Generic Data Extraction from different classes

Question

I have the following problem and wonder whether there is an efficient solution to it. (I am using Java)

Imagine you have multiple different types of classes holding the same data in variables with different name and consider this given.

Here an example: Imagine there are the three empiric values as member within a container class

short color
int size
String shape

and consider the two classes

class1
class2

class1 has three member variables being the empiric values:

short rgb_color -> corresponds to color
long bigness -> corresponds to bigness
String contour -> corresponds to shape

class2 has three member variables being the empiric values:

int cmyk -> corresponds to color
int greatness -> corresponds to bigness
String shapecountour -> corresponds to shape

As you see the names are different. So if I want to import the values from class one and two into the container class, I would need to convert every parameter by itself in order to add it to the container class and thus I need to type as there are member variables (here 6) e.g. see this pseudo code for the import function:

public void import(class1 class){
   this.color = (short) class.rgb_color;
   this.size = (int) class.bigness;
   this.shape = (String) class.contour;
}
public void import(class2 class){
   this.color = (short) class.cmyk;
   this.size = (int) class.greatness;
   this.shape = (String) class.shapecontour;
}

Now imagine problems, where there are much more parameters. Is there a generic way to solve the import as to do it one by one for each member?

Thank you for your help.

EDIT: Thanks already for the fast answers. As I said I cannot modify class1 and class2.

I have checked the reflection, where they have this example for changing the fields.

public class Book {
    public long chapters = 0;
    public String[] characters = { "Alice", "White Rabbit" };
    public Tweedle twin = Tweedle.DEE;

    public static void main(String... args) {
    Book book = new Book();
    String fmt = "%6S:  %-12s = %s%n";

    try {
        Class<?> c = book.getClass();

        Field chap = c.getDeclaredField("chapters");
        out.format(fmt, "before", "chapters", book.chapters);
        chap.setLong(book, 12);
        out.format(fmt, "after", "chapters", chap.getLong(book));

        Field chars = c.getDeclaredField("characters");
        out.format(fmt, "before", "characters",
               Arrays.asList(book.characters));
        String[] newChars = { "Queen", "King" };
        chars.set(book, newChars);
        out.format(fmt, "after", "characters",
               Arrays.asList(book.characters));

        Field t = c.getDeclaredField("twin");
        out.format(fmt, "before", "twin", book.twin);
        t.set(book, Tweedle.DUM);
        out.format(fmt, "after", "twin", t.get(book));

        // production code should handle these exceptions more gracefully
    } catch (NoSuchFieldException x) {
        x.printStackTrace();
    } catch (IllegalAccessException x) {
        x.printStackTrace();
    }
    }
}

But still I need to call each variable by name as e.g. "chapters". What do I get wrong?

score 0 · Answer 1 · answered Aug 17 '12 at 12:38

0

You can use java reflection api to obtain list of available fields and than match them by type.

answered Aug 17 '12 at 12:38

Kojotak

2,020
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score 0 · Answer 2 · answered Aug 17 '12 at 12:43

Why don't you do this change your design a bit : Create a parent class and pull those parameters in to parent class, and let your Class1,Class2 extend new Parent class. Now access those parameters.

class BaseClass{
    short color;
    int size;
    String shape;
}

class  Class1 extends BaseClass{
-----Other Class Properties----------   
}

class Class2 extends BaseClass{
-----Other Class Properties----------   
}

score 0 · Accepted Answer · edited May 23 '17 at 11:48

You have two options to resolve the issue:

To change the design, as suggested above. It seems that inheritance of some base class (with these three fields) should work fine.
If you don't have a way to modify these two classes (class1, class2) => You have to specify the mapping between the fields anyway. The straightforward way is your option with converters. Other option is to define the mapping with annotations/xml/etc. and to use some mapping tool. These conversation has a good list of them:

any tool for java object to object mapping?

Dozer seems to be the most promising for me.

Generic Data Extraction from different classes

3 Answers3