Answers to Self-Check Problems - Building Java Programs: A Back to Basics Approach - page 1070

17. The keyword this refers to the object on which a method or constructor has been
called (sometimes called the “implicit parameter”). It is used to access or set the
object's field values, to call the object's methods, or to call one constructor from
another.
18. // Constructs a Point object with the same x and y
// coordinates as the given Point.
public Point(Point p) {
this.x = p.x;
this.y = p.y;
}
Here is an alternative version:
// Constructs a Point object with the same x and y
// coordinates as the given Point.
public Point(Point p) {
this(p.x, p.y); // call the (int, int) constructor
}
19. Abstraction is the ability to focus on a problem at a high level without worrying
about the minor details. Objects provide abstraction by giving us more powerful
pieces of data that have sophisticated behavior without having to manage and
manipulate the data directly.
20. Items declared public may be seen and used from any class. Items declared
private may be seen and used only from within their own classes. Objects' fields
should be declared private to provide encapsulation, so that external code can't
make unwanted direct modifications to the fields' values.
21. To access private fields, create accessor methods that return their values. For
example, add a getName method to access the name field of an object.
22. // Sets this Point's x coordinate to the given value.
public void setX(int newX) {
x = newX;
}
// Sets this Point's y coordinate to the given value.
public void setY(int newY) {
y = newY;
}