Java 17 Recipes

5-2. Making Private Fields Accessible to Other 
Classes
 Problem
You want to create private instance members so that outside classes cannot access 
them directly. However, you would also like to make those private members accessible 
in a controlled manner.
 Solution
Encapsulate the private fields by making getters and setters to access them. The 
following code demonstrates the declaration of a private field, followed by accessor 
(getter) and mutator (setter) methods that obtain or set the value of that field from an 
outside class.
Chapter 5 ObjeCt-Oriented java

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153
private String firstName;
/**
* @return the firstName
*/
public String getFirstName() {
return firstName;
}
/**
* @param firstName the firstName to set
*/
public void setFirstName(String firstName) {
this.firstName = firstName;
}
The getFirstName() method can be used by an outside class to obtain the value 
of the firstName field. Likewise, an outside class can use the setFirstName(String 
firstName) method to set the value of the firstName field.
 How It Works
Often when fields are marked as private within a class, they still need to be made 
accessible to outside classes to set or retrieve their value. Why not just work with the 
fields directly and make them public then? It is not good programming practice to 
work directly with fields of other classes because access can be granted in a controlled 
fashion by using accessors (getters) and mutators (setters). By not coding directly against 
members of another class, you also help decouple the code, which helps to ensure that 
if an object changes, others that depend on it are not adversely affected. As you can see 
from the example in the solution to this recipe, hiding fields and working with public 
methods to access those fields is fairly easy. Simply create two methods; one to obtain 
the value of the private field, the getter or accessor method. And the other to set the 
value of the private field, the setter or mutator method. In the solution to this recipe, 
the getter returns the unaltered value contained within the private field. Similarly, the 
setter sets the value of the private field by accepting an argument of the same data type 
as the private field and then setting the value of the private field to the value of the 
argument.
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154
The class using the getters or setters for access to the fields does not know any 
details behind the methods. For instance, a getter or setter method could contain more 
functionality if required. Furthermore, the details of these methods can be changed 
without altering any code that accesses them.
Note Using getters and setters does not completely decouple code. in fact, many 
people argue that using getters and setters is not a good programming practice. 
Objects that use the accessor methods still need to know the type of instance field 
they are working against. that said, getters and setters are standard techniques 
for providing external access to private instance fields of an object. to make the 
use of accessor methods in a more object-oriented manner, declare them within 
interfaces and code against the interface rather than the object itself.