[英]java FileReader, Read text Line by Line
我有两节课。 首先,是TEXT类:在这里,我阅读了一个6行的文本文件。 我只想逐行阅读,但这可行。 但我想从第三行开始,也想从最后一行开始,我只希望以
这是文本文件代码。
<?xml version="1.0" encoding="iso-8859-1"?>
<ICONS ERROR="false" USERNAME="WAZ" FORMAT="FLAT" RECORDS="3">
<icon ID="55" NAM="A" />
<icon ID="87" NAM="B" />
<icon ID="53" NAM="C" />
</ICONS>
这是来自文件读取器的代码:
package packagechain;
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.util.Iterator;
import java.util.stream.Stream;
public class Text {
String fileName;
FileReader fr;
BufferedReader in;
Stream<String> lines;
Iterator<String> l;
boolean hasLine;
public Text() throws FileNotFoundException{
fileName = "E:/test30.xml";
fr = new FileReader(fileName);
in = new BufferedReader(fr);
lines = in.lines();
l = lines.iterator();
hasLine = true;
}
public String nextline() {
String nl;
if(l.hasNext()) {
nl = l.next();
//System.out.println(""+nl);
}
else {
System.out.println("No new line!");
hasLine = false;
nl=null;
}
return nl;
}
}
这是我可以在文本文件中编辑我想要的字符串的代码,我使用“ substring”,并且可以正常工作。 但是,如果到最后一行,在特定子字符串中没有任何值,就会出现错误...。
如果删除文本文件中的第1行和第2行以及第Alst行,则会发生错误:“线程“主”中的异常” java.lang.StringIndexOutOfBoundsException:字符串索引超出范围:java.lang.String.substring(String.java:1963 ),位于packagepackagechain.test4.main(test4.java:18)“
如果我在文本文件中添加第一行和第二行以及最后一行,则会出错。
错误:程序包packagechain.test4.main(test4.java:16)中的线程“ main”中的异常java.lang.NullPointerException
and here is the code:
package packagechain;
import java.io.FileNotFoundException;
public class test4 {
public static void main(String[] args) {
Text m;
String s;
try {
m = new Text();
while(m.hasLine) {
s = m.nextline();
String r = s.substring(10,12);
System.out.println(r);
}
} catch (FileNotFoundException e) {
System.out.println("File not found!");
}
}
}
您的Text类仅读取第一行,而您的主类正在为每次迭代实例化一个新的Text对象。 您的Text类可以使用方法行读取所有文件行,然后遍历它们并打印每一行。
package packagechain;
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.util.Iterator;
import java.util.stream.Stream;
public class Text {
String fileName;
FileReader fr;
BufferedReader in;
Stream<String> lines;
Iterator<String> l;
boolean hasLine;
public Text() throws FileNotFoundException{
fileName = "....4-line.txt";
fr = new FileReader(fileName);
in = new BufferedReader(fr);
lines = in.lines();
l = lines.iterator();
hasLine = true;
}
public String nexline() {
if(l.hasNext()) {
String nl = l.next();
System.out.println("Next line; "+nl);
return nl
}
else {
System.out.println("No new line!");
hasLine = false;
return null;
}
}
}
主班:
package packagechain;
public class MainProgram {
public static void main(String[] args) {
Text m;
String s;
try {
m = new Text();
while(m.hasLine) {
s = m.nexline();
//EXAMPLE: for each line, print a substring starting from its third character
if(s != null) System.out.println(s.substring(2));
//Here I edit in future these Line , so it's important that i get line by line from my other class, becaus I Have to edit each line itself!
}
} catch (FileNotFoundException e) {
System.out.println("File not found!");
}
}
}
在您的程序中,每个迭代文本类对象和缓冲区读取器对象都被重新分配,因此它们仅返回第一行
package packagechain;
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
public class Text {
public BufferedReader getBufferReader() {
BufferedReader in;
String fileName = "...4-line.txt";
FileReader fr = null;
try {
fr = new FileReader(fileName);
in = new BufferedReader(fr);
}
catch(FileNotFoundException fnfe){
System.out.println("Can't open");
}
catch(IOException ioe){
System.out.println("No new line!");
}
return in;
}
public void readLine(BufferedReader in){
try {
String line = in.readLine();
System.out.println("Next line; "+line);
catch(IOException ioe){
System.out.println("No new line!");
}
}
}
第二类代码是:
package packagechain;
public class MainProgram {
public static void main(String[] args) {
while(true){
Text m = new Text();
BufferedReader in=m.getBufferReader();
m.readLine(in);
//Here I edit in future these Line , so it's important that i get line by line from my other class, becaus I Have to edit each line itself!
}
}
}
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