Java:从文本文件中检索和删除随机行
我需要从txt文件中检索并删除随机行(同一行)。到目前为止,我已经提出了以下代码:Java:从文本文件中检索和删除随机行,java,io,Java,Io,我需要从txt文件中检索并删除随机行(同一行)。到目前为止,我已经提出了以下代码: public String returnAndDeleteRandomLine(String dir) throws FileNotFoundException, IOException { try (BufferedReader br = new BufferedReader(new FileReader(dir))) { //StringBuilder sb = new String
public String returnAndDeleteRandomLine(String dir) throws FileNotFoundException, IOException {
try (BufferedReader br = new BufferedReader(new FileReader(dir))) {
//StringBuilder sb = new StringBuilder();
//System.out.println("Value of line before while() " + line);
ArrayList fileContents = new ArrayList();
int maxLines = 0;
String line = br.readLine();
//System.out.println("Value of line before while() " + line);
while (line != null) {
fileContents.add(line.toString());
line = br.readLine();
//System.out.println("Value of line is: " + line);
}
System.out.println("Value of maxLines() " + maxLines);
Random rand = new Random();
int randomNumber = rand.nextInt(maxLines - 1) + 1;
System.out.println("Value of randomNumber: " + randomNumber);
int lineNumber = randomNumber;
if (fileContents.isEmpty()) {
return null;
} else System.out.println("Value of random line: " + fileContents.get(randomNumber).toString());
return fileContents.get(randomNumber).toString();
}
}
但我总是会犯不同的错误。最近的错误是:
线程“main”中maxLines()0异常的值
java.lang.IllegalArgumentException:绑定必须在
java.util.Random.nextInt(未知源代码)位于
TransmitToFile.returnAndDeleteRandomLine(TransmitToFile.java:247)位于
Main.Main(Main.java:98)
我甚至无法删除该行,因为我仍然无法检索该行。问题在于该行
int randomNumber = rand.nextInt(maxLines - 1) + 1;
如果
maxLines
为0
,则调用rand.nextInt(-1)
。因此,此参数必须为正的错误。您忘记了,因此将变量maxLines
的值设置为文件中的行数,并且由于其为0,因此会出现异常
您可以添加新方法以获得如下行号(如此答案所示:):
并将代码更改为:
int maxLines = 0;
致:
因此,
maxLines
变量将等于文件中的行数。错误在这一行:
int randomNumber = rand.nextInt(maxLines - 1) + 1;
您应该先添加一个复选框来检查尺寸:
int totalLines = maxLines - 1;
if(totalLines > 0) {
Random rand = new Random ();
int randomNumber = rand.nextInt (totalLines) + 1;
System.out.println("Value of randomNumber: " + randomNumber);
} else {
return null;
}
Random.nextInt(N)
提供0。。N-1
。由于所有指数都是从0开始计算的,而人类是从1开始计算的,所以出现了混淆
通用代码可以做得更简单:
public static String returnAndDeleteRandomLine(String dir) throws IOException {
Path path = Paths.get(dir);
List<String> lines = Files.readAllLines(path, StandardCharsets.UTF_8);
if (lines.isEmpty()) {
throw new IOException("Empty file: " + dir);
}
Random rand = new Random();
int lineIndex = rand.nextInt(lines.size()); // 0 .. lines.size() - 1
String line = lines.get(lineIndex);
System.out.printf("Line %d: %s%n", (lineIndex + 1), line);
lines.remove(lineIndex);
Files.write(path, lines, StandardCharsets.UTF_8,
StandardOpenOption.WRITE, StandardOpenOption.TRUNCATE_EXISTING);
return line;
}
publicstaticstringreturnanddeleterandomline(stringdir)抛出IOException{
Path=Path.get(dir);
列表行=Files.readAllLines(路径,StandardCharsets.UTF_8);
if(lines.isEmpty()){
抛出新IOException(“空文件:+dir”);
}
Random rand=新的Random();
int lineIndex=rand.nextInt(lines.size());//0..lines.size()-1
String line=lines.get(lineIndex);
System.out.printf(“第%d行:%s%n”,(lineIndex+1),第行);
行。删除(行索引);
写入(路径、行、标准字符集.UTF_8、,
StandardOpenOption.WRITE,StandardOpenOption.TRUNCATE_现有);
回流线;
}
如果文件为空(maxlines=0),此解决方案仍将失败,因此您还应检查(maxlines=0)是否返回;或者别的什么。在现实生活中可能不是什么大问题,但值得注意。
int totalLines = maxLines - 1;
if(totalLines > 0) {
Random rand = new Random ();
int randomNumber = rand.nextInt (totalLines) + 1;
System.out.println("Value of randomNumber: " + randomNumber);
} else {
return null;
}
public static String returnAndDeleteRandomLine(String dir) throws IOException {
Path path = Paths.get(dir);
List<String> lines = Files.readAllLines(path, StandardCharsets.UTF_8);
if (lines.isEmpty()) {
throw new IOException("Empty file: " + dir);
}
Random rand = new Random();
int lineIndex = rand.nextInt(lines.size()); // 0 .. lines.size() - 1
String line = lines.get(lineIndex);
System.out.printf("Line %d: %s%n", (lineIndex + 1), line);
lines.remove(lineIndex);
Files.write(path, lines, StandardCharsets.UTF_8,
StandardOpenOption.WRITE, StandardOpenOption.TRUNCATE_EXISTING);
return line;
}