Chapter 20 new exercise solutions

ch_20/exercise20_04/CompareY.java

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+package ch_20.exercise20_04;
+
+import java.util.Comparator;
+
+/**
+ * Define a class named CompareY that implements Comparator<Point>.
+ * Implement the compare method to compare two points on their y-coordinates.
+ * If two points have the same y-coordinates, compare their x-coordinates.
+ */
+public class CompareY implements Comparator<Point> {
+    @Override
+    public int compare(Point p1, Point p2) {
+        int resultY;
+        if (p1.y < p2.y) {
+            resultY = -1;
+        } else if (p1.y > p2.y) {
+            resultY = 1;
+        } else {
+            resultY = 0;
+        }
+        if (resultY == 0) {
+            if (p1.x < p2.x) {
+                return -1;
+            }
+            if (p1.x > p2.x) {
+                return 1;
+            }
+            return 0;
+        }
+        return resultY;
+    }
+}

ch_20/exercise20_04/Exercise20_04.java

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+package ch_20.exercise20_04;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.Random;
+
+/**
+ * *20.4 (Sort points in a plane) Write a program that meets the following requirements:
+ * ■ Define a class named Point with two data fields x and y to represent a
+ * point’s x- and y-coordinates. Implement the Comparable interface for comparing the points on x-coordinates.
+ * If two points have the same x-coordinates, compare their y-coordinates.
+ * ■ Define a class named CompareY that implements Comparator<Point>.
+ * Implement the compare method to compare two points on their y-coordinates.
+ * If two points have the same y-coordinates, compare their x-coordinates.
+ * ■ Randomly create 100 points and apply the Arrays.sort method to display
+ * the points in increasing order of their x-coordinates and in increasing order
+ * of their y-coordinates, respectively.
+ */
+public class Exercise20_04 {
+    private static Point[] points = new Point[100];
+    private static CompareY comparator = new CompareY();
+
+    public static void main(String[] args) {
+        Random randomPoint = new Random();
+        for (int i = 0; i < points.length; i++) {
+            points[i] = new Point(randomPoint.nextDouble() * randomPoint.nextInt(999), randomPoint.nextDouble() * randomPoint.nextInt(999));
+        }
+        System.out.println("Created 100 Random Points: ");
+        for (Point point : points) {
+            System.out.print(point.toString());
+        }
+
+        System.out.println("Increasing order by the x-coordinates: ");
+        Arrays.sort(points);
+        for (Point point : points) {
+            System.out.print(point.toString());
+        }
+
+        System.out.println("Increasing order by the y-coordinates: ");
+        Arrays.sort(points, comparator);
+        for (Point point : points) {
+            System.out.print(point.toString());
+        }
+    }
+}

ch_20/exercise20_04/Point.java

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+package ch_20.exercise20_04;
+
+/**
+ * ■ Define a class named Point with two data fields x and y to represent a
+ * * point’s x- and y-coordinates.
+ * Implement the Comparable interface for comparing the points on x-coordinates.
+ * If two points have the same x-coordinates, compare their y-coordinates.
+ */
+public class Point implements Comparable<Point> {
+    double x;
+    double y;
+
+    public Point(double x, double y) {
+        this.x = x;
+        this.y = y;
+    }
+
+    public double getX() {
+        return x;
+    }
+
+    public Point setX(double x) {
+        this.x = x;
+        return this;
+    }
+
+    public double getY() {
+        return y;
+    }
+
+    public Point setY(double y) {
+        this.y = y;
+        return this;
+    }
+
+
+    @Override
+    public String toString() {
+        return "Point{" +
+                "x=" + x +
+                ", y=" + y +
+                "}\n";
+    }
+
+    @Override
+    public int compareTo(Point that) {
+        if (this.x == that.x) {
+            if (this.y < that.y) {
+                return -1;
+            }
+            if (this.y > that.y) {
+                return 1;
+            }
+            return 0; // this.y == that.y
+
+        } else {
+            if (this.x < that.x) {
+                return -1;
+            }
+            if (this.x > that.x) {
+                return 1;
+            }
+            return 0;//this.x == that.x
+
+        }
+
+    }
+
+}