chapter07.java

// A simple class hierarchy.

// A class for two-dimensional objects.
class TwoDShape {
  double width;
  double height;

  void showDim() {
    System.out.println("Width and height are " +
                       width + " and " + height);
  }
}

// A subclass of TwoDShape for triangles.
class Triangle extends TwoDShape {
  String style;

  double area() {
    return width * height / 2;
  }

  void showStyle() {
    System.out.println("Triangle is " + style);
  }
}

class Shapes {
  public static void main(String[] args) {
    Triangle t1 = new Triangle();
    Triangle t2 = new Triangle();

    t1.width = 4.0;
    t1.height = 4.0;
    t1.style = "filled";

    t2.width = 8.0;
    t2.height = 12.0;
    t2.style = "outlined";

    System.out.println("Info for t1: ");
    t1.showStyle();
    t1.showDim();
    System.out.println("Area is " + t1.area());

    System.out.println();

    System.out.println("Info for t2: ");
    t2.showStyle();
    t2.showDim();
    System.out.println("Area is " + t2.area());
  }
}

// -----------------------------------------

// A subclass of TwoDShape for rectangles.
class Rectangle extends TwoDShape {
  boolean isSquare() {
    if(width == height) return true;
    return false;
  }

  double area() {
    return width * height;
  }
}

// -----------------------------------------

// Private members of a superclass are not accessible by a subclass.

// This example will not compile.

// A class for two-dimensional objects.
class TwoDShape {
  private double width; // these are
  private double height; // now private

  void showDim() {
    System.out.println("Width and height are " +
                       width + " and " + height);
  }
}

// A subclass of TwoDShape for triangles.
class Triangle extends TwoDShape {
  String style;

  double area() {
    return width * height / 2; // Error! can't access
  }

  void showStyle() {
    System.out.println("Triangle is " + style);
  }
}

// -----------------------------------------

// Use accessor methods to set and get private members.

// A class for two-dimensional objects.
class TwoDShape {
  private double width; // these are
  private double height; // now private

  // Accessor methods for width and height.
  double getWidth() { return width; }
  double getHeight() { return height; }
  void setWidth(double w) { width = w; }
  void setHeight(double h) { height = h; }

void showDim() {
  System.out.println("Width and height are " +
                     width + " and " + height);
  }
}

// A subclass of TwoDShape for triangles.
class Triangle extends TwoDShape {
  String style;

  double area() {
    return getWidth() * getHeight() / 2;
  }

  void showStyle() {
    System.out.println("Triangle is " + style);
  }
}

class Shapes2 {
  public static void main(String[] args) {
    Triangle t1 = new Triangle();
    Triangle t2 = new Triangle();

    t1.setWidth(4.0);
    t1.setHeight(4.0);
    t1.style = "filled";

    t2.setWidth(8.0);
    t2.setHeight(12.0);
    t2.style = "outlined";

    System.out.println("Info for t1: ");
    t1.showStyle();
    t1.showDim();
    System.out.println("Area is " + t1.area());

    System.out.println();

    System.out.println("Info for t2: ");
    t2.showStyle();
    t2.showDim();
    System.out.println("Area is " + t2.area());
  }
}

// -----------------------------------------

// Add a constructor to Triangle.

// A class for two-dimensional objects.
class TwoDShape {
  private double width; // these are
  private double height; // now private

  // Accessor methods for width and height.
  double getWidth() { return width; }
  double getHeight() { return height; }
  void setWidth(double w) { width = w; }
  void setHeight(double h) { height = h; }

  void showDim() {
    System.out.println("Width and height are " +
                       width + " and " + height);
  }
}

// A subclass of TwoDShape for triangles.
class Triangle extends TwoDShape {
  private String style;

  // Constructor
  Triangle(String s, double w, double h) {
    setWidth(w);
    setHeight(h);

    style = s;
  }

  double area() {
    return getWidth() * getHeight() / 2;
  }

  void showStyle() {
    System.out.println("Triangle is " + style);
  }
}

class Shapes3 {
  public static void main(String[] args) {
    Triangle t1 = new Triangle("filled", 4.0, 4.0);
    Triangle t2 = new Triangle("outlined", 8.0, 12.0);

    System.out.println("Info for t1: ");
    t1.showStyle();
    t1.showDim();
    System.out.println("Area is " + t1.area());

    System.out.println();

    System.out.println("Info for t2: ");
    t2.showStyle();
    t2.showDim();
    System.out.println("Area is " + t2.area());
  }
}

// -----------------------------------------

// Add constructors to TwoDShape.
class TwoDShape {
  private double width;
  private double height;

  // Parameterized constructor.
  TwoDShape(double w, double h) {
    width = w;
    height = h;
  }

  // Accessor methods for width and height.
  double getWidth() { return width; }
  double getHeight() { return height; }
  void setWidth(double w) { width = w; }
  void setHeight(double h) { height = h; }

  void showDim() {
    System.out.println("Width and height are " +
                       width + " and " + height);
  }
}

// A subclass of TwoDShape for triangles.
class Triangle extends TwoDShape {
  private String style;

  Triangle(String s, double w, double h) {
    super(w, h); // call superclass constructor

    style = s;
  }

  double area() {
    return getWidth() * getHeight() / 2;
  }

  void showStyle() {
    System.out.println("Triangle is " + style);
  }
}

class Shapes4 {
  public static void main(String[] args) {
    Triangle t1 = new Triangle("filled", 4.0, 4.0);
    Triangle t2 = new Triangle("outlined", 8.0, 12.0);

    System.out.println("Info for t1: ");
    t1.showStyle();
    t1.showDim();
    System.out.println("Area is " + t1.area());

    System.out.println();

    System.out.println("Info for t2: ");
    t2.showStyle();
    t2.showDim();
    System.out.println("Area is " + t2.area());
  }
}

// -----------------------------------------

// Add more constructors to TwoDShape.
class TwoDShape {
  private double width;
  private double height;

  // A default constructor.
  TwoDShape() {
    width = height = 0.0;
  }

  // Parameterized constructor.
  TwoDShape(double w, double h) {
    width = w;
    height = h;
  }

  // Construct object with equal width and height.
  TwoDShape(double x) {
    width = height = x;
  }

  // Accessor methods for width and height.
  double getWidth() { return width; }
  double getHeight() { return height; }
  void setWidth(double w) { width = w; }
  void setHeight(double h) { height = h; }

  void showDim() {
    System.out.println("Width and height are " +
                       width + " and " + height);
  }
}

// A subclass of TwoDShape for triangles.
class Triangle extends TwoDShape {
  private String style;

  // A default constructor.
  Triangle() {
    super();
    style = "none";
  }

  // Constructor
  Triangle(String s, double w, double h) {
    super(w, h); // call superclass constructor

    style = s;
  }

  // One argument constructor.
  Triangle(double x) {
    super(x); // call superclass constructor

    // default style to filled
    style = "filled";
  }

  double area() {
    return getWidth() * getHeight() / 2;
  }

  void showStyle() {
    System.out.println("Triangle is " + style);
  }
}

class Shapes5 {
  public static void main(String[] args) {
    Triangle t1 = new Triangle();
    Triangle t2 = new Triangle("outlined", 8.0, 12.0);
    Triangle t3 = new Triangle(4.0);

    t1 = t2;

    System.out.println("Info for t1: ");
    t1.showStyle();
    t1.showDim();
    System.out.println("Area is " + t1.area());

    System.out.println();

    System.out.println("Info for t2: ");
    t2.showStyle();
    t2.showDim();
    System.out.println("Area is " + t2.area());

    System.out.println();

    System.out.println("Info for t3: ");
    t3.showStyle();
    t3.showDim();
    System.out.println("Area is " + t3.area());

    System.out.println();
  }
}

// -----------------------------------------

// Using super to overcome name hiding.
class A {
  int i;
}

// Create a subclass by extending class A.
class B extends A {
  int i; // this i hides the i in A

  B(int a, int b) {
    super.i = a; // i in A
    i = b; // i in B
  }

  void show() {
    System.out.println("i in superclass: " + super.i);
    System.out.println("i in subclass: " + i);
  }
}

class UseSuper {
  public static void main(String[] args) {
    B subOb = new B(1, 2);

    subOb.show();
  }
}

// -----------------------------------------

// Try This 7-1
//
// Build a subclass of Vehicle for trucks.
class Vehicle {
  private int passengers; // number of passengers
  private int fuelCap;    // fuel capacity in gallons
  private int mpg;        // fuel consumption in miles per gallon

  // This is a constructor for Vehicle.
  Vehicle(int p, int f, int m) {
    passengers = p;
    fuelCap = f;
    mpg = m;
  }

  // Return the range.
  int range() {
    return mpg * fuelCap;
  }

  // Compute fuel needed for a given distance.
  double fuelNeeded(int miles) {
    return (double) miles / mpg;
  }

  // Accessor methods for instance variables.
  int getPassengers() { return passengers; }
  void setPassengers(int p) { passengers = p; }

  int getFuelCap() { return fuelCap; }
  void setFuelCap(int f) { fuelCap = f; }

  int getMpg() { return mpg; }
  void setMpg(int m) { mpg = m; }
}

// Extend Vehicle to create a Truck specialization.
class Truck extends Vehicle {
  private int cargoCap; // cargo capacity in pounds

  // This is a constructor for Truck.
  Truck(int p, int f, int m, int c) {
    /* Initialize Vehicle members using
       Vehicle's constructor. */
    super(p, f, m);

    cargoCap = c;
  }

  // Accessor methods for cargoCap.
  int getCargo() { return cargoCap; }
  void putCargo(int c) { cargoCap = c; }
}

class TruckDemo {
  public static void main(String[] args) {

    // construct some trucks
    Truck semi = new Truck(2, 200, 7, 44000);
    Truck pickup = new Truck(3, 28, 15, 2000);
    double gallons;
    int dist = 252;

    gallons = semi.fuelNeeded(dist);

    System.out.println("Semi can carry " + semi.getCargo() +
                       " pounds.");
    System.out.println("To go " + dist + " miles semi needs " +
                       gallons + " gallons of fuel.\n");

    gallons = pickup.fuelNeeded(dist);

    System.out.println("Pickup can carry " + pickup.getCargo() +
                       " pounds.");
    System.out.println("To go " + dist + " miles pickup needs " +
                       gallons + " gallons of fuel.");
  }
}

// -----------------------------------------

// A multilevel hierarchy.
class TwoDShape {
  private double width;
  private double height;

  // A default constructor.
  TwoDShape() {
    width = height = 0.0;
  }

  // Parameterized constructor.
  TwoDShape(double w, double h) {
    width = w;
    height = h;
  }

  // Construct object with equal width and height.
  TwoDShape(double x) {
    width = height = x;
  }

  // Accessor methods for width and height.
  double getWidth() { return width; }
  double getHeight() { return height; }
  void setWidth(double w) { width = w; }
  void setHeight(double h) { height = h; }

  void showDim() {
    System.out.println("Width and height are " +
                       width + " and " + height);
  }
}

// Extend TwoDShape.
class Triangle extends TwoDShape {
  private String style;

  // A default constructor.
  Triangle() {
    super();
    style = "none";
  }

  Triangle(String s, double w, double h) {
    super(w, h); // call superclass constructor

    style = s;
  }

  // One argument constructor.
  Triangle(double x) {
    super(x); // call superclass constructor

    // default style to filled
    style = "filled";
  }

  double area() {
    return getWidth() * getHeight() / 2;
  }

  void showStyle() {
    System.out.println("Triangle is " + style);
  }
}

// Extend Triangle.
class ColorTriangle extends Triangle {
  private String color;

  ColorTriangle(String c, String s,
                double w, double h) {
    super(s, w, h);

    color = c;
  }

  String getColor() { return color; }

  void showColor() {
    System.out.println("Color is " + color);
  }
}

class Shapes6 {
  public static void main(String[] args) {
    ColorTriangle t1 =
         new ColorTriangle("Blue", "outlined", 8.0, 12.0);
    ColorTriangle t2 =
         new ColorTriangle("Red", "filled", 2.0, 2.0);

    System.out.println("Info for t1: ");
    t1.showStyle();
    t1.showDim();
    t1.showColor();
    System.out.println("Area is " + t1.area());

    System.out.println();

    System.out.println("Info for t2: ");
    t2.showStyle();
    t2.showDim();
    t2.showColor();
    System.out.println("Area is " + t2.area());
  }
}

// -----------------------------------------

// Demonstrate when constructors are executed.

// Create a super class.
class A {
  A() {
    System.out.println("Constructing A.");
  }
}

// Create a subclass by extending class A.
class B extends A {
  B() {
    System.out.println("Constructing B.");
  }
}

// Create another subclass by extending B.
class C extends B {
  C() {
    System.out.println("Constructing C.");
  }
}

class OrderOfConstruction {
  public static void main(String[] args) {
    C c = new C();
  }
}

// -----------------------------------------

// This will not compile.
class X {
  int a;

  X(int i) { a = i; }
}

class Y {
  int a;

  Y(int i) { a = i; }
}

class IncompatibleRef {
  public static void main(String[] args) {
    X x = new X(10);
    X x2;
    Y y = new Y(5);

    x2 = x; // OK, both of same type

    x2 = y; // Error, not of same type
  }
}

// -----------------------------------------

// A superclass reference can refer to a subclass object.
class X {
  int a;

  X(int i) { a = i; }
}

class Y extends X {
  int b;

  Y(int i, int j) {
    super(j);
    b = i;
  }
}

class SupSubRef {
  public static void main(String[] args) {
    X x = new X(10);
    X x2;
    Y y = new Y(5, 6);

    x2 = x; // OK, both of same type
    System.out.println("x2.a: " + x2.a);

    x2 = y; // still OK because y is derived from X
    System.out.println("x2.a: " + x2.a);

    // X references know only about X members
    x2.a = 19; // OK
//  x2.b = 27; // Error, X doesn't have a b member
  }
}

// -----------------------------------------

class TwoDShape {
  private double width;
  private double height;

  // A default constructor.
  TwoDShape() {
    width = height = 0.0;
  }

  // Parameterized constructor.
  TwoDShape(double w, double h) {
    width = w;
    height = h;
  }

  // Construct an object with equal width and height.
  TwoDShape(double x) {
    width = height = x;
  }

  // Construct an object from an object.
  TwoDShape(TwoDShape ob) {
    width = ob.width;
    height = ob.height;
  }

  // Accessor methods for width and height.
  double getWidth() { return width; }
  double getHeight() { return height; }
  void setWidth(double w) { width = w; }
  void setHeight(double h) { height = h; }

  void showDim() {
    System.out.println("Width and height are " +
                       width + " and " + height);
  }
}

// A subclass of TwoDShape for triangles.
class Triangle extends TwoDShape {
  private String style;

  // A default constructor.
  Triangle() {
    super();
    style = "none";
  }

  // Constructor for Triangle.
  Triangle(String s, double w, double h) {
    super(w, h); // call superclass constructor

    style = s;
  }

  // One argument constructor.
  Triangle(double x) {
    super(x); // call superclass constructor

    // default style to filled
    style = "filled";
  }

  // Construct an object from an object.
  Triangle(Triangle ob) {
    super(ob); // pass object to TwoDShape constructor
    style = ob.style;
  }

  double area() {
    return getWidth() * getHeight() / 2;
  }

  void showStyle() {
    System.out.println("Triangle is " + style);
  }
}

class Shapes7 {
  public static void main(String[] args) {
    Triangle t1 =
         new Triangle("outlined", 8.0, 12.0);

    // make a copy of t1
    Triangle t2 = new Triangle(t1);

    System.out.println("Info for t1: ");
    t1.showStyle();
    t1.showDim();
    System.out.println("Area is " + t1.area());

    System.out.println();

    System.out.println("Info for t2: ");
    t2.showStyle();
    t2.showDim();
    System.out.println("Area is " + t2.area());
  }
}

// -----------------------------------------

// Method overriding.
class A {
  int i, j;
  A(int a, int b) {
    i = a;
    j = b;
  }

  // display i and j
  void show() {
    System.out.println("i and j: " + i + " " + j);
  }
}

class B extends A {
  int k;

  B(int a, int b, int c) {
    super(a, b);
    k = c;
  }

  // display k - this overrides show() in A
  void show() {
    System.out.println("k: " + k);
  }
}

class Override {
  public static void main(String[] args) {
    B subOb = new B(1, 2, 3);

    subOb.show(); // this calls show() in B
  }
}

// -----------------------------------------

class B extends A {
  int k;

  B(int a, int b, int c) {
    super(a, b);
    k = c;
  }

  void show() {
    super.show(); // this calls A's show()
    System.out.println("k: " + k);
  }
}

// -----------------------------------------

/* Methods with differing signatures are
   overloaded and not overridden. */
class A {
  int i, j;

  A(int a, int b) {
    i = a;
    j = b;
  }

  // display i and j
  void show() {
    System.out.println("i and j: " + i + " " + j);
  }
}

// Create a subclass by extending class A.
class B extends A {
  int k;

  B(int a, int b, int c) {
    super(a, b);
    k = c;
  }

  // overload show()
  void show(String msg) {
    System.out.println(msg + k);
  }
}

class Overload {
  public static void main(String[] args) {
    B subOb = new B(1, 2, 3);

    subOb.show("This is k: "); // this calls show() in B
    subOb.show(); // this calls show() in A
  }
}

// -----------------------------------------

// Demonstrate dynamic method dispatch.

class Sup {
  void who() {
    System.out.println("who() in Sup");
  }
}

class Sub1 extends Sup {
  void who() {
    System.out.println("who() in Sub1");
  }
}

class Sub2 extends Sup {
  void who() {
    System.out.println("who() in Sub2");
  }
}

class DynDispDemo {
  public static void main(String[] args) {
    Sup superOb = new Sup();
    Sub1 subOb1 = new Sub1();
    Sub2 subOb2 = new Sub2();

    Sup supRef;

    supRef = superOb;
    supRef.who();

    supRef = subOb1;
    supRef.who();

    supRef = subOb2;
    supRef.who();
  }
}

// -----------------------------------------

// Use dynamic method dispatch.
class TwoDShape {
  private double width;
  private double height;
  private String name;

  // A default constructor.
  TwoDShape() {
    width = height = 0.0;
    name = "none";
  }

  // Parameterized constructor.
  TwoDShape(double w, double h, String n) {
    width = w;
    height = h;
    name = n;
  }

  // Construct object with equal width and height.
  TwoDShape(double x, String n) {
    width = height = x;
    name = n;
  }

  // Construct an object from an object.
  TwoDShape(TwoDShape ob) {
    width = ob.width;
    height = ob.height;
    name = ob.name;
  }

  // Accessor methods for width and height.
  double getWidth() { return width; }
  double getHeight() { return height; }
  void setWidth(double w) { width = w; }
  void setHeight(double h) { height = h; }

  String getName() { return name; }

  void showDim() {
    System.out.println("Width and height are " +
                       width + " and " + height);
  }

  double area() {
    System.out.println("area() must be overridden");
    return 0.0;
  }
}

// A subclass of TwoDShape for triangles.
class Triangle extends TwoDShape {
  private String style;

  // A default constructor.
  Triangle() {
    super();
    style = "none";
  }

  // Constructor for Triangle.
  Triangle(String s, double w, double h) {
    super(w, h, "triangle");

    style = s;
  }

  // One argument constructor.
  Triangle(double x) {
    super(x, "triangle"); // call superclass constructor

    // default style to filled
    style = "filled";
  }

  // Construct an object from an object.
  Triangle(Triangle ob) {
    super(ob); // pass object to TwoDShape constructor
    style = ob.style;
  }

  // Override area() for Triangle.
  double area() {
    return getWidth() * getHeight() / 2;
  }

  void showStyle() {
    System.out.println("Triangle is " + style);
  }
}

// A subclass of TwoDShape for rectangles.
class Rectangle extends TwoDShape {
  // A default constructor.
  Rectangle() {
    super();
  }

  // Constructor for Rectangle.
  Rectangle(double w, double h) {
    super(w, h, "rectangle"); // call superclass constructor
  }

  // Construct a square.
  Rectangle(double x) {
    super(x, "rectangle"); // call superclass constructor
  }

  // Construct an object from an object.
  Rectangle(Rectangle ob) {
    super(ob); // pass object to TwoDShape constructor
  }

  boolean isSquare() {
    if(getWidth() == getHeight()) return true;
    return false;
  }

  // Override area() for Rectangle.
  double area() {
    return getWidth() * getHeight();
  }
}

class DynShapes {
  public static void main(String[] args) {
    TwoDShape[] shapes = new TwoDShape[5];

    shapes[0] = new Triangle("outlined", 8.0, 12.0);
    shapes[1] = new Rectangle(10);
    shapes[2] = new Rectangle(10, 4);
    shapes[3] = new Triangle(7.0);
    shapes[4] = new TwoDShape(10, 20, "generic");

    for(TwoDShape shape : shapes) {
      System.out.println("object is " + shape.getName());
      System.out.println("Area is " + shape.area());
      System.out.println();
    }
  }
}

// -----------------------------------------

// Create an abstract class.
abstract class TwoDShape {
  private double width;
  private double height;
  private String name;

  // A default constructor.
  TwoDShape() {
    width = height = 0.0;
    name = "none";
  }

  // Parameterized constructor.
  TwoDShape(double w, double h, String n) {
    width = w;
    height = h;
    name = n;
  }

  // Construct object with equal width and height.
  TwoDShape(double x, String n) {
    width = height = x;
    name = n;
  }

  // Construct an object from an object.
  TwoDShape(TwoDShape ob) {
    width = ob.width;
    height = ob.height;
    name = ob.name;
  }

  // Accessor methods for width and height.
  double getWidth() { return width; }
  double getHeight() { return height; }
  void setWidth(double w) { width = w; }
  void setHeight(double h) { height = h; }

  String getName() { return name; }

  void showDim() {
    System.out.println("Width and height are " +
                       width + " and " + height);
  }

  // Now, area() is abstract.
  abstract double area();
}

// A subclass of TwoDShape for triangles.
class Triangle extends TwoDShape {
  private String style;

  // A default constructor.
  Triangle() {
    super();
    style = "none";
  }

  // Constructor for Triangle.
  Triangle(String s, double w, double h) {
    super(w, h, "triangle");

    style = s;
  }

  // One argument constructor.
  Triangle(double x) {
    super(x, "triangle"); // call superclass constructor

    // default style to filled
    style = "filled";
  }

  // Construct an object from an object.
  Triangle(Triangle ob) {
    super(ob); // pass object to TwoDShape constructor
    style = ob.style;
  }

  double area() {
    return getWidth() * getHeight() / 2;
  }

  void showStyle() {
    System.out.println("Triangle is " + style);
  }
}

// A subclass of TwoDShape for rectangles.
class Rectangle extends TwoDShape {
  // A default constructor.
  Rectangle() {
    super();
  }

  // Constructor for Rectangle.
  Rectangle(double w, double h) {
    super(w, h, "rectangle"); // call superclass constructor
  }

  // Construct a square.
  Rectangle(double x) {
    super(x, "rectangle"); // call superclass constructor
  }

  // Construct an object from an object.
  Rectangle(Rectangle ob) {
    super(ob); // pass object to TwoDShape constructor
  }

  boolean isSquare() {
    if(getWidth() == getHeight()) return true;
    return false;
  }

  double area() {
    return getWidth() * getHeight();
  }
}

class AbsShape {
  public static void main(String[] args) {
    TwoDShape[] shapes = new TwoDShape[4];

    shapes[0] = new Triangle("outlined", 8.0, 12.0);
    shapes[1] = new Rectangle(10);
    shapes[2] = new Rectangle(10, 4);
    shapes[3] = new Triangle(7.0);

    for(TwoDShape shape : shapes) {
      System.out.println("object is " + shape.getName());
      System.out.println("Area is " + shape.area());
      System.out.println();
    }
  }
}

// -----------------------------------------

class A {
  final void meth() {
    System.out.println("This is a final method.");
  }
}

class B extends A {
  void meth() { // ERROR! Can't override.
    System.out.println("Illegal!");
  }
}

// -----------------------------------------

final class A {
  // ...
}

// The following class is illegal.
class B extends A { // ERROR! Can't subclass A
  // ...
}

// -----------------------------------------

// Return a String object.
class ErrorMsg {
  // Error codes.
  final int OUTERR   = 0;
  final int INERR    = 1;
  final int DISKERR  = 2;
  final int INDEXERR = 3;

  String[] msgs = {
    "Output Error",
    "Input Error",
    "Disk Full",
    "Index Out-Of-Bounds"
  };

  // Return the error message.
  String getErrorMsg(int i) {
    if(i >=0 & i < msgs.length)
      return msgs[i];
    else
      return "Invalid Error Code";
  }
}

class FinalD {
  public static void main(String[] args) {
    ErrorMsg err = new ErrorMsg();

    System.out.println(err.getErrorMsg(err.OUTERR));
    System.out.println(err.getErrorMsg(err.DISKERR));
  }
}