Getters and Setters

We add getters and setters to the superclass to allow subclasses to access private superclass fields.

public class Employee2 extends Person {
  private String title;
  private double salary;
  // ...
  public String getTitle() {
    return title;
  }
  public void setTitle(String title) {
    this.title = title;
  }
  public double getSalary() {
    return salary;
  }
  public void setSalary(double salary) {
    this.salary = salary;
  }
}

The subclass can now call the inherited getter or setter method to access or change the superclass field.

public class DataAnalyst2 extends Employee2 {
  private String securityClearance;
  // ...

  public String getInformation() {
    return firstName + " " + lastName + " " + age  // protected in Person
        + " " + getTitle() + " " + getSalary()     // visible methods from Employee
        + " " + securityClearance;                 // private in DataAnalyst
  }
}

Validation in Setters

Setters may use validation or data manipulation to ensure that data is acceptable or formatted correctly.

Below, the setter for hour ensures the field is not greater than 12.

public class Clock {
  private int hour;
  private int seconds;
  private long nanoseconds;
  private String amOrPm;

  public void setHour(int h) {
    if (h > 12) {
      h = h - 12;
    }
    hour = h;
  }

  // ...
}

Methods are Inherited, Not Copied

The compiler does not copy superclass methods into the subclass. * The methods exist only in the superclass. * Since the methods are part of the superclass, but callable from the subclass, the subclass can access the superclass's private data.

Practice Exercise

When we instantiate a subclass, only one object is created in memory.

The new object contains memory allocations for all of the fields in the subclass, as well as those in the superclass - even the private fields it can't access.

You will not have a separate object created for the subclass and the superclass.

In the Eclipse debugger, we can see that DataAnalyst has the Employee fields, even though it can't access them directly.

Note: even though the private superclass fields exist in memory for the object, they are not inherited by the subclass, because the subclass cannot access them directly.

Drill

Inheritance/com.example.inheritance.drills.Employee * Add getters and setters to the Employee class.

Inheritance/com.example.inheritance.drills.DataAnalyst

(If you did not finish DataAnalyst, use the class from the ...solutions package) * Fix DataAnalyst to use the Employee getters in its getInfo() method to output salary and title. * Add a six-arg constructor that uses setters to assign each of the fields in Person, Employee, and DataAnalyst. * Remove the one-arg DataAnalyst constructor. * Create a DataAnalyst in EmployeeApp and output its information. (Solution: Employee4.java, DataAnalyst2.java, EmployeeApp3.java)

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