Overloading constructors

[Dirk Neefs]

Hi,
I have a problem when invoking overloaded constructors when I pass null as a parameter. This is my code:

 public class RawValue
{
int key;
String value;
    public RawValue(
        int key,
        String value )
    {
        this.key = key;
        this.value = value;
    }
    public RawValue(
        int key,
        byte[] value )
    {
        this.key = key;
        this.value = value;
    }
    public RawValue(
        int key,
        char[] value )
    {
        this.key = key;
        this.value = value;
    }
    
    public boolean isString(  )
    {
        return ( value instanceof String );
    }
}[ 

When I call isString() it returns false.
My question now is: what are the rules to invoke an overloaded constructor and what is the impact on this for the null value?
[ May 22, 2003: Message edited by: Cindy Glass ]

[Joel McNary]

Hi, Dirk, and Welcome to JavaRanch.
In general, answer to your question lies in the fact that null is considered to be a very specific value, and when faced with overloaded methods, the most specific one will be called.
(My examples below are methods, but I believe that the same holds true for constructors)
That is, if you had:

public void aMethod(Object anObject){
    System.out.println("Object");
}
public void aMethod(Number aNumber){
    System.out.println("Number");
}
public void aMethod(Integer anInteger){
    System.out.println("Integer");
}

and called aMethod(null), it would print "Integer" since that is the most specific method. However, if you also had

public void aMethod(String aString){
    System.out.println("String");
}

and called aMethod(null), you would get a compile-time error, since the compiler cannot tell what you class you mean for null to be (Integer and String are of equal specific-ness). You would have to cast your null, i.e., aMethod((String)null).
However, when I try to compile you code, I get the following errors:

C:\user\java\sources\RawValue.java:33: incompatible types
found   : byte[]
required: java.lang.String
        this.value = value;
                     ^
C:\user\java\sources\RawValue.java:44: incompatible types
found   : char[]
required: java.lang.String
        this.value = value;
                     ^
2 errors

Of course this is because byte[] and char[] are not Strings in Java.
[ May 22, 2003: Message edited by: Joel McNary ]