I have a super beginner's question. I have a computer science test today and one of the practice problems is this:
This is the code I have for it so far:
import java.util.*;
import java.io.*;
public class ReadFile
{
public static void main(String[] args) throws FileNotFoundException
{
PrintWriter out = new PrintWriter("hello.txt");
out.println("Hello, World");
File readFile = new File("hello.txt");
Scanner in = new Scanner(readFile);
ArrayList<String> x = new ArrayList<String>();
int y = 0;
while (in.hasNext())
{
x.add(in.next());
y++;
}
if (x.size() == 0)
{
System.out.println("Empty.");
}
else
{
System.out.println(x.get(y));
}
in.close();
out.close();
}
}
What's wrong with this code?
1) You need to close the stream
2) You need to refer to the x Arraylist with (y-1) otherwise you will get a java.lang.IndexOutOfBoundsException
. The indexes starts from 0 and not from 1.
http://www.tutorialspoint.com/java/util/arraylist_get.htm
public static void main(String[] args) throws FileNotFoundException
{
PrintWriter out = new PrintWriter("hello.txt");
out.println("Hello, World");
out.close();
File readFile = new File("hello.txt");
Scanner in = new Scanner(readFile);
ArrayList<String> x = new ArrayList<String>();
int y = 0;
while (in.hasNext())
{
x.add(in.next());
y++;
}
in.close();
if (x.size() == 0)
{
System.out.println("Empty.");
}
else
{
System.out.println(x.get(y-1));
}
}
}
I guess what's wrong with the code ist that you cant read anything from the file.
this is because PrintWriter is buffered
fileName - The name of the file to use as the destination of this writer. If the file exists then it will be truncated to zero size; otherwise, a new file will be created. The output will be written to the file and is buffered .
You need to close the file you have just writen to before openning it for reading so that the changes are fluched to the physical storage. Thus moving out.close();
right after out.println("Hello, World");
class FileWritingDemo {
public static void main(String [] args) {
char[] in = new char[13]; // to store input
int size = 0;
try {
File file = new File("MyFile.txt"); // just an object
FileWriter fw = new FileWriter(file); // create an actual file & a FileWriter obj
fw.write("Hello, World!"); // write characters to the file
fw.flush(); // flush before closing
fw.close(); // close file when done
FileReader fr = new FileReader(file); // create a FileReader object
size = fr.read(in); // read the whole file!
for(char c : in) // print the array
System.out.print(c);
fr.close(); // again, always close
} catch(IOException e) { }
}
}
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