This question already has answers here:
Closed 10 years ago.
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Causes of 'java.lang.NoSuchMethodError: main Exception in thread “main”'
I am trying to write a byte array in a text file. It is giving me error:
java.lang.NoSuchMethodError: main
Exception in thread "main"
The code i am using is as under
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.io.IOException;
import java.io.Writer;
public class writefile {
//it works well
public static void main()throws IOException{
Writer output = null;
byte[] a= {1,2,3,4,5,6};
try {
String text = "abcd...\n";
String str3 = text.concat("the end");
String NL = System.getProperty("line.separator");
str3 = str3.concat(NL);
str3= str3.concat("next line");
for ( int i=0; i < a.length; i++){
str3 = str3.concat(NL);
str3= str3.concat(" " +a[i]);
}
File file = new File("write.txt");
output = new BufferedWriter(new FileWriter(file));
output.write(str3);
System.out.println("Your file has been written");
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
if (output != null) {
output.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
Kindly help how can i resolve the problem.
The main method of a Java program must take an argument of type String[] representing the arguments (if any) passed to the program on launch.
the main signature must contain String[] argument
Related
I made the program in java to convert the text in the file in the uppercase but it erases data instead of converting it
But when I take data from 1 file and write converted data into another file, it works fine.
So I got problem that how can I do this using single file.
Here below is my code, Tell me how to correct this?
import java.io.FileReader;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.FileWriter;
public class uppercase{
public static void main(String[] args) {
try {
FileReader reader = new FileReader("e.txt");
FileWriter writer = new FileWriter("e.txt");
int data;
int data2;
while((data=reader.read())!= -1) {
data2=Character.toUpperCase(data);
writer.write(data2);
}
reader.close();
writer.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}
this is bad idea, because you are writing to same file you are reading from. You should either:
Load complete file to memory, close it and then dump it to same file.
Save to different file and rename (better)
firstly you open a stream to read from file and append the result to a String variable and at the end of reading, you write all the data to the file:
try {
FileReader reader = new FileReader("e.txt");
String result = "";
int data;
int data2;
while ((data = reader.read()) != -1) {
data2 = Character.toUpperCase(data);
result += (char)data2;
}
reader.close();
System.out.println(result);
FileWriter writer = new FileWriter("e.txt");
writer.write(result);
writer.flush();
writer.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 5 years ago.
i´ve been trying to read the lines of this file to save them into an array afterwards, but when I try to print the lines to try it out it has a nullpointer on the line of :
while( (line = br.readLine()) !=null
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
public class Main1 {
public static void main(String[] args) {
// TODO Auto-generated method stub
String line;
BufferedReader br = null ;
try {
new BufferedReader(new FileReader("/Users/Daniq/Desktop/eda/pruebaEda.txt"));
System.out.println("Done");
try {
while( (line = br.readLine()) != null){
System.out.println(line);
}
} catch (IOException e) {
// TODO Auto-generated catch block
System.out.println("error ");
}
} catch(FileNotFoundException fnfex){
System.out.println("File not found");
}
}
}
You dont initalize br reference, after try,
br = new BufferedReader...
I don't know if it is possible or not, but my requirement is like - I have to read data from a file called System.evtx in my java program.
While I am doing this like simple file reading I am getting some ASCII character or I can say un-readable format.
Is there any way to solve this issues.
Thanks in advance.
This is a difficult question to answer without an example of the file content, but after some googling it seems to be a windows event log file? So im unsure about the exact format but apparently they can be converted to .csv files using powershell:
Get-WinEvent -Path c:\path\to\eventlog.evtx |Export-Csv eventlog.csv
Once its in a csv format you could simple parse them in the traditional way of csv or just split by comma's etc.
import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
public class CSVReader {
public static void main(String[] args) {
String csvFile = "eventlog.csv";
BufferedReader br = null;
String line = "";
String cvsSplitBy = ",";
try {
br = new BufferedReader(new FileReader(csvFile));
while ((line = br.readLine()) != null) {
// use comma as separator
String[] line = line.split(cvsSplitBy);
for(int i=0;i<line.length;i++){
System.out.println(line[i]);
}
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (br != null) {
try {
br.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
}
I have this code below. Basically I'm getting an input from a given url. This website shows a sentence. Each time I reload the website it gets a new sentence and so on. So, I managed to get that working. Now I'm trying to write the sentence in a textfile. But something is wrong. It only writes the first line and nothing else. What's wrong with my code?
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLConnection;
public class ReadIp {
public static void main(String[] args) throws MalformedURLException, IOException,
InterruptedException {
ReadIp readIP = new ReadIp();
while (true) {
readIP.getIP();
Thread.sleep(2000);
}
}
BufferedReader buff;
InputStreamReader inStream;
String line;
URL url;
URLConnection urlConn;
FileWriter fileWriter ;
BufferedWriter bufferedWriter;
public ReadIp() throws IOException {
fileWriter = new FileWriter("myfile.txt", true);
bufferedWriter = new BufferedWriter(fileWriter);
}
public void getIP() throws MalformedURLException, IOException {
this.url = new URL("http://test.myrywebsite.co.uk");
this.urlConn = this.url.openConnection();
this.inStream = new InputStreamReader(this.urlConn.getInputStream());
this.buff = new BufferedReader(this.inStream);
try {
while ((this.line = this.buff.readLine()) != null)
{
System.out.println(this.line);
try {
this.bufferedWriter.write(this.line);
this.bufferedWriter.write("\n");
this.bufferedWriter.flush();
} catch (IOException e)
{
}
}
if (this.bufferedWriter != null)
{
this.bufferedWriter.close();
}
this.inStream.close();
}
catch (Exception ex)
{
}
}
}
Any help would be greatly appreciated.
Thank you.
Move the statement
writer.close();
out of the inner try catch block so that you're not closing the OutputStream after writing the first entry to the file. The same applys to the InputStream
inStream.close();
The BufferedWriter is being opened in the constructor and is being closed in getIp. The constructor is called only once, but getIp is called every 2 seconds to read a sentence. So the BufferedWriter is being closed after the first line (and not opened again). The second call of getIp tries to write the second sentence but the BufferedWriter is closed. This should throw an Exception which is being ignored since the catch block is empty.
Never leave a catch block empty - as fgb wrote above!
First of all, at least add a printStackTrace() to each empty catch block, e.g.:
catch (Exception ex) {
ex.printStackTrace();
}
so you can see if an Exception is being thrown...
I would suggest to open the BufferedWriter in the method getIp instead of the constructor; or, if it should stay open all the time, close the BufferedWriter in an additional method, called after the loop in main terminates
How can I use a command line program from within Java?
I'm trying to pass a graph definition in the dot-language (see Wikipedia) to the interpreter program dot (see GraphViz) through java.
The problem is, that the program does not answer, after I have sent the dot-graph to its InputStream, because it does not know, that I'm finished sending the description.
This is, what I currently have:
package exercise4;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintStream;
import java.io.UnsupportedEncodingException;
public class Main {
public static void main(String[] args) {
PrintStream out = System.out;
BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
try {
final String start =
"strict graph LSR%1$d {\n" +
" node [shape=circle color=lightblue style=filled];\n\n" +
" {rank=same; A--B [label=6];}\n" +
" {rank=same; C--D [label=12]; D--E [label=4];}\n" +
" A--C [label=4]; B--D [label=4]; B--E [label=9];\n\n" +
" node [shape=record color=\"#000000FF\" fillcolor=\"#00000000\"];\n}\n";
Process dot = Runtime.getRuntime().exec("dot -Tsvg");
in = new BufferedReader(new InputStreamReader(System.in));
out = new PrintStream(dot.getOutputStream(), false, "UTF-8");
out.printf(start, 0);
out.flush();
out.close();
while(in.ready()) {
System.out.println(in.readLine());
}
in.close();
dot.destroy();
} catch (UnsupportedEncodingException ex) {
} catch (IOException ex) {
} finally {
out.close();
}
}
}
Looks as if you are reading from the wrong input stream. Have a look at this answer: https://stackoverflow.com/a/4741987/1686330