类java中的ArrayList获取器和设置器

Question

public class Employee                                               
{
private String name;
private String department;


private ArrayList<Employee>job= new ArrayList();

// just want to add getter and setter for this ArrayList

public void setJob(Employee j)
{
job.add(j);

// this is my setter

I want to be able to add later on as many 'job' as I want by extending the arraylist

Answer 1

While you can have setters and getter of List type, you should think carefully about their implementation, because most lists are mutable. For instance, assume that you want to validate that the jobs list is not empty.

public void setJob(List<Employee> jobs) {
  if (jobs.isEmpty()) throw new RuntimeException();
  this.job = jobs;
}

Now the following code produces an employee without jobs:

Employee e = ...;
e.setJobs(jobs);
jobs.clear();
//the employee now has no jobs :-(

You can avoid this issue by making a defensive copy

public void setJob(List<Employee> j) {
  this.job = new ArrayList<>(j);
}

The same applies to the getter. If you implement it as:

public List<Employee> getJobs() {
   return this.jobs;
}

you are allowing the caller to modify the private job list without invoking the corresponding setter: myEmployee.getJobs().clear() .

In this case, you may return an unmodifiable list instead of returning the inner object.

public List<Employee> getJobs() {
   return java.util.Collections.unmodifiableList(this.jobs);
}    

Answer 2

通常对于集合或数组，您将使用addJob，removeJob和getJobs而不是获取/设置对。