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Abstract Classes and Interfaces (Chapter 18) -- examples from Liang Intro to Java Comprehensive 10e
import java.util.Scanner;
public class ComputeFactorial {
/** Main method */
public static void main(String[] args) {
// Create a Scanner
Scanner input = new Scanner(System.in);
System.out.print("Enter a non-negative integer: ");
int n = input.nextInt();
// Display factorial
System.out.println("Factorial of " + n + " is " + factorial(n));
}
/** Return the factorial for a specified number */
public static long factorial(int n) {
if (n == 0) // Base case
return 1;
else
return n * factorial(n - 1); // Recursive call
}
}
public class ComputeFactorialTailRecursion {
/** Return the factorial for a specified number */
public static long factorial(int n) {
return factorial(n, 1); // Call auxiliary method
}
/** Auxiliary tail-recursive method for factorial */
private static long factorial(int n, int result) {
if (n == 0)
return result;
else
return factorial(n - 1, n * result); // Recursive call
}
}
import java.util.Scanner;
public class ComputeFibonacci {
/** Main method */
public static void main(String[] args) {
// Create a Scanner
Scanner input = new Scanner(System.in);
System.out.print("Enter an index for a Fibonacci number: ");
int index = input.nextInt();
// Find and display the Fibonacci number
System.out.println("The Fibonacci number at index "
+ index + " is " + fib(index));
}
/** The method for finding the Fibonacci number */
public static long fib(long index) {
if (index == 0) // Base case
return 0;
else if (index == 1) // Base case
return 1;
else // Reduction and recursive calls
return fib(index - 1) + fib(index - 2);
}
}
import java.io.File;
import java.util.Scanner;
public class DirectorySize {
public static void main(String[] args) {
// Prompt the user to enter a directory or a file
System.out.print("Enter a directory or a file: ");
Scanner input = new Scanner(System.in);
String directory = input.nextLine();
// Display the size
System.out.println(getSize(new File(directory)) + " bytes");
}
public static long getSize(File file) {
long size = 0; // Store the total size of all files
if (file.isDirectory()) {
File[] files = file.listFiles(); // All files and subdirectories
for (int i = 0; files != null && i < files.length; i++) {
size += getSize(files[i]); // Recursive call
}
}
else { // Base case
size += file.length();
}
return size;
}
}
public class RecursiveBinarySearch {
public static int recursiveBinarySearch(int[] list, int key) {
int low = 0;
int high = list.length - 1;
return recursiveBinarySearch(list, key, low, high);
}
private static int recursiveBinarySearch(int[] list, int key,
int low, int high) {
if (low > high) // The list has been exhausted without a match
return -low - 1;
int mid = (low + high) / 2;
if (key < list[mid])
return recursiveBinarySearch(list, key, low, mid - 1);
else if (key == list[mid])
return mid;
else
return recursiveBinarySearch(list, key, mid + 1, high);
}
}
public class RecursiveSelectionSort {
public static void sort(double[] list) {
sort(list, 0, list.length - 1); // Sort the entire list
}
private static void sort(double[] list, int low, int high) {
if (low < high) {
// Find the smallest number and its index in list(low .. high)
int indexOfMin = low;
double min = list[low];
for (int i = low + 1; i <= high; i++) {
if (list[i] < min) {
min = list[i];
indexOfMin = i;
}
}
// Swap the smallest in list(low .. high) with list(low)
list[indexOfMin] = list[low];
list[low] = min;
// Sort the remaining list(low+1 .. high)
sort(list, low + 1, high);
}
}
public static void main(String[] args) {
double[] list = {2, 1, 3, 1, 2, 5, 2, -1, 0};
sort(list);
for (int i = 0; i < list.length; i++)
System.out.print(list[i] + " ");
}
}
import javafx.application.Application;
import javafx.geometry.Point2D;
import javafx.geometry.Pos;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.control.TextField;
import javafx.scene.layout.BorderPane;
import javafx.scene.layout.HBox;
import javafx.scene.layout.Pane;
import javafx.scene.paint.Color;
import javafx.scene.shape.Polygon;
import javafx.stage.Stage;
public class SierpinskiTriangle extends Application {
@Override // Override the start method in the Application class
public void start(Stage primaryStage) {
SierpinskiTrianglePane trianglePane = new SierpinskiTrianglePane();
TextField tfOrder = new TextField();
tfOrder.setOnAction(
e -> trianglePane.setOrder(Integer.parseInt(tfOrder.getText())));
tfOrder.setPrefColumnCount(4);
tfOrder.setAlignment(Pos.BOTTOM_RIGHT);
// Pane to hold label, text field, and a button
HBox hBox = new HBox(10);
hBox.getChildren().addAll(new Label("Enter an order: "), tfOrder);
hBox.setAlignment(Pos.CENTER);
BorderPane borderPane = new BorderPane();
borderPane.setCenter(trianglePane);
borderPane.setBottom(hBox);
// Create a scene and place it in the stage
Scene scene = new Scene(borderPane, 200, 210);
primaryStage.setTitle("SierpinskiTriangle"); // Set the stage title
primaryStage.setScene(scene); // Place the scene in the stage
primaryStage.show(); // Display the stage
scene.widthProperty().addListener(ov -> trianglePane.paint());
scene.heightProperty().addListener(ov -> trianglePane.paint());
}
/** Pane for displaying triangles */
static class SierpinskiTrianglePane extends Pane {
private int order = 0;
/** Set a new order */
public void setOrder(int order) {
this.order = order;
paint();
}
SierpinskiTrianglePane() {
}
protected void paint() {
// Select three points in proportion to the panel size
Point2D p1 = new Point2D(getWidth() / 2, 10);
Point2D p2 = new Point2D(10, getHeight() - 10);
Point2D p3 = new Point2D(getWidth() - 10, getHeight() - 10);
this.getChildren().clear(); // Clear the pane before redisplay
displayTriangles(order, p1, p2, p3);
}
private void displayTriangles(int order, Point2D p1,
Point2D p2, Point2D p3) {
if (order == 0) {
// Draw a triangle to connect three points
Polygon triangle = new Polygon();
triangle.getPoints().addAll(p1.getX(), p1.getY(), p2.getX(),
p2.getY(), p3.getX(), p3.getY());
triangle.setStroke(Color.BLACK);
triangle.setFill(Color.WHITE);
this.getChildren().add(triangle);
}
else {
// Get the midpoint on each edge in the triangle
Point2D p12 = p1.midpoint(p2);
Point2D p23 = p2.midpoint(p3);
Point2D p31 = p3.midpoint(p1);
// Recursively display three triangles
displayTriangles(order - 1, p1, p12, p31);
displayTriangles(order - 1, p12, p2, p23);
displayTriangles(order - 1, p31, p23, p3);
}
}
}
/**
* The main method is only needed for the IDE with limited
* JavaFX support. Not needed for running from the command line.
*/
public static void main(String[] args) {
launch(args);
}
}
import java.util.Scanner;
public class TowerOfHanoi {
/** Main method */
public static void main(String[] args) {
// Create a Scanner
Scanner input = new Scanner(System.in);
System.out.print("Enter number of disks: ");
int n = input.nextInt();
// Find the solution recursively
System.out.println("The moves are:");
moveDisks(n, 'A', 'B', 'C');
}
/** The method for finding the solution to move n disks
from fromTower to toTower with auxTower */
public static void moveDisks(int n, char fromTower,
char toTower, char auxTower) {
if (n == 1) // Stopping condition
System.out.println("Move disk " + n + " from " +
fromTower + " to " + toTower);
else {
moveDisks(n - 1, fromTower, auxTower, toTower);
System.out.println("Move disk " + n + " from " +
fromTower + " to " + toTower);
moveDisks(n - 1, auxTower, toTower, fromTower);
}
}
}
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