FileWriter
In this chapter you will learn:
Use FileWriter
FileWriter creates a Writer that you can use characters to write to a file. Its most commonly used constructors are shown here:
FileWriter(String filePath)
filePathis the full path name of a fileFileWriter(String filePath, boolean append)
If append is true, then output is appended to the end of the file.FileWriter(File fileObj)
fileObjis a File object that describes the file.FileWriter(File fileObj, boolean append)
If append is true, then output is appended to the end of the file.
FileWriter will create a file before opening it if the file does not exist.
Attempt to open a read-only file results an IOException.
import java.io.FileWriter;
/* j a v a 2 s. c o m*/
public class Main {
public static void main(String args[]) throws Exception {
FileWriter fw = new FileWriter(args[0]);
for (int i = 0; i < 12; i++) {
fw.write("Line " + i + " java2s.com \n");
}
fw.close();
}
}
The following create a FileWriter to write to LPT1.
import java.io.FileWriter;
import java.io.IOException;
import java.io.PrintWriter;
//from j a v a 2 s . c o m
public class MainClass {
public static void main(String[] args) {
try {
FileWriter fw = new FileWriter("LPT1:");
PrintWriter pw = new PrintWriter(fw);
String s = "www.java2s.com";
int i, len = s.length();
for (i = 0; len > 80; i += 80) {
pw.print(s.substring(i, i + 80));
pw.print("\r\n");
len -= 80;
}
if (len > 0) {
pw.print(s.substring(i));
pw.print("\r\n");
}
pw.close();
} catch (IOException e) {
System.out.println(e);
}
}
}
Copy a file with FileReader and FileWriter
FileReader and FileWriter can work together to copy a text file
character by character.
import java.io.File;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
/* j a v a 2 s. com*/
public class Main {
public static void main(String[] args) throws IOException {
File inputFile = new File("farrago.txt");
File outputFile = new File("outagain.txt");
FileReader in = new FileReader(inputFile);
FileWriter out = new FileWriter(outputFile);
int c;
while ((c = in.read()) != -1)
out.write(c);
in.close();
out.close();
}
}
Append to a text file FileWriter
When constructing a FileWriter with given a File object,
if the second argument is true, then bytes will be written to the end of the file
not the beginning.
import java.io.BufferedWriter;
import java.io.FileWriter;
//from j a va2 s .c o m
public class Main {
public static void main(String[] argv) throws Exception {
BufferedWriter out = new BufferedWriter(new FileWriter("filename", true));
out.write("aString");
out.close();
}
}
Next chapter...
What you will learn in the next chapter:
- How to use Java BufferedWriter to write character faster
- Wrap System.out with BufferedWriter
- Write portion of a string with BufferedWriter
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