Question

In a specific scenario here,

I have a manger called UserManger used to handle CRUD for user

This manager is “Singleton” and correct by design.

But in update method I have logic

public User update (User u) 
{

    // This line is problematic?
    User u1 = new User();

    copy(u,u1);
    //Some logic
    dao.update(u);

}

Will creating any new objects in singleton manager problematic? Especially for a very concurrent system.

Will

public User update (User u, User u1)
{

    copy(u,u1);
    //Some logic
    dao.update(u);
}

Solve my problem?

Answer 1

Just creating an object within a singleton method won’t cause any problems. You’re not sharing any state between threads, after all.

You would have potential problems if you had state within the singleton itself – but all you’ve shown is creating a local variable, not changing an instance variable. Each invocation of a method has its own entirely separate set of local variables. Two threads can both be executing the same method, but they won’t see each other’s local variables.