不变类中的对象作为成员变量 [英] Objects in an immutable class as member variable

问题描述

我有一个X类，其中包含Employee对象.我想使X类不可变.现在，即使我将Employee对象声明为final，Employee类也独立存在，并且人们可以访问该特定employee对象的setter方法.可以有一个普通的Employee类，另一个拥有Employee的不可变类X，但是一旦分配了Employee，我们就不能更改它的值?

I have a class X which holds Employee object. I want to make the class X as immutable. Now even if I declare the Employee object as final the Employee class exists independently and people can access the setter methods of that particular employee object. Is it possible to have a normal class Employee and another immutable class X which holds Employee but we cannot change value of Employee once it is assigned?

public final class X {

private final Employee emp;

public X (Employee e){
   this.emp = e;

}
public Employee getEmp(){

return emp;

}

} 

我不想使它成为不可变的雇员类别，只想使X类成为不可变的.因此，一旦分配了雇员，就不应对其进行更改. 在不使Employee类不变的情况下可行吗? 我希望让Employee类独立存在，所以不想私有化其构造.

The employee class I dont want to make it immutable, just want to make the class X as immutable.Hence once an employee is assigned it should not be allowed to change it. Is that possible without making the class Employee as immutable. I want class Employee to exist independently so do not want to privatize its construction.

推荐答案

您不必公开不可变类的Employee成员.您可以引入仅公开Employee相关字段的getter方法.

You don't have to expose the Employee member of the immutable class. You can introduce getter methods that would expose only relevant fields of the Employee.

public final class X {

  private final Employee emp;

  public X (Employee e){
     this.emp = e.clone ();
  }

  public String getEmpName(){
    return emp.getName();
  }

  public int getEmpSalary(){
    return emp.getSalary();
  }

} 

当然，您还有另一件事要做，以确保该类确实是不可变的.构造函数应创建传递给它的Employee的副本.否则，构造函数的调用者仍然可以引用Employee，并且可以更改该对象.

Of course, there's one more thing you have to do to ensure the class is really immutable. The constructor should create a copy of the Employee passed to it. Otherwise, the caller of the constructor would still have a reference to the Employee, and would be able to change that object.

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