Transforming an ADT into java interface

Problem:

Implement the ADT below:
ADT: Polynomial
degree(): int
derivative(): Polynomial
equals(Point): Boolean
sum(Polynomial): Polynomial
toString(): String
valueAt(Real): Real

Output:

Not applicable.

Solution:

public class MyPolynomial implements Polynomial {
 private double[] c; // coefficients
 public MyPolynomial(double[] a) { // a[i] = coeffficient of x^i
 int n = c.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];
 }
 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(" + %.2f", c[1]));
 }
for (int i=2; i<n; i++) {
 if (c[i] != 0.0) {
 buf.append(String.format(" + %.2f^%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;
 }
}

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How to implement an ADT in Java

Problem:

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

Output:

Not applicable.

Solution:

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 == 0.0;
 }
 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;
 }
}

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Implement the ADT with a Java Example

Problem:

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

Output:

Not applicable.

Solution:

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;
 }
}

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