Extending Classes and Inheritance - Beginning Java - page 320

The getFirst() and getNext() methods are intended to be used together to access all the objects stored
in the list. The getFirst() method returns the object stored in the first ListItem object in the list and
sets the current data member to refer to the first ListItem object. After calling the getFirst() method,
successive calls to the getNext() method return subsequent objects stored in the list. The method updates
current to refer to the next ListItem object, each time it is called. When the end of the list is reached,
getNext() returns null .

TRY IT OUT: Using the General Linked List
You can now define the PolyLine class so that it uses a LinkedList object. All you need to do is put
a LinkedList variable as a class member that you initialize in the class constructors, and implement all
the other methods you had in the previous version of the class to use the LinkedList object:

public class PolyLine {
// Construct a polyline from an array of coordinate pairs
public PolyLine(double[][] coords) {
Point[] points = new Point[coords.length]; // Array to hold

points

// Create points from the coordinates
for(int i = 0; i < coords.length ; ++i) {
points[i] = new Point(coords[i][0], coords[i][1]);

}

// Create the polyline from the array of points
polyline = new LinkedList(points);

}

// Construct a polyline from an array of points
public PolyLine(Point[] points) {
polyline = new LinkedList(points); // Create the

polyline
}

// Add a Point object to the list
public void addPoint(Point point) {
polyline.addItem(point); // Add the point to

the list
}

// Add a point from a coordinate pair to the list
public void addPoint(double x, double y) {
polyline.addItem(new Point(x, y)); // Add the point to

the list
}

// String representation of a polyline