How to swap objects in Java?
Let’s say we have a class called “Car” with some attributes. And we create two objects of Car, say car1 and car2, how to exchange the data of car1 and car2?
A Simple Solution is to swap members. For example, if the class Car has only one integer attribute say “no” (car number), we can swap cars by simply swapping the members of two cars.
c1.no = 2 c2.no = 1
What if we don’t know members of Car?
The above solution worked as we knew that there is one member “no” in Car. What if we don’t know members of Car or the member list is too big. This is a very common situation as a class that uses some other class may not access members of other class. Does below solution work?
no = 1, model = 101 no = 2, model = 202
As we can see from above output, the objects are not swapped. We have discussed in a previous post that parameters are passed by value in Java. So when we pass c1 and c2 to swap(), the function swap() creates a copy of these references.
Solution is to use Wrapper Class If we create a wrapper class that contains references of Car, we can swap cars by swapping references of wrapper class.
no = 2, model = 202 no = 1, model = 101
So a wrapper class solution works even if the user class doesn’t have access to members of the class whose objects are to be swapped.
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