java: can't use constructors in abstract class

Question

Hi.

I created the following abstract class for job scheduler in red5:

package com.demogames.jobs;

import com.demogames.demofacebook.MysqlDb;
import org.red5.server.api.IClient;
import org.red5.server.api.IConnection;
import org.red5.server.api.IScope;
import org.red5.server.api.scheduling.IScheduledJob;
import org.red5.server.api.so.ISharedObject;
import org.apache.log4j.Logger;
import org.red5.server.api.Red5;

/**
 *
 * @author ufk
 */
abstract public class DemoJob implements IScheduledJob {

protected IConnection conn;
protected IClient client;
protected ISharedObject so;
protected IScope scope;
protected MysqlDb mysqldb;

protected static org.apache.log4j.Logger log = Logger
    .getLogger(DemoJob.class);

protected DemoJob (ISharedObject so, MysqlDb mysqldb){

       this.conn=Red5.getConnectionLocal();
       this.client = conn.getClient();
       this.so=so;
       this.mysqldb=mysqldb;
       this.scope=conn.getScope();
 }

 protected DemoJob(ISharedObject so) {
   this.conn=Red5.getConnectionLocal();
   this.client=this.conn.getClient();
   this.so=so;
   this.scope=conn.getScope();
 }

 protected DemoJob() {
   this.conn=Red5.getConnectionLocal();
   this.client=this.conn.getClient();
   this.scope=conn.getScope();
 }

}

Then i created a simple class that extends the previous one:

public class StartChallengeJob extends DemoJob {

 public void execute(ISchedulingService service) {

   log.error("test");

 }

}

The problem is that my main application can only see the constructor without any parameters. with means i can do new StartChallengeJob() why doesn't the main application sees all the constructors ?

thanks!

Answer 1

For the StartChallengeJob class shown in your question, the compiler generates a default constructor, which implicitly calls the default constructor of the base class.

If this default behaviour is not what you want, you need to explicitly define one or more constructor(s) in StartChallengeJob, which then call the desired base class constructor. E.g. if you want both a default and a parameterized constructor, you need to define both:

public class StartChallengeJob extends DemoJob {

 public StartChallengeJob(){
       // implicitly calls the base class default constructor: super();
 }

 public StartChallengeJob (ISharedObject so, MysqlDb mysqldb){
       super(so, mysqldb);
 }

 public void execute(ISchedulingService service) {

   log.error("test");

 }

}

Answer 2

Constructors aren't inherited. StartChallengeJob effectively looks like this:

public class StartChallengeJob extends DemoJob {

  public StartChallengeJob() {
    super();
  }

  public void execute(ISchedulingService service) {    
    log.error("test");   
  }    
}

If you want all of the superclass constructor signatures to be available, you'll need to have those constructors in StartChallengeJob too:

public class StartChallengeJob extends DemoJob {

  public DemoJob (ISharedObject so, MysqlDb mysqldb) {
    super(so, mysqldb);
  }

  public DemoJob (ISharedObject so) {
    super(so);
  }

  public StartChallengeJob() {
    super();
  }

  public void execute(ISchedulingService service) {    
    log.error("test");   
  }    
}