package effectivejava.creatinganddestoyingobjects;

import java.io.FileInputStream;
import java.io.IOException;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Map;
import java.util.Properties;

/**
* Consider providing static factory methods instead of constructors
*
* Create properties file - Item1.properties with the following entries:
* Item1Impl1=effectivejava.creatinganddestoyingobjects.Item1Impl1
* Item1Impl2=effectivejava.creatinganddestoyingobjects.Item1Impl2
*
*/
public abstract class Item1 {

    // Maps String key to corresponding Class object
    private static Map implementations = null;

    private static synchronized void initMapIfNecessary() {
        if( implementations == null ) {
            implementations = new HashMap();

            // Load implementation class names and keys from
            // Properties file, translate names into Class
            // objects using Class.forName and store mappings.
            // ...
            Properties prop = new Properties();
            try {
                prop.load( new FileInputStream( "effectivejava/creatinganddestoyingobjects/Item1.properties" ));
            } catch (IOException e) {
                System.out.println( e );
            }

            for (Enumeration e = prop.propertyNames(); e.hasMoreElements();) {
                Object obj = e.nextElement();
                try {
                    implementations.put( obj , Class.forName( prop.getProperty( (String) obj ) ) );
                } catch (ClassNotFoundException cnfe) {
                    System.out.println( cnfe );
                }
            }

            prop = null;
        }
    }

    public static Item1 getInstance( String key ) {
        initMapIfNecessary();
        Class c = (Class) implementations.get( key );
        if( c == null ) {
            return new DefaultItem1();
        }

        try {
            return (Item1) c.newInstance();
        } catch (Exception e) {
            return new DefaultItem1();
        }
    }

    public abstract void printClassName();

    public static void main( String args[] ) {
        Item1.getInstance("").printClassName();
        Item1.getInstance("Item1Impl1").printClassName();
        Item1.getInstance("Item1Impl2").printClassName();
    }
}
 

class DefaultItem1 extends Item1 {

    public void printClassName() {
        System.out.println( "Item1" );
    }

}
 

class Item1Impl1 extends Item1 {

    public void printClassName() {
        System.out.println( "Item1Impl1" );
    }
}

class Item1Impl2 extends Item1 {
    public void printClassName() {
        System.out.println( "Item1Impl2" );
    }
}