内容发布更新时间 : 2024/5/22 16:28:06星期一 下面是文章的全部内容请认真阅读。

// Buttons

private Button btAdd = new Button(\); private Button btFirst = new Button(\); private Button btNext = new Button(\);

private Button btPrevious = new Button(\); private Button btLast = new Button(\); private Button btUpdate = new Button(\);

public Exercise17_09() {

// Open or create a random access file try {

raf = new RandomAccessFile(\, \); }

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(\), 0, 0); p1.add(new Label(\), 0, 1); p1.add(new Label(\), 0, 2); p1.add(tfName, 1, 0); p1.add(tfStreet, 1, 1);

HBox p2 = new HBox(5);

p2.getChildren().addAll(tfCity, new Label(\), tfState, new Label(\), 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(\); // 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)); } }

17.10

import java.io.*;

public class Exercise17_10 {

public static void main(String[] args) throws Exception { // Check usage

if (args.length != 2) {

System.out.println(\numberOfPieces\); System.exit(1); }