我正在尝试在eclipse中执行文件I / O.这是代码：
import java.io.FileInputStream;
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
import java.util.StringTokenizer;
public class TextDB {
public static final String SEPARATOR = "|";
// an example of reading
public static ArrayList readProfessors(String filename) throws IOException {
// read String from text file
ArrayList stringArray = (ArrayList) read(filename);
ArrayList alr = new ArrayList();// to store Professors data
for (int i = 0; i < stringArray.size(); i++) {
String st = (String) stringArray.get(i);
// get individual 'fields' of the string separated by SEPARATOR
StringTokenizer star = new StringTokenizer(st, SEPARATOR); // pass in the string to the string tokenizer using delimiter ","
String name = star.nextToken().trim(); // first token
String email = star.nextToken().trim(); // second token
int contact = Integer.parseInt(star.nextToken().trim()); // third token
// create Professor object from file data
Professor prof = new Professor(name, email, contact);
// add to Professors list
alr.add(prof);
}
return alr;
}
// an example of saving
public static void saveProfessors(String filename, List al) throws IOException {
List alw = new ArrayList();// to store Professors data
for (int i = 0; i < al.size(); i++) {
Professor prof = (Professor) al.get(i);
StringBuilder st = new StringBuilder();
st.append(prof.getName().trim());
st.append(SEPARATOR);
st.append(prof.getEmail().trim());
st.append(SEPARATOR);
st.append(prof.getContact());
alw.add(st.toString());
}
write(filename, alw);
}
/**
* Write fixed content to the given file.
*/
public static void write(String fileName, List data) throws IOException {
PrintWriter out = new PrintWriter(new FileWriter(fileName));
try {
for (int i = 0; i < data.size(); i++) {
out.println((String) data.get(i));
}
} finally {
out.close();
}
}
/**
* Read the contents of the given file.
*/
public static List read(String fileName) throws IOException {
List data = new ArrayList();
Scanner scanner = new Scanner(new FileInputStream(fileName));
try {
while (scanner.hasNextLine()) {
data.add(scanner.nextLine());
}
} finally {
scanner.close();
}
return data;
}
public static void main(String[] aArgs) {
TextDB txtDB = new TextDB();
String filename = "professor.txt";
try {
// read file containing Professor records.
ArrayList al = TextDB.readProfessors(filename);
for (int i = 0; i < al.size(); i++) {
Professor prof = (Professor) al.get(i);
System.out.println("Name " + prof.getName());
System.out.println("Contact " + prof.getContact());
}
Professor p1 = new Professor("Joseph", "jos@ntu.edu.sg", 67909999);
// al is an array list containing Professor objs
al.add(p1);
// write Professor record/s to file.
TextDB.saveProfessors(filename, al);
} catch (IOException e) {
System.out.println("IOException > " + e.getMessage());
}
}
}
我的教授班：
import java.io.Serializable;
public class Professor implements Serializable {
private String name;
private String email;
private int contact;
public Professor(String n, String e, int c) {
name = n;
email = e;
contact = c;
}
public String getName() {
return name;
}
public int getContact() {
return contact;
}
public String getEmail() {
return email;
}
public boolean equals(Object o) {
if (o instanceof Professor) {
Professor p = (Professor) o;
return (getName().equals(p.getName()));
}
return false;
}
}
然而，当我运行它时，编译器告诉指定的文件＆＃34; professor.txt＆＃34;找不到。我以为编译器会根据这些代码自动创建文本文件吗？
提前致谢。
答案 0 :(得分：0)
在你的主要文件中，你首先阅读文件，然后编写它：如果文件不存在，它会抛出异常。也许，第一次运行它时，文件就存在了（也许你已经编写了代码来编写文件，然后你就启动它了。）
所以，两个解决方案......
首先：改变你的主要顺序。
def add_or_update_score(name, class_group, score):
with lite.connect('results.db') as conn:
# Create the table, if doesn't exist yet
conn.execute('CREATE TABLE IF NOT EXISTS scores (name TEXT, class_group INTEGER, score INTEGER)')
# Check if a record already exists
if list(conn.execute('SELECT * FROM scores where name = ?', (name,))):
# A record already exists
conn.execute('UPDATE scores SET score = ? WHERE (name = ? AND class_group = ?)', (score, name, class_group))
else:
# No record exists
conn.execute('INSERT INTO scores VALUES (?, ?, ?)', (name, class_group, score))
第二步：检查文件是否存在，如果不存在则跳过读取
public static void main(String[] aArgs) {
TextDB txtDB = new TextDB();
String filename = "professor.txt";
try {
Professor p1 = new Professor("Joseph", "jos@ntu.edu.sg", 67909999);
// al is an array list containing Professor objs
al.add(p1);
// write Professor record/s to file.
TextDB.saveProfessors(filename, al);
// read file containing Professor records.
ArrayList al = TextDB.readProfessors(filename);
for (int i = 0; i < al.size(); i++) {
Professor prof = (Professor) al.get(i);
System.out.println("Name " + prof.getName());
System.out.println("Contact " + prof.getContact());
}
} catch (IOException e) {
System.out.println("IOException > " + e.getMessage());
}
}
评论后更新：
public static void main(String[] aArgs) {
TextDB txtDB = new TextDB();
String filename = "professor.txt";
try {
//check if the file exist
File oFile = new File(filename);
if(oFile.exist()) {
// read file containing Professor records.
ArrayList al = TextDB.readProfessors(filename);
for (int i = 0; i < al.size(); i++) {
Professor prof = (Professor) al.get(i);
System.out.println("Name " + prof.getName());
System.out.println("Contact " + prof.getContact());
}
}
Professor p1 = new Professor("Joseph", "jos@ntu.edu.sg", 67909999);
// al is an array list containing Professor objs
al.add(p1);
// write Professor record/s to file.
TextDB.saveProfessors(filename, al);
} catch (IOException e) {
System.out.println("IOException > " + e.getMessage());
}
}
答案 1 :(得分：0)
在尝试阅读应用程序中的文件之前，如果它不存在，请直接创建：
String filename = "professor.txt" ;
File file = new File(fileName);
if(!file.exists()){
file.createNewFile();
}
或致电您的write方法。
String filename = "professor.txt" ;
File file = new File(fileName);
if(!file.exists()){
TextDB.saveProfessors(filename, new ArrayList());
}
PrintWriter将为您创建文件，即使没有写入任何内容（例如此空列表）。