How to dynamically create a class and instantiate it in Java?

Question

I'm fairly new to Java and I am coming to it from a C++ background. I am working with a class that has to be extended before it's protected constructor is called. I only need the class in one instance. Is there a way I can dynamically create the class AND instantiate it at the same time?

I found similar posts but not quite hitting the mark. I have the following code as an example but of course it's syntactically incorrect.

final ffd.tokens.CountryTokens cToken = new class USA extends ffd.tokens.CountryTokens
{
    USA (String value)
    {
        super(value);
    }
} ("USA");

This might help: http://stackoverflow.com/questions/8913406/java-inline-class-definition — Jon Egeland, Mar 20 '13 at 21:00

Andrew · Answer 1 · 2013-03-20T22:09:00.253

1

Something like this?

final ffd.tokens.CountryTokens cToken = new ffd.tokens.CountryTokens("someValue")
{
// override something
};

Corrections:

Even with protected methods you can create a Builder that will extend ffd.tokens.CountryTokens (pretty crazy huh?)

public abstract class CountryBuilder extends ffd.tokens.CountryTokens {
   public CountryBuilder () { super("useless-data"); }    
   public abstract ffd.tokens.CountryTokens build (String val); 
}

Using:

CountryBuilder builder = new CountryBuilder (){
   @Override
   public ffd.tokens.CountryTokens build(String val) {
      return new ffd.tokens.CountryTokens(val) {};
   }
};

builder.build("USA");
builder.build("Canada");

I think you get the idea.

edited Mar 20 '13 at 22:09

answered Mar 20 '13 at 21:07

Andrew

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The problem is the CountryTokens counstructor is protected. – jiveturkey Mar 20 '13 at 21:12
That's pretty cool and I keep forgetting about that pattern. But I was just hoping there was a one-liner solution. Thanks for all the great input though. – jiveturkey Mar 21 '13 at 14:06

score 0 · Answer 2 · answered Mar 20 '13 at 21:37

I think I got it. I'm always thinking dynamic allocation with Java but if I simply create a local instance I did it this way.

class USA extends ffd.tokens.CountryTokens
{

    public USA() { super("USA"); }

} USA country;

Now I have my local variable country of type USA.

How to dynamically create a class and instantiate it in Java?

2 Answers2