Java语言程序设计与数据结构（基础篇）第17章课后习题代码chapter17.rar

import java.io.*; import javafx.application.Application; import javafx.geometry.Pos; import javafx.scene.Scene; import javafx.scene.control.Button; import javafx.scene.control.Label; import javafx.scene.control.TextField; import javafx.scene.layout.BorderPane; import javafx.scene.layout.GridPane; import javafx.scene.layout.HBox; import javafx.stage.Stage; public class Exercise17_09 extends Application { // Specify the size of five string fields in the record final static int NAME_SIZE = 32; final static int STREET_SIZE = 32; final static int CITY_SIZE = 20; final static int STATE_SIZE = 2; final static int ZIP_SIZE = 5; final static int RECORD_SIZE = (NAME_SIZE + STREET_SIZE + CITY_SIZE + STATE_SIZE + ZIP_SIZE); // Access address.dat using RandomAccessFile private RandomAccessFile raf; // Text fields private TextField tfName = new TextField(); private TextField tfStreet = new TextField(); private TextField tfCity = new TextField(); private TextField tfState = new TextField(); private TextField tfZip = new TextField(); // Buttons private Button btAdd = new Button("Add"); private Button btFirst = new Button("First"); private Button btNext = new Button("Next"); private Button btPrevious = new Button("Previous"); private Button btLast = new Button("Last"); private Button btUpdate = new Button("Update"); public Exercise17_09() { // Open or create a random access file try { raf = new RandomAccessFile("address.dat", "rw"); } catch(IOException ex) { ex.printStackTrace(); System.exit(1); } } @Override public void start(Stage primaryStage) { tfState.setPrefColumnCount(2); tfZip.setPrefColumnCount(4); tfCity.setPrefColumnCount(12); // Pane p1 for holding labels Name, Street, and City GridPane p1 = new GridPane(); p1.setAlignment(Pos.CENTER); p1.setHgap(5); p1.setVgap(5); p1.add(new Label("Name"), 0, 0); p1.add(new Label("Street"), 0, 1); p1.add(new Label("City"), 0, 2); p1.add(tfName, 1, 0); p1.add(tfStreet, 1, 1); HBox p2 = new HBox(5); p2.getChildren().addAll(tfCity, new Label("State"), tfState, new Label("Zip"), tfZip); p1.add(p2, 1, 2); // Add buttons to a pane HBox p3 = new HBox(5); p3.getChildren().addAll(btAdd, btFirst, btNext, btPrevious, btLast, btUpdate); p3.setAlignment(Pos.CENTER); // Add p1 and p3 to a border pane BorderPane borderPane = new BorderPane(); borderPane.setCenter(p1); borderPane.setBottom(p3); // Create a scene and place it in the stage Scene scene = new Scene(borderPane, 400, 120); primaryStage.setTitle("Exercise17_09"); // Set the stage title primaryStage.setScene(scene); // Place the scene in the stage primaryStage.show(); // Display the stage // Display the first record if exists try { if (raf.length() > 0) readAddress(0); } catch (IOException ex) { ex.printStackTrace(); } btAdd.setOnAction(e -> { try { writeAddress(raf.length()); } catch (Exception ex) { } }); btFirst.setOnAction(e -> { try { if (raf.length() > 0) readAddress(0); } catch (IOException ex) { } }); btNext.setOnAction(e -> { try { long currentPosition = raf.getFilePointer(); if (currentPosition < raf.length()) readAddress(currentPosition); } catch (IOException ex) { } }); btPrevious.setOnAction(e -> { try { long currentPosition = raf.getFilePointer(); if (currentPosition - 2 * RECORD_SIZE > 0) // Why 2 * 2 * RECORD_SIZE? See the follow-up remarks readAddress(currentPosition - 2 * 2 * RECORD_SIZE); else readAddress(0); } catch (IOException ex) { } }); btLast.setOnAction(e -> { try { long lastPosition = raf.length(); if (lastPosition > 0) // Why 2 * RECORD_SIZE? See the follow-up remarks readAddress(lastPosition - 2 * RECORD_SIZE); } catch (IOException ex) { } }); btUpdate.setOnAction(e -> { try { writeAddress(raf.getFilePointer() - 2 * RECORD_SIZE); } catch (IOException ex) { } }); } /** Write a record at the end of the file */ public void writeAddress(long position) { try { raf.seek(position); FixedLengthStringIO.writeFixedLengthString( tfName.getText(), NAME_SIZE, raf); FixedLengthStringIO.writeFixedLengthString( tfStreet.getText(), STREET_SIZE, raf); FixedLengthStringIO.writeFixedLengthString( tfCity.getText(), CITY_SIZE, raf); FixedLengthStringIO.writeFixedLengthString( tfState.getText(), STATE_SIZE, raf); FixedLengthStringIO.writeFixedLengthString( tfZip.getText(), ZIP_SIZE, raf); } catch (IOException ex) { ex.printStackTrace(); } } /** Read a record at the specified position */ public void readAddress(long position) throws IOException { raf.seek(position); String name = FixedLengthStringIO.readFixedLengthString( NAME_SIZE, raf); String street = FixedLengthStringIO.readFixedLengthString( STREET_SIZE, raf); String city = FixedLengthStringIO.readFixedLengthString( CITY_SIZE, raf); String state = FixedLengthStringIO.readFixedLengthString( STATE_SIZE, raf); String zip = FixedLengthStringIO.readFixedLengthString( ZIP_SIZE, raf); tfName.setText(name); tfStreet.setText(street); tfCity.setText(city); tfState.setText(state); tfZip.setText(zip); } /** * 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); } } class FixedLengthStringIO { /** Read fixed number of characters from a DataInput stream */ public static String readFixedLengthString(int size, DataInput in) throws IOException { // Declare an array of characters char[] chars = new char[size]; // Read fixed number of characters to the array for (int i = 0; i < size; i++) chars[i] = in.readChar(); return new String(chars); } /** Write fixed number of characters to a DataOutput stream */ public static void writeFixedLengthString(String s, int size, DataOutput out) throws IOException { char[] chars = new char[size]; // Fill in string with characters s.getChars(0, s.length(), chars, 0); // Fill in blank characters in the rest of the array for (int i = Math.min(s.length(), size); i < chars.length; i++) chars[i] = ' '; // Create and write a new string padded with blank characters out.writeChars(new String(chars)); } }