Object-Oriented Concepts - SCJP Sun Certified Programmer for Java Platform SE6 - page 398

The computeArea method in InvalidShape has the default access, a weaker access than
protected . The following compiler error is generated:
InvalidShape.java:7: computeArea() in InvalidShape cannot override
computeArea() in Shape; attempting to assign weaker access privileges;
was protected
double computeArea() {
^
1 error
The computeArea method in InvalidShape can only have public or protected access.
Private and Abstract Methods
An abstract method cannot be declared private because a private method is not visible
in a child class and therefore cannot be overridden. For example, the following code does
not compile:
public abstract class Shape {
private abstract double computeArea();
}
The following compiler error is generated:
Shape.java:2: illegal combination of modifiers: abstract and private
private abstract double computeArea();
^
1 error
As you can see, the compiler states that abstract and private are not a valid
combination of modifi ers.
The abstract modifi er is only applied to classes and methods. Constructors cannot be
overridden, so it does not make sense for a constructor to be abstract. For example, the
following Square class does not compile:
public abstract class Square {
private int side;
public abstract Square(int s) {
side = s;
}
}