Useful File java.io Mini API
Java io is a very extensive library. There are numerous ways and combinations to write/read data on a file. This article summaries some very useful classes in java.io
package.
Here is a table from OCP Java SE 8 Programmer II Exam Guide (Exam 1Z0-809) that summarizes the basic classes in file io.
java.io Class | Extends From | Key Constructor(s) | Key Methods |
---|---|---|---|
File |
Object |
File, String String String, String |
createNewFile() delete() exists() isDirectory() isFile() list() mkdir() renameTo() |
FileWriter |
Writer |
File String |
close() flush() write() |
BufferedWriter |
Writer |
Writer |
close() flush() newLine() write() |
PrintWriter |
Writer |
File String OuputStream Writer |
close() flush() format() printf() print() println() write() |
FileOutputStream |
OutputStream |
File String |
close() write() |
FileReader |
Reader |
File String |
read() |
BufferedReader |
Reader |
Reader |
read() readLine() |
FileInputStream |
InputStream |
File String |
read() close() |
Examples
import java.io.*;
class Writer1 {
public static void main(String... args) {
try {
boolean newFile = false;
File file = new File("fileWrite1.txt");
System.out.println(file.exists());
newFile = file.createNewFile();
System.out.println(newFile);
System.out.println(file.exists());
} catch(IOException e) {}
}
}
class Writer2 {
public static void main(String... args) {
char[] in = new char[50];
int size = 0;
try {
File file = new File("fileWrite2.txt");
FileWriter fw = new FileWriter(file);
fw.write("howdy\nfolks\n");
fw.flush();
fw.close();
FileReader fr = new FileReader(file);
size = fr.read(in);
System.out.print(size + " ");
for(char c: in) {
System.out.print(c);
}
fr.close();
} catch(IOException e) { }
}
}
class Writer3 {
public static void main(String... args) {
byte[] in = new byte[50];
int size = 0;
File file = new File("fileWrite3.txt");
try(FileOutputStream outStream = new FileOutputStream(file);
FileInputStream inStream = new FileInputStream(file)) {
String s = "howdy\nfolks\n";
outStream.write(s.getBytes());
outStream.flush();
size = inStream.read(in);
System.out.print(size + " ");
for(byte b: in) {
System.out.print((char) b);
}
} catch(IOException e) {}
}
}
class Writer4 {
public static void main(String... args) {
File file = new File("fileWrite4.txt");
try(PrintWriter pw = new PrintWriter(file);
BufferedReader br = new BufferedReader(new FileReader(file))) {
pw.println("howdy");
pw.println("folks");
pw.flush();
String line = null;
while(true) {
line = br.readLine();
if (line == null) break;
System.out.println(line);
}
} catch(IOException e) {}
}
}
Comments
Post a Comment