RandomAccessFile(File file, String mode);
mode "r" "rw" .
/* # 4: : RandomFiles.java */
package chapt09;
import java.io.*;
public class RandomFiles {
public static void main(String[] args) {
double data[] = { 1, 10, 50, 200, 5000 };
try {
RandomAccessFile rf =
new RandomAccessFile("temp.txt", "rw");
for (double d: data)
rf.writeDouble(d); //
/* */
for (int i = data.length - 1; i >= 0; i--) {
rf.seek(i * 8);
// double 8-
System. out. println(rf.readDouble());
}
rf.close();
} catch (IOException e) {
System.err.println(e);
}
}
}
:
5000.0
200.0
50.0
10.0
1.0
/ Java , . System java.lang in, InputStream, out, err PrintStream, public static , . , .
PrintWriter, Writer.
( ) PrintWriter:
New PrintWriter(new BufferedWriter(
new FileWriter(new File("file.txt"))));
BufferedWriter - FileWriter, BufferedReader FileReader.
.
// # 5: : DemoWriter.java
package chapt09;
import java.io.*;
public class DemoWriter {
public static void main(String[] args) {
File f = new File("res.txt");
FileWriter fw = null;
try {
fw = new FileWriter(f, true);
} catch (IOException e) {
System. err. println(" " + e);
System. exit (1);
}
BufferedWriter bw = new BufferedWriter(fw);
PrintWriter pw = new PrintWriter(bw);
double [] v = { 1.10, 1.2, 1.401, 5.01 };
for (double version: v)
pw.printf("Java %.2g%n", version);
pw.close();
}
}
res.txt :
Java 1.1
Java 1.2
Java 1.4
Java 5.0
PrintWriter printf(). BufferedWriter FileWriter println(), print(), printf(), format(), write(), append().
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Java 1.1 Java 1.2 , . BufferedReader Reader read() readLine() . FileReader :
new BufferedReader(new FileReader(new File("f.txt")));
:
// # 6: : DemoReader.java
package chapt09;
import java.io.*;
public class DemoReader {
public static void main(String[] args) {
try {
BufferedReader br =
new BufferedReader(new FileReader("res.txt"));
String tmp = "";
while ((tmp = br.readLine())!= null) {
//
String[] s = tmp.split("\\s");
//
for (String res: s)
System. out. println(res);
}
br.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
:
Java
1.1
Java
1.2
Java
1.4
Java
5.0
, .
. . .
, Serializable. . . , , static transient. transient static , , , , . , transient , ( null), static , , .
Serializable , , . . ObjectOutputStream. writeObject(Object ob) ob . ObjectInputStream readObject(), Object. .
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, Serializable : , . .
/* # 7: : Student.java: DemoSerialization.java */
package chapt09;
import java.io.*;
class Student implements Serializable{
protected static String faculty;
private String name;
private int id;
private transient String password;
private static final long serialVersionUID = 1L;
/* */
public Student(String nameOfFaculty, String name,
int id, String password){
faculty = nameOfFaculty;
this. name = name;
this. id = id;
this. password = password;
}
public String toString(){
return "\nfaculty " + faculty + "\nname " + name
+ "\nID " + id + "\npassword " + password;
}
}
public class DemoSerialization {
public static void main(String[] args) {
//
Student goncharenko =
new Student("MMF", "Goncharenko", 1, "G017s9");
System. out. println(goncharenko);
File fw = new File("demo.dat");
try {
ObjectOutputStream ostream =
new ObjectOutputStream(
new FileOutputStream(fw));
ostream.writeObject(goncharenko);
ostream.close();
} catch (IOException e) {
System. err. println(e);
}
Student.faculty="GEO"; // static-
//
File fr = new File("demo.dat");
try {
ObjectInputStream istream =
new ObjectInputStream(
new FileInputStream(fr));
Student unknown =
(Student)istream.readObject();
istream.close();
System. out. println(unknown);
} catch (ClassNotFoundException ce) {
System. err. println(ce);
System. err. println(" ");
} catch (FileNotFoundException fe) {
System. err. println(fe);
System. err. println(" ");
} catch (IOException ioe) {
System. err. println(ioe);
System. err. println(" ");
}
}
}
:
Faculty MMF
Name Goncharenko
ID 1
Password G017s9
Faculty GEO
Name Goncharenko
ID 1
Password null
name id unknown , . e passwrd transient , ( null). faculty, , , , goncharenko MMF, GEO. , .
, , Serializable.
, Serializable, . . , , Serializable, private static final long serialVersionUID. . , , , .
. , static - .
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|
|
. , java.io.InvalidClassException. , .
, . , .
private static final long serialVersionUID.
Serializable Externalizable, :
