学习笔记——数据结构学习指导与习题解答

将下面的ADT转换成Java接口并用一个Java类实现：

ADT：Point
amplitude():Real
distanceTo(Point):Real
equals(Point):Boolean
magnitude():Real
toString():String
xCoordinate():Real
yCoordinate():Real

ADT：Line
contains(Point):Boolean
equals(Line):Boolean
isHorizontal():Boolean
isVertical():Boolean
slope():Real
toString():String
xIntercept():Real
yIntercept():Real

ADT:Circle
area():Real
center():Point
circumference():Real
contains(Point):Boolean
equals(Circle):Boolean
radius():Real
toString():String

ADT:Polynomial
derivative():Polynomial
equals(Polynomial):Boolean
sum(Polynomial):Polynomial
toString():String
valueAt(Real):Real

Java接口：

public interface Point {
	public double amplitude();
	public double distanceTo(Point point);
	public boolean equals(Object object);
	public double magnitude();
	public String toString();
	public double xCoordinate();
	public double yCoordinate();
}

public interface Line {
	public boolean contains(Point point);
	public boolean equals(Object object);
	public boolean isHorizontal();
	public boolean isVertical();
	public double slope();
	public String toString();
	public double xIntercept();
	public double yIntercept();	
}

public interface Circle {
	public double area();
	public Point center();
	public double circumference();
	public boolean contains(Point point);
	public boolean equals(Object object);
	public double radius();
	public String toString();
}

public interface Polynomial {
	public int degree();
	public Polynomial derivative();
	public boolean equals(Object object);
	public Polynomial sum(Polynomial polynomial);
	public String toString();
	public double valueAt(double x);
}

Java类：

public class MyPoint implements Point {
	private double x, y;
	public static Point ORIGIN = new MyPoint();

	private MyPoint() {
	}

	public MyPoint(double x, double y) {
		this.x = x;
		this.y = y;
	}

	public double amplitude() {
		return Math.atan(y / x);
	}

	public double distanceTo(Point point) {
		if (point.equals(this)) {
			return 0.0;
		} else if (!(point instanceof MyPoint)) {
			throw new IllegalArgumentException("use a MyPoint object");
		} else {
			MyPoint that = (MyPoint) point;
			double dx = that.x - this.x;
			double dy = that.y - this.y;
			return Math.sqrt(dx * dx + dy * dy);
		}
	}

	public boolean equals(Object object) {
		if (object == this) {
			return true;
		} else if (!(object instanceof MyPoint)) {
			return false;
		}
		MyPoint that = (MyPoint) object;
		return (that.x == this.x && that.y == this.y);
	}

	public double magnitude() {
		return Math.sqrt(x * x + y * y);
	}

	public String toString() {
		return String.format("(%.2f,%.2f)", x, y);
	}

	public double xCoordinate() {
		return x;
	}

	public double yCoordinate() {
		return y;
	}
}

public class MyLine implements Line {
	private double m, b; // slope,intercept
	public static Line X_AXIS = new MyLine();

	private MyLine() {
	}

	public MyLine(double m, double b) {
		this.m = m;
		this.b = b;
	}

	public boolean contains(Point point) {
		double x = point.xCoordinate();
		double y = point.yCoordinate();
		return y == m * x + b;
	}

	public boolean equals(Object object) {
		if (object == this) {
			return true;
		} else if (!(object instanceof MyLine)) {
			return false;
		}
		MyLine that = (MyLine) object;
		return (that.m == this.m && that.b == this.b);
	}

	public boolean isHorizontal() {
		return m == 0;
	}

	public boolean isVertical() {
		return m == Double.POSITIVE_INFINITY || m == Double.NEGATIVE_INFINITY;
	}

	public double slope() {
		return m;
	}

	public String toString() {
		return String.format("y=%.2fx+%.2f", m, b);
	}

	public double xIntercept() {
		if (isHorizontal()) {
			throw new RuntimeException("this line is horizontal");
		}
		return -b / m;
	}

	public double yIntercept() {
		if (isVertical()) {
			throw new RuntimeException("this line is vertical");
		}
		return b;
	}
}

public class MyCircle implements Circle {
	private Point c; // center
	private double r; // radius

	public MyCircle() {
	}

	public MyCircle(Point c, double r) {
		this.c = c;
		this.r = r;
	}

	public double area() {
		return Math.PI * r * r;
	}

	public Point center() {
		return c;
	}

	public double circumference() {
		return 2 * Math.PI * r;
	}

	public boolean contains(Point point) {
		double x = point.xCoordinate();
		double y = point.yCoordinate();
		return (x-c.xCoordinate()) * (x-c.xCoordinate()) + (y-c.yCoordinate()) * (y-c.yCoordinate()) < r * r;
	}

	public boolean equals(Object object) {
		if (object == this) {
			return true;
		} else if (!(object instanceof MyCircle)) {
			return false;
		}
		MyCircle that = (MyCircle) object;
		return (that.c == this.c && that.r == this.r);
	}

	public double radius() {
		return r;
	}

	public String toString() {
		return String.format("[Center:%s;Radius:%.2f]", c, r);
	}
}

public class MyPolynomial implements Polynomial {
	private double[] c; // coefficients

	public MyPolynomial(double[] a) { // a[i]=coefficient of x^i
		int n = a.length;
		c = new double[n];
		System.arraycopy(a, 0, c, 0, n);
	}

	public int degree() {
		return c.length - 1;
	}

	public Polynomial derivative() {
		double[] da = new double[c.length - 1];
		for (int i = 0; i < da.length; i++) {
			da[i] = (i + 1) * c[i + 1];
		}
		return new MyPolynomial(da);
	}

	public boolean equals(Object object) {
		if (object == this) {
			return true;
		} else if (!(object instanceof MyPolynomial)) {
			return false;
		}
		MyPolynomial that = (MyPolynomial) object;
		return java.util.Arrays.equals(that.c, this.c);
	}

	public Polynomial sum(Polynomial p) {
		if (!(p instanceof MyPolynomial)) {
			throw new IllegalArgumentException("use a MyPolynomial object");
		}
		MyPolynomial that = (MyPolynomial) p;
		double[] pc = that.c;
		int n = Math.max(c.length, pc.length);
		MyPolynomial q = new MyPolynomial(new double[n]);
		for (int i = 0; i < n; i++) {
			q.c[i] = c[i] + pc[i]; //这里有个问题，如果两个MyPolynomial对象的c长度不一样，会报错Exception in thread "main" java.lang.ArrayIndexOutofBoundsException:5
		}
		return q;
	}

	public String toString() {
		StringBuilder buf = new StringBuilder();
		int n = c.length;
		if (n > 0 && c[0] != 0.0) {
			buf.append(c[0]);
		}
		if (n > 1 && c[1] != 0.0) {
			buf.append(String.format("+%.2fx", c[1]));
		}
		for (int i = 2; i < n; i++) {
			if (c[i] != 0.0) {
				buf.append(String.format("+%.2fx^%d", c[i], i));
			}
		}
		return buf.toString();
	}

	public double valueAt(double x) {
		double y = 0.0;
		for (int i = 0; i < c.length; i++) {
			y += c[i] * Math.pow(x, i);
		}
		return y;
	}
}