merging one object into another object [duplicate]

Question

I have two Objects of same type.I want to create a method which can merge the properties of two object and can return a single object.

For Example: Consider a class ABC having 4 fields

Class ABC{
String name;
String id;
String salary;
String status;
}

Suppose the first object is

ABC[name=ZEE,id=2,salary=null,status=1]

and the second object is

ABC[name=john,id=null,salary=12200,status=null]

I want to make a generic method which can merge these two objects and can give result output as:

ABC[name=ZEE,id=2,salary=12200,status=1]

The method Should take two parameters of Object type:

Object  mergeObject(Object Obj1, Object Obj2){
}

Note: It will take the first object property if both the objects have non-null value for that property.

Answer 1

You're going to have to go the reflection route. I'm assuming you have a default constructor, otherwise the following won't work. Also, it needs two same types. It won't copy inherited fields, for that, you also need to add some code from here.

@SuppressWarnings("unchecked")
public static <T> T mergeObjects(T first, T second) throws IllegalAccessException, InstantiationException {
    Class<?> clazz = first.getClass();
    Field[] fields = clazz.getDeclaredFields();
    Object returnValue = clazz.newInstance();
    for (Field field : fields) {
        field.setAccessible(true);
        Object value1 = field.get(first);
        Object value2 = field.get(second);
        Object value = (value1 != null) ? value1 : value2;
        field.set(returnValue, value);
    }
    return (T) returnValue;
}

Here's an example

public static class ABC {
    private int id;
    private String name;
    private int[] numbers;

    public ABC() {
    }


    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int[] getNumbers() {
        return numbers;
    }

    public void setNumbers(int[] numbers) {
        this.numbers = numbers;
    }
}

public static void main(String[] args) throws InstantiationException, IllegalAccessException {
    ABC abc = new ABC();
    abc.setId(1);
    abc.setName("Hello");
    int[] newnumbers = new int[5];
    for(int i = 0; i < newnumbers.length; i++) {
        newnumbers[i] = i;
    }
    abc.setNumbers(newnumbers);
    ABC abc2 = new ABC();
    abc2.setName("World");

    ABC abcFinal = mergeObjects(abc, abc2);
    System.out.println("Properties of ABC Final:");
    System.out.println("ID: " + abcFinal.getId());
    System.out.println("Name: " + abcFinal.getName());
    System.out.println("Numbers: " + Arrays.toString(abcFinal.getNumbers()));
}

Output:

Properties of ABC Final:
ID: 1
Name: Hello
Numbers: [0, 1, 2, 3, 4]

Answer 2

In case you want to create a new Object use:

public ABC mergeABC(ABC obj1, ABC obj2){
    ABC retVal = new ABC();
    retVal.name   = ((obj1.name   != null) ? obj1.name   : obj2.name   );
    retVal.id     = ((obj1.id     != null) ? obj1.id     : obj2.id     );
    retVal.salary = ((obj1.salary != null) ? obj1.salary : obj2.salary );
    retVal.status = ((obj1.status != null) ? obj1.status : obj2.status );
    return retVal;
}

If you want to "reuse" obj1 or obj2, simply use this as return value.