如何使用地图创建类对象的副本？

Question

I have a class

public class student 
{
  private int Id;
  private map<String , String> subjects;
  private map<String , String> teachers;
  private String name; 
}

Let me explain the scenario more clearly . I have a function which is taking Student object as a parameter . This function is being called from various other classes . Now in this function I am creating seven threads to perform some computation based on the student input object . Though there is no modification of the student object presently . Still I want to keep it safe by passing in copies of the student object so that if anyone later on modifies the input in any of the threads It should not modify other threads.

So how can i create a new object for the map ? Also another solution I could try is to create this class as immutable but even then the map is a problem . How to make map immutable .

Answer 1

If the threads have to manipulate the object:

• create copies of the objects and maps, for example by using Map<String, String> subjects = new HashMap<>()
• if your objects are becoming more complex use a copy-library (like dozer) or use serialization (like jaxb)

If the threads do not have to manipulate the object:

• just pass the same instance to all threads
• for safety you could make the maps immutable with the methods in the Collections class

By the way:

• consider storing lists of Subject objects and Teacher objects. This makes your code easier to extend, than using maps.