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Newsgroups: comp.lang.java.programmer
Date: Tue, 29 Jan 2019 10:11:52 -0800 (PST)
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Subject: How to make my library independent using DI
From: mike <mikaelpetterson@hotmail.com>
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Xref: csiph.com comp.lang.java.programmer:38719

Hi,

I am creating a library that can be used with different java applications.
Sometimes I need data from different applications but I want to avoid a direct dependency to these applications.

In my library I have the following classes:

package scrap;


public interface MyDataClass {
    String productNumber();
    String version();
    String time();


}

and 

public class MyDataClassImpl implements MyDataClass{
    
    private ExternalDataService externalDataService;
    
    public MyDataClassImpl(ExternalDataService externalDataService){
        this.externalDataService = externalDataService;
    }

    @Override
    public String productNumber() {
      //Here we have a dependency to an external library call it x
       return externalDataService.productNumber();
    }

    @Override
    public String version() {
        //Here we have a dependency to an external library call it x
       return externalDataService.version();
    }

    @Override
    public String time() {        
      return calcTime();
    }
    
    
    private String calcTime () {
        return "";
        
    }
}

as well as:

package scrap;


public interface ExternalDataService {
    
    public String productNumber();
    
    public String version();

}


Then in the application using this lib I have:

package other;

import scrap.ExternalDataService;

public class AHelper implements ExternalDataService{

    @Override
    public String productNumber() {
        return methodA();
    }

    @Override
    public String version() {
        return methodB();
    }
    
    
    public String methodA() {
        return "";
    }
    
    String methodB() {
        return "";
    }
}

I have two questions:

1. How can I inject AHelper into MyDataClassImpl without creating a "hard dependency" without using a DI container?
2. If I used a container like Guice how would that look like? 

All hints welcome.

br,

Mike