这是我目前的输出：
********MENU********
1. UNIT
2. EXIT
*********************
Select your option from 1 or 2: 1
********MENU********
1. VIEW LIST
2. BACK TO MAIN
*********************
Select your option from 1 or 2: 1
This are the list of the units:
[1] Asero/California
[2] Captain America/Pennsylvania
What unit do you want to modify? 1
Asero/California
Asero/California
Unit Name: Iron Man
Unit Location: California
Return to menu? Select 1: 1
********MENU********
1. VIEW LIST
2. BACK TO MAIN
*********************
Select your option from 1 or 2: 1
This are the list of the units:
[1] Asero/California
[2] Captain America/Pennsylvania
What unit do you want to modify?
Process interrupted by user.
我想要的是“Asero / California”被修改并替换为“Iron Man / California”。
原始输出仍为：
[1] Asero/California
[2] Captain America/Pennsylvania
我想要的输出是当我修改它现在应该是的数据时：
[1] Iron Man/California
[2] Captain America/Pennsylvania
我有一个textfile =“practice.txt”，这是存储数据的地方。
我还有另一个文本文件=“tempPractice.txt”，它仅用于放置临时数据。
public class Practice
{
List<String> lines = new ArrayList<String>();
public Practice()
{
try
{
String line = "";
System.out.println("********MENU********");
System.out.println("1. UNIT");
System.out.println("2. EXIT");
System.out.println("*********************");
System.out.print("Select your option from 1 or 2: ");
Scanner sc = new Scanner(System.in);
line = sc.next();
if(line.equals("1"))
{
unitMenu();
}
else if(line.equals("2"))
{
System.exit(0);
}
else
{
System.out.println("Incorrect code, please select from 1 or 2.");
new Practice();
}
}
catch(Exception e)
{
e.printStackTrace();
}
}
public void unitMenu()
{
try
{
String line = "";
System.out.println("********MENU********");
System.out.println("1. VIEW LIST");
System.out.println("2. BACK TO MAIN");
System.out.println("*********************");
System.out.print("Select your option from 1 or 2: ");
Scanner sc = new Scanner(System.in);
line = sc.next();
if(line.equals("1"))
{
updateData();
}
else if(line.equals("2"))
{
new Practice();
}
else
{
System.out.println("Incorrect code, please select from 1 or 2.");
unitMenu();
}
}
catch(Exception e)
{
e.printStackTrace();
}
}
public void updateData()
{
lines = new ArrayList<String>();
File f = new File("practice.txt");
BufferedReader bR, bR2;
BufferedWriter bW;
Scanner sc, sc2;
String str = "", scanLine, oldFile, newFile, tmpFile, uName, uLoc;
int numLine;
try
{
if(!f.exists())
{
System.out.println("File not found!");
}
else
{
bR = new BufferedReader(new FileReader("practice.txt"));
while((str = bR.readLine()) != null)
{
lines.add(str);
}
System.out.println();
System.out.println("This are the list of the units:");
for(int i=0,j=1;i<lines.size();i++,j++)
{
System.out.println( "[" + j + "] " + lines.get(i).toString());
}
System.out.print("What unit do you want to modify? ");
sc = new Scanner(System.in);
numLine = sc.nextInt();
int count = numLine;
--count;
for(int k=0;k<lines.size();k++)
{
if(count == k)
{
System.out.println(lines.get(k).toString());
//used for checking to know what data it returns
oldFile = lines.get(count).toString();
System.out.println(oldFile);
//method to replace a data --> not working/trial and error?
bW = new BufferedWriter(new FileWriter("tmpPractice.txt"));
System.out.print("Unit Name: ");
sc = new Scanner(System.in);
uName = sc.nextLine();
bW.write(uName);
bW.append('/');
System.out.print("Unit Location: ");
sc2 = new Scanner(System.in);
uLoc = sc2.nextLine();
bW.write(uLoc);
bW.newLine();
bW.close();
System.out.print("Return to menu? Select 1: ");
sc = new Scanner(System.in);
scanLine = sc.next();
if(scanLine.equals("1"))
{
unitMenu();
}
else
{
System.out.println("Error. Select only 1.");
updateData();
}
bR2 = new BufferedReader(new FileReader("tmpPractice.txt"));
while((newFile = bR2.readLine()) != null)
{
tmpFile = newFile;
oldFile = tmpFile;
bW = new BufferedWriter(new FileWriter("practice.txt", true));
bW.write(oldFile);
bW.close();
}
System.out.println(oldFile);
bR2.close();
}
bR.close();
}
}
}
catch(Exception e)
{
e.printStackTrace();
}
}
public static void main(String[] a)
{
new Practice();
}
}
我该怎么办？我应该怎么做或者我应该在我的代码中使用什么？ 有没有更简单的方法来做到这一点？任何反馈/建议/评论/帮助都将深受赞赏。
我还是Java新手，我正在为自己做很多练习，我达到了可以将数据附加到IO文件的程度，但是，我仍然不知道如何修改/替换文件中的特定数据而不删除其所有内容。
请帮助我，我真的想了解更多。
答案 0 :(得分：1)
看看这个并相应地修改。
public static void replaceSelected(String address) {
try {
String x = "t";
System.out.println("started searching for line");
File inputFile1 = new File(old file where line is to be updated);
File tempFile = new File(address+"/myTempFile.txt");
BufferedReader reader = new BufferedReader(new FileReader(old file "));
String lineToRemove = "add line to remove as a variable or a text";
String currentLine;
while((currentLine = reader.readLine()) != null) {
// trim newline when comparing with lineToRemove
String trimmedLine = currentLine.trim();
if(trimmedLine.equals(lineToRemove) && x.contentEquals("t")) {
x ="f";
} else if(trimmedLine.equals(lineToRemove) && x.contentEquals("f")) {
System.out.println("removed desired header");
System.out.println("Line"+trimmedLine);
continue;
}
FileWriter fw = new FileWriter(new file address,true);
BufferedWriter bw = new BufferedWriter(fw);
bw.write(currentLine);
System.out.println(currentLine);
bw.write("\n");
bw.close();
}
// writer.close();
reader.close();
boolean success3 = (new File (old file address)).delete();
if (success3) {
System.out.println(" Xtra File deleted");
}
} catch (Exception e){
}
答案 1 :(得分：1)
我已经制定了这段代码。在我的代码中，我没有使用临时文件而是使用 arraylist 来将旧值替换为新值。之后我将arraylist写下来文件。请参阅下面的更改代码。我这里只包含了更改过的代码。这对我来说很有用。
for(int k=0;k<lines.size();k++)
{
if(count == k)
{
System.out.println(lines.get(k).toString());
//used for checking to know what data it returns
oldFile = lines.get(count).toString();
System.out.println(oldFile);
System.out.print("Unit Name: ");
sc = new Scanner(System.in);
uName = sc.nextLine();
System.out.print("Unit Location: ");
sc2 = new Scanner(System.in);
uLoc = sc2.nextLine();
String replaceString = uName+"/"+uLoc;
lines.set(k, replaceString);
FileOutputStream fop = null;
fop = new FileOutputStream(f);
for(String content:lines){
byte[] contentInBytes = content.getBytes();
fop.write(contentInBytes);
fop.write("\n".getBytes());
}
fop.flush();
fop.close();
System.out.print("Return to menu? Select 1: ");
sc = new Scanner(System.in);
scanLine = sc.next();
if(scanLine.equals("1"))
{
unitMenu();
}
else
{
System.out.println("Error. Select only 1.");
updateData();
}
}
bR.close();
}
你用String replaceString = ...？ replaceString是值还是变量？
replaceString是一个包含用户输入值的变量 替换文件中所需的字符串值
另一个是：lines.set（k，replaceString） - ＆gt;我还可以将此声明为public void replaceString ???或者这是更简单的方法？
这里我们正在替换arraylist中的索引（k）值（行） 包含输入文件值，用户输入值。
另外，请问，byte []的用途是什么，是charAt []还是更像Tokenizer？
现在替换的内容正在写回文件。为此，我们是 将字符串值转换为字节数组（byte []）并写入 使用FileOutputStream