#508 Some reflections can not be used

[xiaolibang]

Hi Eric,

In the developing of android, I got a section of code blew
public class ResponseData
{
private DataObject dataObject;

public static class DataObject  
{  
    private long time;  
}

}
I tried to create an instance of DataObject with DataObject.class.newInstance(), but failed after obfuscation.
I debugged that and found there is no constructors for DataObject class in the byte code file.

I saw the instruction for ProGuard v4.7, and found the unused parameterless constructors will be removed after obfuscation/optimization.

I have to modified the code like
public class ResponseData
{
private DataObject dataObject = new DataObject();

public static class DataObject  
{  
    private long time;  
}

}
It worked well.

So the type of reflection can not be used even if the DataObject class is configured to be kept . The empty constructor is useful in reflection sometimes. Could the empty constructor be kept after obfuscation/optimization?

Best regards
xiaolibang

[Eric Lafortune]

Thanks for your report. This case seems to work fine for me, with ProGuard 4.11, but also with the older ProGuard 4.7. For instance:

public class Test {

  public static void main(String[] args) {
    try {
      Inner.class.newInstance();
    } catch (Exception e) {
      e.printStackTrace();
    }
  }

  public static class Inner {}
}

Can you provide such an example?

If necessary, you can always keep all empty constructors with

-keepclassmembers class * {
    <init>();
}

[xiaolibang]

Thanks for you reply.
The code which can not work is like:
public class ResponseData {
private DataObject dataObject;

public static class DataObject {
    private long lightOnTime;
}

public static void main(String[] args) {
    try {
        Class<?> dataClazz = ResponseData.class.getDeclaredField("dataObject").getType();
        dataClazz.newInstance();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

}

But it can work well if empty constructors are kept with
-keepclassmembers class * {
<init>();
}