Generic for construct a class

[avseq anthoy]

Dear all
I have a Class as below

public class PrintLog
{
    public void printBillingLog( List<Billing> billingList , String action )
    {
        for ( int i = 0 ; i < billingList.size() ; i++ )
        {
            Billing billing = billingList.get( i );
            BillingLog log = new BillingLog( billing );
            log.setAction( action );
            log.setId( i );
            System.out.println( log );
        }
    }

    public void printOrderLog( List<Order> orderList , String action )
    {
        for ( int i = 0 ; i < orderList.size() ; i++ )
        {
            Order order = orderList.get( i );
            OrderLog log = new OrderLog( order );
            log.setAction( action );
            log.setId( i );
            System.out.println( log );
        }
    }
    
}

I think the logic of printBillingLog and printOrderLog function are similar.
So I want to use a generic way to reduce the function code.
I think the code as below , but I had got stock.

public class NewPrintLog< T >
{
    public void printLog( List<T> list )
    {
        for ( int i = 0 ; i < list.size() ; i++ )
        {
            T entity = list.get( i );
            ...
            ...
            ...
            System.out.println( log );
        }
    }
}

Now I don't know how to create OrderLog( the constructor's paramter is Order ) and BillingLog( the constuctor's paramter is Billing) in generic way. And how to call the setAction() method in each xxxLog entity.
Can somebody teach me how to solve the problem?
Billing、BillingLog、Order、OrderLog class as below

public class Billing
{
    private String id;
    private String billingName;
    private String billingDetail;

    public String getBillingName()
    {
        return billingName;
    }

    public void setBillingName( String billingName )
    {
        this.billingName = billingName;
    }

    public String getId()
    {
        return id;
    }

    public void setId( String id )
    {
        this.id = id;
    }

    public String getBillingDetail()
    {
        return billingDetail;
    }

    public void setBillingDetail( String billingDetail )
    {
        this.billingDetail = billingDetail;
    }
}

public class BillingLog
{
    private int id;
    private String billingName;
    private String billingDetail;
    private String action;

    public BillingLog( Billing billing )
    {
        this.billingName = billing.getBillingName();
        this.billingDetail = billing.getBillingDetail();
    }

    public int getId()
    {
        return id;
    }

    public void setId( int id )
    {
        this.id = id;
    }

    public String getBillingName()
    {
        return billingName;
    }

    public void setBillingName( String billingName )
    {
        billingName = billingName;
    }

    public String getAction()
    {
        return action;
    }

    public void setAction( String action )
    {
        this.action = action;
    }

    public String getBillingDetail()
    {
        return billingDetail;
    }

    public void setBillingDetail( String billingDetail )
    {
        this.billingDetail = billingDetail;
    }

    @Override
    public String toString()
    {
        StringBuffer sb = new StringBuffer();
        sb.append( "id:" )
        .append( id )
        .append( ",billingName:" + billingName )
        .append( ",billingDetail:" + billingDetail )
        .append( ",action:" + action );
        
        return sb.toString();
    }

}

public class Order
{
    private int id;
    private String orderName;
    private int orderPrice;

    public int getId()
    {
        return id;
    }

    public void setId( int id )
    {
        this.id = id;
    }

    public String getOrderName()
    {
        return orderName;
    }

    public void setOrderName( String orderName )
    {
        this.orderName = orderName;
    }

    public int getOrderPrice()
    {
        return orderPrice;
    }

    public void setOrderPrice( int orderPrice )
    {
        this.orderPrice = orderPrice;
    }

}

public class OrderLog
{
    private int id;
    private String orderName;
    private int orderPrice;
    private String action;

    public OrderLog()
    {}

    public OrderLog( Order order )
    {
        this.orderName = order.getOrderName();
        this.orderPrice = order.getOrderPrice();
    }

    public int getId()
    {
        return id;
    }

    public void setId( int id )
    {
        this.id = id;
    }

    public String getOrderName()
    {
        return orderName;
    }

    public void setOrderName( String orderName )
    {
        this.orderName = orderName;
    }

    public String getAction()
    {
        return action;
    }

    public void setAction( String action )
    {
        this.action = action;
    }

    public int getOrderPrice()
    {
        return orderPrice;
    }

    public void setOrderPrice( int orderPrice )
    {
        this.orderPrice = orderPrice;
    }

    @Override
    public String toString()
    {
        StringBuffer sb = new StringBuffer();
        sb.append( "id:" + id )
        .append( ",orderName:" + orderName )
        .append( ",orderPrice:" + orderPrice )
        .append( ",action:" + action );
        
        return sb.toString();
    }
    
    

}

[Manish Singh]

Make a 'Log' interface.
Get you logger classes Order and Billing Log implement Log interface

[avseq anthoy]

Manish Singh wrote:Make a 'Log' interface.
Get you logger classes Order and Billing Log implement Log interface

Thanks for your reply.
I think the meaning as below

public interface ILog
{
    public void setId( int id );
    
    public void setAction( String action );
}

But the original way that conctruct BillingLog and OrderLog as below.

OrderLog log = new OrderLog(order);
BillingLog log = new BillingLog(billing);

I still didn't know how to construct the BillingLog and OrderLog in generic way.
Can somebody teach me how to solve it ?
Thanks

public class NewPrintLog< T , Log extends ILog>
{
    public void printLog( List<T> list )
    {
        for ( int i = 0 ; i < list.size() ; i++ )
        {
            T entity = list.get( i );
            // OrderLog log = new OrderLog(order);
            Log log = null; // how to constructor BillingLog or OrderLog ?
            log.setAction( "create" );
            log.setId( i );
            System.out.println( log );
        }
    }
}

[Rob Spoor]

You'll need an additional interface:

public interface LogFactory<T, Log extends ILog>
{
    public Log createLog(T entity);
}

You'll then get implementing classes BillingLogFactory implements LogFactory<Billing, BillingLog> and OrderLogFactory implements LogFactory<Order, OrderLog>. The NewPrintLog class then changes somewhat:

public class NewPrintLog<T , Log extends ILog>   
{   
    public void printLog(List<T> list, LogFactory<T, Log> factory) // additional parameter
    {   
        for ( int i = 0 ; i < list.size() ; i++ )   
        {   
            T entity = list.get(i);   
            Log log = factory.createLog(entity);
            log.setAction("create");   
            log.setId(i);   
            System.out.println(log);   
        }   
    }   
} 

For a little more performance you can make singletons out of your factories:

public class BillingLogFactory implements LogFactory<Billing, BillingLog>
{
    private static final BillingLogFactory INSTANCE = new BillingLogFactory();

    private BillingLogFactory() {}

    public static BillingLogFactory getInstance()
    {
        return INSTANCE;
    }

    public BillingLog createLog(Billing billing)
    {
        return new BillingLog(billing);
    }
}

You can then simply pass BillingLogFactory.getInstance() to your printLog method.

[David Newton]

ILog should be re-named Loggable...