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chapter 20 Exercise 22 + 23
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‎ch_20/Exercise20_21.java

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package ch_20;
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import java.util.Arrays;
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import java.util.Comparator;
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/**
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* 20.21 (Use Comparator) Write the following generic method using selection sort
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* and a comparator.
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* public static <E> void selectionSort(E[] list, Comparator<? super E> comparator)
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* <p>
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* Write a test program that creates an array of 10 GeometricObjects and
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* invokes this method using the GeometricObjectComparator introduced in
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* Listing 20.4 to sort the elements. Display the sorted elements. Use the following statement to create the array.
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* GeometricObject[] list = {new Circle(5), new Rectangle(4, 5),
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* new Circle(5.5), new Rectangle(2.4, 5), new Circle(0.5),
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* new Rectangle(4, 65), new Circle(4.5), new Rectangle(4.4, 1),
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* new Circle(6.5), new Rectangle(4, 5)};
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*/
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public class Exercise20_21 {
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public static void main(String[] args) {
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GeometricObject[] list = {new Circle(5), new Rectangle(4, 5),
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new Circle(5.5), new Rectangle(2.4, 5), new Circle(0.5),
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new Rectangle(4, 65), new Circle(4.5), new Rectangle(4.4, 1),
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new Circle(6.5), new Rectangle(4, 5)};
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selectionSort(list, new GeometricObjectComparator());
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for (int i = 0; i < list.length; i++) {
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System.out.println("Area of GeometricObject: list[" + i + "] = " + list[i].getArea());
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}
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}
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public static <E> void selectionSort(E[] list,
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Comparator<? super E> comparator) {
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for (int i = 0; i < list.length - 1; i++) {
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E currentMin = list[i];
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int currentMinIndex = i;
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for (int j = i + 1; j < list.length; j++) {
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if (comparator.compare(currentMin, list[j]) > 0) { // currentMin is greater than list at j
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currentMin = list[j];
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currentMinIndex = j;
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}
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}
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if (currentMinIndex != i) {
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list[currentMinIndex] = list[i];
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list[i] = currentMin;
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}
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}
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}
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}
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class GeometricObjectComparator
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implements Comparator<GeometricObject>, java.io.Serializable {
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public int compare(GeometricObject o1, GeometricObject o2) {
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double area1 = o1.getArea();
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double area2 = o2.getArea();
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if (area1 < area2)
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return -1;
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else if (area1 == area2)
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return 0;
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else
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return 1;
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}
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}
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class Circle extends GeometricObject {
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private double radius;
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public Circle() {
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}
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public Circle(double radius) {
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this.radius = radius;
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}
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public Circle(double radius, String color,
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boolean filled) {
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this.radius = radius;
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setColor(color);
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setFilled(filled);
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}
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public double getRadius() {
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return radius;
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}
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public void setRadius(double radius) {
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this.radius = radius;
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}
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@Override
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public double getArea() {
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return radius * radius * Math.PI;
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}
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@Override
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public double getPerimeter() {
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return 2 * radius * Math.PI;
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}
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@Override
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public String toString() {
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return super.toString() + "\nRadius: " + getRadius() + "\nArea: "
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+ getArea() + "\nPerimeter: " + getPerimeter();
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}
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}
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class Rectangle extends GeometricObject {
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private double width;
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private double height;
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public Rectangle() {
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width = 1;
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height = 1;
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}
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public Rectangle(double newWidth, double newHeight) {
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width = newWidth;
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height = newHeight;
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}
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public double getWidth() {
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return width;
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}
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public void setWidth(double width) {
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this.width = width;
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}
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public double getHeight() {
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return height;
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}
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public void setHeight(double height) {
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this.height = height;
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}
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@Override
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public double getArea() {
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double area = width * height;
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return area;
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}
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@Override
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public double getPerimeter() {
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return (2 * width) + (2 * height);
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}
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@Override
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public String toString() {
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return super.toString() + "\nWidth: " + width + "\nHeight: " + height
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+ "\nArea: " + getArea() + "\nPerimeter: " + getPerimeter();
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}
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}
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abstract class GeometricObject {
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private String color = "white";
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private boolean filled;
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private java.util.Date dateCreated;
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/**
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* Construct a default geometric object
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*/
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protected GeometricObject() {
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dateCreated = new java.util.Date();
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}
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/**
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* Construct a geometric object with color and filled value
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*/
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protected GeometricObject(String color, boolean filled) {
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dateCreated = new java.util.Date();
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this.color = color;
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this.filled = filled;
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}
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/**
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* Return color
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*/
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public String getColor() {
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return color;
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}
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/**
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* Set a new color
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*/
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public void setColor(String color) {
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this.color = color;
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}
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/**
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* Return filled. Since filled is boolean,
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* the get method is named isFilled
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*/
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public boolean isFilled() {
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return filled;
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}
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/**
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* Set a new filled
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*/
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public void setFilled(boolean filled) {
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this.filled = filled;
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}
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/**
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* Get dateCreated
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*/
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public java.util.Date getDateCreated() {
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return dateCreated;
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}
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@Override
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public String toString() {
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return "created on " + dateCreated + "\ncolor: " + color +
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" and filled: " + filled;
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}
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/**
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* Abstract method getArea
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*/
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public abstract double getArea();
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/**
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* Abstract method getPerimeter
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*/
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public abstract double getPerimeter();
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}

‎ch_20/Exercise20_23.java

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package ch_20;
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import java.util.Scanner;
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import java.util.Stack;
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/**
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* *20.23 (Evaluate expression) Modify Listing 20.9 EvaluateExpression.java to add
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* operators ^ for exponent and % for modulus. For example, 3 ^ 2 is 9 and 3 % 2
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* is 1. The ^ operator has the highest precedence and the % operator has the same
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* precedence as the * and / operators. Your program should prompt the user to
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* enter an expression. Here is a sample run of the program:
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* Enter an expression: (5 * 2 ^ 3 + 2 * 3 % 2) * 4
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* (5 * 2 ^ 3 + 2 * 3 % 2) * 4 = 160
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*/
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public class Exercise20_23 {
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public static void main(String[] args) {
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Scanner input = new Scanner(System.in);
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System.out.print("Enter an expression: ");
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String expression = input.nextLine();
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try {
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System.out.print(expression + " = ");
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System.out.print(evaluateExpression(expression));
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} catch (Exception ex) {
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System.out.println("Wrong expression: " + expression);
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}
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}
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/**
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* Evaluate an expression
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*/
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public static int evaluateExpression(String expression) {
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// Create operandStack to store operands
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Stack<Integer> operandStack = new Stack<>();
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// Create operatorStack to store operators
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Stack<Character> operatorStack = new Stack<>();
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// Pad following characters with space: (, ), +, -, /, *, ^ and %
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expression = insertBlanks(expression);
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// Extract operands and operators
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String[] tokens = expression.split(" ");
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// Phase 1: Scan tokens
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for (String token : tokens) {
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if (token.length() == 0) {
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continue;
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}
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if (token.charAt(0) == '^') {
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operatorStack.push(token.charAt(0));
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} else if (token.charAt(0) == '+' || token.charAt(0) == '-') {
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// Process all ^ in the top of the operator stack (has the highest precedence)
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while (!operatorStack.isEmpty() && operatorStack.peek() == '^') {
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processAnOperator(operandStack, operatorStack);
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}
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while (!operatorStack.isEmpty() &&
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token.charAt(0) == '*' ||
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token.charAt(0) == '/' ||
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token.charAt(0) == '%') {
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processAnOperator(operandStack, operatorStack);
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}
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// Push the + or - operator into the operator stack
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operatorStack.push(token.charAt(0));
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} else if (token.charAt(0) == '*' || token.charAt(0) == '/' || token.charAt(0) == '%') {
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while (!operatorStack.isEmpty() && operatorStack.peek() == '^') {
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processAnOperator(operandStack, operatorStack);
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}
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// Process all *, / , % in the top of the operator stack (same precedence)
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while (!operatorStack.isEmpty() &&
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(operatorStack.peek() == '*' ||
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operatorStack.peek() == '^' ||
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operatorStack.peek() == '/' ||
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operatorStack.peek() == '%')) {
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processAnOperator(operandStack, operatorStack);
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}
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// Push the *, /, or % operator into the operator stack
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operatorStack.push(token.charAt(0));
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} else if (token.trim().charAt(0) == '(') {
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operatorStack.push('('); // Push '(' to stack
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} else if (token.trim().charAt(0) == ')') {
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// Process all the operators in the stack until seeing '(
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while (operatorStack.peek() != '(') {
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processAnOperator(operandStack, operatorStack);
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}
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operatorStack.pop(); // Pop the '(' symbol from the stack
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} else { // An operand scanned
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// Push an operand to the stack
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operandStack.push(new Integer(token));
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}
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}
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// Phase 2: Process all the remaining operators in the stack
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while (!operatorStack.isEmpty()) {
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processAnOperator(operandStack, operatorStack);
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}
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// Return the result
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return operandStack.pop();
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}
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/**
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* Process one operator: Take an operator from operatorStack a
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* apply it on the operands in the operandStack
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*/
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public static void processAnOperator(
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Stack<Integer> operandStack, Stack<Character> operatorStack) {
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char op = operatorStack.pop();
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int op1 = operandStack.pop();
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int op2 = operandStack.pop();
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if (op == '+')
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operandStack.push(op2 + op1);
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else if (op == '-')
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operandStack.push(op2 - op1);
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else if (op == '*')
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operandStack.push(op2 * op1);
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else if (op == '/')
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operandStack.push(op2 / op1);
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else if (op == '^')
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operandStack.push((int) Math.pow(op2, op1)); // Exponent operation
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else if (op == '%')
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operandStack.push(op2 % op1);// Modulus operation
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}
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public static String insertBlanks(String s) {
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String result = "";
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for (int i = 0; i < s.length(); i++) {
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if (s.charAt(i) == '(' || s.charAt(i) == ')' ||
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s.charAt(i) == '+' || s.charAt(i) == '-' ||
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s.charAt(i) == '*' || s.charAt(i) == '/' ||
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s.charAt(i) == '^' || s.charAt(i) == '%') // Check for exponent and modulus operands.
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result += " " + s.charAt(i) + " ";
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else
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result += s.charAt(i);
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}
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return result;
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}
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}

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