如何将值从一个Java类复制到具有相同属性的另一个类

Question

Here is my class structure: (with omitted getters and setters)

public class A { 
    public List<QuestionTemplate> qTemplateList;
}

public class QuestionTemplate {
    public List<QuestionList> qList;
}

public class QuestionList {
    public String questionText;
    public String questionChoice;
}

----------------------------------------------------

public class B { 
    public List<QuestionTemplate> qTemplateList;
}

public class QuestionTemplate {
    public List<QuestionList> qList;
}

public class QuestionList {
    public String questionText;
    public String questionChoice;
} 

I would like to copy the data from class B to class A by hand, manually copy fields instead of using any type of mapper.

I tried walking the lists and tried to copy from one list to the other (starting with the most inner list but ran into tons of issues. Please forgive as I am new to this. I tried. Please help.

Answer 1

Please refer this Copy all values from fields in one class to another through reflection

Similar problem is already answered there.

Answer 2

This code requires Java 7 or later.

Option A Copy the data manually by iterating through:

    A a = new A();

    ..

    List<QuestionTemplate> templateListCopy = new LinkedList<>();
    for (QuestionTemplate template : a.qTemplateList) {
        List<QuestionList> questionListCopy = new LinkedList<>();
        for (QuestionList question : template.qList) {
            QuestionList questionCopy = new QuestionList();
            questionCopy.questionText = question.questionText;
            questionCopy.questionChoice = question.questionChoice;
            questionListCopy.add(questionCopy);
        }
        QuestionTemplate questionTemplateCopy = new QuestionTemplate();
        questionTemplateCopy.qList = questionListCopy;
        templateListCopy.add(questionTemplateCopy);
    }
    B b = new B();
    b.qTemplateList = templateListCopy;

Option B Modify the classes and add copy methods to make the implementation code much less confusing:

class A {
    public List<QuestionTemplate> qTemplateList;

    public A copy() {
        A copy = new A();
        List<QuestionTemplate> questionTemplateListCopy = new ArrayList<>(qTemplateList.size());
        for (QuestionTemplate questionTemplate : qTemplateList) {
            questionTemplateListCopy.add(questionTemplate.copy());
        }
        copy.qTemplateList = questionTemplateListCopy;
        return copy;
    }
}

class QuestionTemplate {
    public List<QuestionList> qList;

    public QuestionTemplate copy() {
        QuestionTemplate copy = new QuestionTemplate();
        List<QuestionList> qListCopy = new ArrayList<>(qList.size());
        for (QuestionList questionList : qList) {
            qListCopy.add(questionList.copy());
        }
        copy.qList = qListCopy;
        return copy;
    }
}

class QuestionList {
    public String questionText;
    public String questionChoice;

    public QuestionList copy() {
        QuestionList copy = new QuestionList();
        copy.questionText = questionText;
        copy.questionChoice = questionChoice;
        return copy;
    }
}

Implementation:

A a = new A();

..

B b = new B();
b.qTemplateList = a.copy().qTemplateList;