通过声明新方法来继承Java抽象类

Question

In my android project I have an abstract class Request

package Managers;

import java.util.HashMap;

public abstract class Request {
    public interface Completion {
        void execute(HashMap<String, Object> result);
    }

    protected Completion completion;
    protected HashMap<String, Object> requestResult;

    public void setCompletion(Completion newCompletion) {
        completion = newCompletion;
        if (requestResult != null) {
            completion.execute(requestResult);
            requestResult = null;
        }
    }
}

And in my RequestsManager Class I have instantiated it like so

public static Request numberAvailabilityCheck = new Request() {
    public String isSuccess = "isSuccess";
    public String result = "result";

    public void sendRequest(String number) {
        new java.util.Timer().schedule(new java.util.TimerTask() {
            @Override
            public void run() {
                requestResult = new HashMap<String, Object>();
                requestResult.put(isSuccess, true);
                requestResult.put(result, true);
                if (completion != null) {
                    completion.execute(requestResult);
                    requestResult = null;
                }
            }
        }, 5000);
    };
};

In my MainFragment class I need to use numberAvailabilityCheck like so

private View.OnClickListener checkEventListener = new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        RequestsManager.numberAvailabilityCheck.setCompletion(numberAvailabilityCheckCompletion);
        ViewRelatedUtils.closeKeyboard(getActivity());
        isProcessingCheckNumber = true;
        showProcessing();
        RequestsManager.numberAvailabilityCheck.sendRequest(numberField.getText());
    }
};

But compiler does not see RequestsManager.numberAvailabilityCheck.sendRequest method in MainFragment. Why compiler doesn't see it? What understands compiler when I declare public method sendRequest in RequestsManager like so? And how can I make a compiler see it?

Answer 1

Note that your code can invoke the method setCompletion() without a problem!

That method is defined on you base class. The other method is only defined within the scope of your anonymous inner class instantiation! Therefore the compiler doesn't "see" it and prevents you from invoking it!

Please note: if you could somehow turn that field into a local variable declared without a type (by using the new var keyword of Java 10), your code would work: as the compiler can infere the fact that you added that method. But by declaring that object to be of type Request, the compiler can only tell you that this method does not exist.

But using var is not a good approach, instead the solution could be: add an abstract method for sendRequest() to your class Request! If that isn't possible, then consider to not use a single abstract base class, why not have additional abstract classes that extend your base class, each one providing a slightly different send method.

Answer 2

Thanks to all for describing me why compiler doesn't see a method. I have found a solution that, I think, is the most comfort solution for me. In RequestsManager I have declared a public class NumberAvailabilityCheck that extends Request and public static member of that class numberAvailabilityCheck.

public static class NumberAvailabilityCheck extends Request {
    public String isSuccess = "isSuccess";
    public String result = "result";

    public void sendRequest(String number) {
        new java.util.Timer().schedule(new java.util.TimerTask() {
            @Override
            public void run() {
                requestResult = new HashMap<String, Object>();
                requestResult.put(isSuccess, true);
                requestResult.put(result, true);
                if (completion != null) {
                    completion.execute(requestResult);
                    requestResult = null;
                }
            }
        }, 5000);
    };
};
public static NumberAvailabilityCheck numberAvailabilityCheck = new NumberAvailabilityCheck();

Note that NumberAvailabilityCheck cannot be declared as private.