K*B 1.5 book . PG 433 Error

[Deepak Jain]

There is a code in K&B that shows how to use FileWriter and FileReader to write and read the contents of a file.

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
 
public class FileTest1 {
 
/**
 * @param args
 */
public static void main(String[] args) {
File f = new File("file1.txt");
try {
FileWriter fw = new FileWriter(f);
fw.write("abc\ndef\n");
fw.flush();
fw.close();
} catch (IOException e) {
}
 
try {
FileReader fr = new FileReader(f);
char [] destBuf = new char[100];
System.out.println("destBuf.length:"+destBuf.length);
int size=fr.read(destBuf);
System.out.println("size:"+size);
System.out.println("FileContents");
for(char c :mrgreen: estBuf) {
System.out.print(c);
}
} catch (FileNotFoundException e) {
e.printStackTrace();
}catch (IOException e) {
e.printStackTrace();
}
}
}

The output :
abc
def
Boxes till the end....... [Square boxes]

As the read(char []dest) method reads the number of characters that is equal to the size of the declared array dest.
In the above program since of size of array is far greater than the length of the file , Using for(char c est) { } will iterate to the length of the array instead of the lenght of the file. Hence the above code should be modified to iterate the dest[] till the size returned by the read(). Hence the code should be modified as follows.

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
 
public class FileTest1 {
 
/**
 * @param args
 */
public static void main(String[] args) {
File f = new File("file1.txt");
try {
FileWriter fw = new FileWriter(f);
fw.write("abc\ndef\n");
fw.flush();
fw.close();
} catch (IOException e) {
}
 
try {
FileReader fr = new FileReader(f);
//Assuming the file will not have > 50 characters.
char [] destBuf = new char[50];
int size=fr.read(destBuf);
int i = 0;
while(i<size) {
System.out.print(destBuf[i++]);
}
} catch (FileNotFoundException e) {
e.printStackTrace();
}catch (IOException e) {
e.printStackTrace();
}
}
}

This will now display the excat contents of the file.
This is not mentioned in the K&B errata in the site.
Hope am correct.
Thanks
Deepak

[Kelvin Chenhao Lim]

Excellent catch. If I'm not mistaken, most systems will render the remaining zero-value bytes in the array as spaces, so there probably will not be a visible difference to the casual observer. But your correction is absolutely right.