        return new CCodeFormatter(options);
    }

It is a class from the CDT Project ( http://git.eclipse.org/c/cdt/org.eclipse.cdt.git/commit/?id=a83be9db5b41c0a593425798a2af91060588b38a ). Instead of CCodeFormatter I am trying to return MyFormatter. Class CCodeFormatter ( our B in example ) extends CodeFormatter ( our A in example ) and is extended by abstract class MyFormatter ( or C in example ) and this class is extended by class MyFormatter ( D in example ). So I add its project to required bundles (in MANIFEST.MF) and then I import it and return new MyFormatter(options). In the end, this error happens.

public static CodeFormatter createDefaultCodeFormatter(Map<String, ?> options) {
        if (options == null)
            options = CCorePlugin.getOptions();
        return new MyFormatter(options);
    }

the "D" class

public class MyFormatter extends MyAbstractFormatter{

    @Override
    protected CodeFormatterVisitor getFormatterVisitor(DefaultCodeFormatterOptions preferences, int offset, int length) {
        return new MyFormatterVisitor(preferences, offset, length);
    }

}

and "C" class

public abstract class MyAbstractFormatter extends CCodeFormatter {

    public MyAbstractFormatter() {
        super();
    }

    public MyAbstractFormatter(DefaultCodeFormatterOptions preferences) {
        super(preferences);
    }

    public MyAbstractFormatter(DefaultCodeFormatterOptions defaultCodeFormatterOptions, Map<String, ?> options) {
        super(defaultCodeFormatterOptions, options);
    }

    public MyAbstractFormatter(Map<String, ?> options) {
        super(options);
    }

    @Override
    public void setOptions(Map<String, ?> options) {
        super.setOptions(options);
    }

    @Override
    public TextEdit format(int kind, String source, int offset, int length, int indentationLevel, String lineSeparator) {
        return super.format(kind, source, offset, length, indentationLevel, lineSeparator);
    }

}

Answer 1

Ok, problems seems to be in cyclic dependency (and not in abstract classes). My project is dependent on CDT project and I am trying to add my project to this project's required bundles, I am making this CDT project dependent on my project. (Altought Eclipse usually detects this problem, this is probably not the case).