如何在Java中阅读某一行&后面几行
编辑：好的，我正在寻找一个特定的行，然后在找到的行之后打印几行。这就是我现在所拥有的，但是得到了很多错误，大多数都没有建立FileNotFoundException，但是它在那里，所以我不知道发生了什么，一个错误说我需要一个；在“for”循环中。请帮忙如何在Java中阅读某一行&后面几行,java,Java,编辑：好的，我正在寻找一个特定的行，然后在找到的行之后打印几行。这就是我现在所拥有的，但是得到了很多错误，大多数都没有建立FileNotFoundException，但是它在那里，所以我不知道发生了什么，一个错误说我需要一个；在“for”循环中。请帮忙 import java.io.BufferedReader; import java.io.FileReader; import java.io.FileNotFoundException; public class Animals { St
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.FileNotFoundException;
public class Animals {
String line;
int i = 0;
BufferedReader animals = new BufferedReader(new FileReader
("//Documents//animals.txt"));
string animalChoices () {
string animalChoice = while ((line = animals.readLine()) != null)) {
for (i = 0, i < 4, i++) {
System.out.print(line);
}
}
}
string displayAnimals () {
string displayAnimal = while ((line = animals.readLine()) != null) {
for (i=0, i<4, i++) {
if (line.contains("*****")) {
string alertLine = line.replace("*****", "ALERT!!! ");
system.out.println(alertLine);
}
else if {
system.out.println(line);
}
}
}
}
}
marmaset - rick
detail 1
detail 2
detail 3
ALERT: detail 4
看看这是否适合你 我创建了一个包含以下内容的文件：
This is a line 123
This is a line 456
This is a line 789
This is a line 012
This is a line 345
This is a line 678
This is a line 901
This is a line 234
This is a line 567
package stackoverflow;
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
public class CustomFileReader {
/**
* Grab a line from a file containing a pattern, and a number of "non-zero"
* lines after it. Return array of Strings as the result.
* @param file File to search
* @param containsThis text string first line must have...
* @param linesToGrab # of lines to grab total.
* @return null if file doesn't exist or the string pattern wasn't found.
*/
public static String[] getLines(File file, String containsThis,int linesToGrab)
{
if(!file.exists()){
System.err.println("File doesn't exist...");
return null;
}
int linesGrabbed = 0;
String[] result = new String[linesToGrab];
boolean lookingForPattern = true;
try {
BufferedReader br = new BufferedReader(new FileReader(file));
for(String line; (line = br.readLine()) != null; )
{
if(lookingForPattern){
if(line.contains(containsThis)){
result[linesGrabbed++] = line;
lookingForPattern = false;
}
}
else{
/** Got the pattern, now just grab lines that are "non-zero". */
if(line.length() > 0){
result[linesGrabbed++] = line;
if(linesGrabbed >= linesToGrab){
br.close();
return result;
}
}
}
}
} catch (Exception e) {
System.err.println(e.toString());
}
return result;
}
}
public static void main(String[] args) {
String[] result = CustomFileReader.getLines(
new File("c:/stackoverflow/myFile.txt"), "012", 5);
if(result != null){
for(String line : result){
System.out.println(line);
}
}
}
This is a line 012
This is a line 345
This is a line 678
This is a line 901
This is a line 234
Some random line
Another ramdom line
*****
lion
tiger
bear
cow
pig
chicken
panda
package stackoverflow;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.List;
public class Animals
{
/**
* Based on your code, I'm guessing this method is meant to read all
* lines of a file containing a list of animals and return all the lines
* read from the file to whoever called this method...
* I used a List instead of an array since you don't have to know how
* many lines are in the file ahead of time (you'd need to initialize an
* array, not a List.) I'll demonstrate how to access the List of
* Strings in the example.
* @param filename pathname of the file. Ex. "c:/stackoverflow/myFile.txt"
* or "c:\\stackoverflow\\myFile.txt"
* @return List of Strings read from the file.
*/
public static List<String> animalChoices (String filename)
{
List<String> animalChoiceList = new ArrayList<>();
BufferedReader animals;
try {
animals = new BufferedReader(new FileReader(filename));
} catch (FileNotFoundException ex) {
System.err.println(ex.toString());
/* list returned with no entries. */
return animalChoiceList;
}
try {
String line;
while ((line = animals.readLine()) != null)
{
animalChoiceList.add(line);
}
animals.close();
} catch (Exception e) {
System.err.println(e.toString());
}
return animalChoiceList;
}
/**
* Search a provided filename for a certain character string, add that
* line to a String array, replace it with "ALERT!!! ", then add the
* next (linesToGrab - 1) lines and add those to the array. Skip
* blank lines.
* @param filename file path in String format "c:/folder/filename.txt"
* @param searchCriteria ex. "*****" or "lion" or "1234"
* @param linesToGrab total number of lines to grab
* @return String array with the results. null if file not there.
*/
public static String[] displayAnimals(String filename,
String searchCriteria, int linesToGrab)
{
/* initialize the array to linesToGet long. */
String[] result = new String[linesToGrab];
BufferedReader animals;
try {
animals = new BufferedReader(new FileReader(filename));
} catch (FileNotFoundException ex) {
System.err.println(ex.toString());
/* return null if a reader could not be opened */
return null;
}
int linesGrabbed = 0;
boolean lookingForPattern = true;
try {
for(String line; (line = animals.readLine()) != null; )
{
if(lookingForPattern){
if(line.contains(searchCriteria)){
result[linesGrabbed++] =
line.replace(searchCriteria, "ALERT!!! ");
lookingForPattern = false;
}
}
else{
/** Got the pattern, now just grab lines that are "non-zero". */
if(line.length() > 0){
result[linesGrabbed++] = line;
if(linesGrabbed >= linesToGrab){
animals.close();
return result;
}
}
}
}
} catch (Exception e) {
System.err.println(e.toString());
}
return result;
}
}
你们已经学会如何使用扫描器了吗？是的，这次我附加了一些代码。为什么所有的东西都是小写的？你知道的。Java区分大小写，2。Java类都以大写字母开头，例如String、System。3.字符串displayAnimal=while。。。这是错误的。请看一下如何进行正确的变量赋值和循环。更好。但对于文件路径，请始终使用绝对路径文件路径来驱动字母，直到其他所有操作都正常为止。相对路径从正在运行的.class文件开始。您应该只使用单斜杠。你可能想逃避他们，但那是用反斜杠完成的\\。您的正确路径应该类似于C:/Users//Documents/animals.txt是否有一种基于用户输入运行此操作的方法？例如，如果我们想在您的案例中查找数字，它的运行方式与您所展示的相同，或者如果我们想查找字母，那么假设所发布的数字是字母的各个字母，而数字是以字符串的形式呈现的，因此，您可以用e 0替换012，它会找到相同的行。关于最初尝试中的一些语法，我建议您尝试使用诸如NetBeans IDE之类的程序。您的错误将以红色突出显示，指出您需要更改的内容，例如字符串条目。因此，对于每只动物，都有一个四行的列表，下面有详细信息。这是统一的，我将编辑问题以更好地显示它。抱歉。我一直很好奇，是否有可能在选定的一行之后阅读n行。******用于应显示的警报。
package stackoverflow;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.List;
public class Animals
{
/**
* Based on your code, I'm guessing this method is meant to read all
* lines of a file containing a list of animals and return all the lines
* read from the file to whoever called this method...
* I used a List instead of an array since you don't have to know how
* many lines are in the file ahead of time (you'd need to initialize an
* array, not a List.) I'll demonstrate how to access the List of
* Strings in the example.
* @param filename pathname of the file. Ex. "c:/stackoverflow/myFile.txt"
* or "c:\\stackoverflow\\myFile.txt"
* @return List of Strings read from the file.
*/
public static List<String> animalChoices (String filename)
{
List<String> animalChoiceList = new ArrayList<>();
BufferedReader animals;
try {
animals = new BufferedReader(new FileReader(filename));
} catch (FileNotFoundException ex) {
System.err.println(ex.toString());
/* list returned with no entries. */
return animalChoiceList;
}
try {
String line;
while ((line = animals.readLine()) != null)
{
animalChoiceList.add(line);
}
animals.close();
} catch (Exception e) {
System.err.println(e.toString());
}
return animalChoiceList;
}
/**
* Search a provided filename for a certain character string, add that
* line to a String array, replace it with "ALERT!!! ", then add the
* next (linesToGrab - 1) lines and add those to the array. Skip
* blank lines.
* @param filename file path in String format "c:/folder/filename.txt"
* @param searchCriteria ex. "*****" or "lion" or "1234"
* @param linesToGrab total number of lines to grab
* @return String array with the results. null if file not there.
*/
public static String[] displayAnimals(String filename,
String searchCriteria, int linesToGrab)
{
/* initialize the array to linesToGet long. */
String[] result = new String[linesToGrab];
BufferedReader animals;
try {
animals = new BufferedReader(new FileReader(filename));
} catch (FileNotFoundException ex) {
System.err.println(ex.toString());
/* return null if a reader could not be opened */
return null;
}
int linesGrabbed = 0;
boolean lookingForPattern = true;
try {
for(String line; (line = animals.readLine()) != null; )
{
if(lookingForPattern){
if(line.contains(searchCriteria)){
result[linesGrabbed++] =
line.replace(searchCriteria, "ALERT!!! ");
lookingForPattern = false;
}
}
else{
/** Got the pattern, now just grab lines that are "non-zero". */
if(line.length() > 0){
result[linesGrabbed++] = line;
if(linesGrabbed >= linesToGrab){
animals.close();
return result;
}
}
}
}
} catch (Exception e) {
System.err.println(e.toString());
}
return result;
}
}
package stackoverflow;
import java.util.List;
public class StackOverflow {
/**
* @param args the command line arguments
*/
public static void main(String[] args) {
String filename = "c:/stackoverflow/animalFile.txt";
List<String> animals = Animals.animalChoices(filename);
System.out.println("All lines in the file:");
for(String animal : animals){
System.out.println(animal);
}
int linesToGet = 5;
String searchCriteria = "*****";
String[] result =
Animals.displayAnimals(filename, searchCriteria, linesToGet);
System.out.println("\n\nOnly lines after the search criteria");
for(String line : result){
System.out.println(line);
}
}
}
All lines in the file:
Some random line
Another ramdom line
*****
lion
tiger
bear
cow
pig
chicken
panda
Only lines after the search criteria
ALERT!!!
lion
tiger
bear
cow