Several different classes to extend one, each reusing toString() method from superclass?

[Russell Bateman]

I know this is a pretty beginning Java question and if I knew what to call it, I could simply Google for the answer. If I have a class A that's going to be a "subset" of other classes B, C and probably others...

public class A
{
    protected int x;

    public String toString()
    {
        return x + "";
    }
}

How do I code class B (and C, etc.) such that...

public class B extends A
{
    int y;    // class C will have int z;, etc.

    public String toString()
    {
        StringBuilder sb = new StringBuilder();

        // use A's toString() instead of repeating the code?
        sb.append( y + "" );
        return sb.toString();
    }
}

(Please answer the question in the comment above.)

Profuse thanks for taking pity on an old C programmer still too often struggling with the concepts.

Russ

[Phil English]

Russell Bateman wrote:I know this is a pretty beginning Java question and if I knew what to call it, I could simply Google for the answer. If I have a class A that's going to be a "subset" of other classes B, C and probably others...

public class A
{
    protected int x;

    public String toString()
    {
        return x + "";
    }
}

How do I code class B (and C, etc.) such that...

public class B extends A
{
    int y;    // class C will have int z;, etc.

    public String toString()
    {
        StringBuilder sb = new StringBuilder();

        // use A's toString() instead of repeating the code?
        sb.append( y + "" );
        return sb.toString();
    }
}

(Please answer the question in the comment above.)

Profuse thanks for taking pity on an old C programmer still too often struggling with the concepts.

Russ

How about declaring a int printMe variable in the super class. Then each subclass can set whatever value to printMe and resuse the super method?

Note - assuming you want to preserve x and not overwrite that.

[Russell Bateman]

After cracking Eckel's Thinking in Java, I am reminded that all I was looking for was

    public String toString()  
    {  
        StringBuilder sb = new StringBuilder();  
  
        // use A's toString() instead of repeating the code?  It's simple, do this:
        sb.append( super.toString() );
        sb.append( y + "" );  
        return sb.toString();  
    }

Sorry about wasting everyone's time.

Thanks.

[Rob Spoor]

Russell Bateman wrote:

        sb.append( y + "" );  

Don't do that. just use sb.append(y). You probably have that + "" to convert y into a String. However, by appending it to the StringBuilder you're already doing that (in a more efficient way).

[Russell Bateman]

(Sorry right, in my actual code, I'm not doing that. Thanks.)

[Darryl Burke]

There's the pattern adopted in the JDK Component class hierarchy; java.awt.Component's toString() method looks like this:

    public String toString() {
        return getClass().getName() + "[" + paramString() + "]";
    }

Subclasses override a protected String paramString() method that returns information relevant to the specific class, sometimes calling into the super implementation and appending to it.

[Rajdeep Biswas]

Darryl Burke wrote:There's the pattern adopted in the JDK Component class hierarchy; java.awt.Component's toString() method looks like this:

    public String toString() {
        return getClass().getName() + "[" + paramString() + "]";
    }

Subclasses override a protected String paramString() method that returns information relevant to the specific class, sometimes calling into the super implementation and appending to it.

This is a very good implementation, although you can always SB the Strings.