Java：对象成员如何从父类调用方法？

Question

maybe that isn't possible, but currently I'm not sure about it.

Take a look at simple example:

public class Job {
  private Document jobDoc;

  public JOB() {
    // some code to determine the job to process
    this.jobDoc = job_to_process;
  }

  public boolean readJob() {
    // do some validation stuff and read properties from Job
    String myproperty = this.job.getProperty("jobtype");

    // Here I need your advise
    // How to call a method from the parent class??
    parent.setjobtype(myproperty); // <= parent is just for Demonstration!
  }
}

public class Application {
  private Job myjob = null;
  private String jobtype = "";

  public Application() {
    this.myjob = new Job();
    // read the job to fill the application type
    myjob.readJob(); // <= this method should call setjobtype from this class!!
  }

  public void setjobtype(String type) {
   this.jobtype = type;
  }
}

From what I know I could change the readJob like readJob(Application appl). But then you are able to build circulars.

Any tipps are welcome!

Kindly regards Frank

Answer 1

As per you example the Job class dont have a super class other than Object. But if it did had a parent class with setjobtype method you could directly invoke it. eg:

class ParentJob {
    String jobType;
    public void setjobtype(String jobType){
        this.jobType = jobType;
    }
}

class Job extends ParentJob{
  private Document jobDoc;

  public Job() {
    // some code to determine the job to process
    this.jobDoc = job_to_process;
  }

  public boolean readJob() {
    // do some validation stuff and read properties from Job
    String myproperty = this.job.getProperty("jobtype");

    setjobtype(myproperty); // This will call parent method
  }
}

In your case Application is not the parent class. In order to invoke the setjobtype of application you need to create an instance of application class in readJob method and then invoke it. Or in order to set proper values to current object you need to pass an instance of it to readJob method and then invoke the setjobtype method like

class Job{
  private Document jobDoc;

  public Job() {
    // some code to determine the job to process
    this.jobDoc = job_to_process;
  }

  public boolean readJob(Application app) {
    // do some validation stuff and read properties from Job
    String myproperty = this.job.getProperty("jobtype");

    // Here I need your advise
    // How to call a method from the parent class??
    app.setjobtype(myproperty); // <= parent is just for Demonstration!
  }
}

public class Application {
  private Job myjob = null;
  private String jobtype = "";

  public Application() {
    this.myjob = new Job();
    // read the job to fill the application type
    myjob.readJob(this); // <= this method should call setjobtype from this class!!
  }

  public void setjobtype(String type) {
   this.jobtype = type;
  }
}

Answer 2

To call a method from parent class. Simply write that method as it is because child class contains all method of parent classes.

Other situation is if you have overridden that method in child class then you can use super.method()

But condition important in the both cases is you have proper access modifier for the function. It must not be private.

Answer 3

To call the setJobType() method of the Application class, you need a reference to an object of this class in the readJob() method.

public boolean readJob(Application application) {
    // do some validation stuff and read properties from Job
    String myproperty = this.job.getProperty("jobtype");

    // Here I need your advise
    // How to call a method from the parent class??
    application.setjobtype(myproperty); // <= parent is just for Demonstration!
}

And you can call readJob() passing the reference to the application:

public Application() {
    this.myjob = new Job();
    // read the job to fill the application type
    myjob.readJob(this); // Passing the reference to the Application object
}

This solves your problem, but I would suggest to change the design as the setObjectType() method seems to be more appropriate in the Job class .

Answer 4

Thanks guys! To anhance the method readJob was clear. But as I said in the inital post. If you doing it this way you can build a Loop!

It is not possible to call a method from the parent!

Greetz Frank