Answer:
What must a subclass do to modify a private superclass instance variable?
a) The subclass must simply use the name of the superclass instance variable.
b) The subclass must declare its own instance variable with the same name as the superclass instance variable.
c) The subclass must use a public method of the superclass (if it exists) to update the superclass's private instance variable.
d) The subclass must have its own public method to update the superclass's private instance variable.
Option c) The subclass must use a public method of the superclass (if it exists) to update the superclass's private instance variable is the correct answer.
Private instance variables of a superclass are not directly accessible by subclasses. However, if the superclass provides a public method to modify the variable, the subclass can use this method to indirectly modify the private instance variable.
For example, consider the following superclass with a private instance variable and a public method to modify it:
public class Superclass {
private int value;
public void setValue(int newValue) {
this.value = newValue;
}
}
If a subclass wants to modify the value of the private instance variable value, it can do so by calling the public method setValue() of the superclass:
public class Subclass extends Superclass {
public void updateValue(int newValue) {
setValue(newValue); //call to public method of superclass to update private instance variable
}
}
In this example, the updateValue() method of the subclass uses the public setValue() method of the superclass to modify the private instance variable value.
Step-by-step explanation: