Java抽象类：受保护的字段或公共集/获取方法

Question

If I got an abstract class that I'm intended on creating sub classes from, is it better practice to have the fields in the abstract class to be protected or have the sub classes use setters and getters instead? Are there any pros and cons?

For instance:

public abstract class MyAbstractClass {
    // option A
    protected int myProtectedInt;

    // option B
    private int myPrivateInt;
    public void setMyPrivateInt() {}
    public int getMyPrivateInt() {}
}

public class MySubClass extends MyAbstractClass {
    // etc
}

Answer 1

Well, it's in part subjective (depends on the scenario) and part preference. I personally never open the fields even to the children classes. Preferring private fields with protected (or public, as needed) getters and setters have helped me a great deal in the past. While it adds a few more characters to code, and makes the code look a little less intuitive, I can list a few pros of my preferred approach that may convince you to start using getters/setters with private fields:

1. Better control: The parent class knows exactly what changed and what was accessed. Instead of a child class (or grand child) directly modifying the fields, they have to use the setters, giving the parent class the visibility that might come handy some day

2. Better flexibility: the parent class has the flexibility to change how the fields are maintained, possibly calculated or even refactores significantly without imoacting any of the children classes as long as the signatures of the getter/setters are preserved.

3. Logging, data access and validations: the getter/setter methods can have programmatic logic to log or check for the data type or perform validations before or after the access or modification. You may be able to add business logic to ensure the caller has access to reading or writing to the fields.

4. Better description: methods can be documented better (JavaDocs of methods can be made much more explanatory than the same of the member variables)

Hope this helps.