What is the method of Java RandomAccessFile operation
This article mainly explains "what is the method of Java RandomAccessFile operation". Interested friends may wish to have a look at it. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn "what is the method of Java RandomAccessFile operation"?
A brief introduction
RandomAccessFile:java provides access to the contents of a file, either reading or writing to it.
RandomAccessFile supports random access to files and can access any location of the file
1. Java file model
The files on the hard disk are stored in byte byte byte and are a collection of data.
2. Open the file
There are two modes "rw" (read-write) "r" (read-only)
RandomAccessFile raf = new RandomAccessFile (file, "rw")
File pointer: when opening a file, the pointer is at the beginning of pointer = 0
3. Write documents
Raf.write (int)-> writes only one byte (the last 8 bits), while the pointer points to the next location, ready to write again
4. Reading method
Int b = raf.read ()-> read a byte
5. Be sure to close the file after reading and writing
Two code implementation
Package com.imooc.io;import java.io.File;import java.io.IOException;import java.io.RandomAccessFile;import java.util.Arrays;public class RafDemo {
/ * * @ param args * / public static void main (String [] args) throws IOException {
File demo = new File ("demo")
If (! demo.exists () demo.mkdir ()
File file = new File (demo, "raf.dat")
If (! file.exists () file.createNewFile ()
RandomAccessFile raf = new RandomAccessFile (file, "rw")
/ / position of the pointer
System.out.println (raf.getFilePointer ())
Raf.write ('A')
/ / only one byte was written
System.out.println (raf.getFilePointer ())
Raf.write ('B')
Int I = 0x7fffffff
/ / you can only write one byte at a time with the write method. If you want to write I, you have to write raf.write (I > 24) 4 times; / / High 8-bit raf.write (I > 16); raf.write (I > > 8); raf.write (I)
System.out.println (raf.getFilePointer ())
/ / you can write an int raf.writeInt (I) directly
String s = "medium"
Byte [] gbk = s.getBytes ("gbk")
Raf.write (gbk)
System.out.println (raf.length ())
/ / to read the file, you must move the pointer to the header
Raf.seek (0)
/ / read all the contents of the file into the byte array at one time
Byte [] buf = new byte [(int) raf.length ()]
Raf.read (buf)
System.out.println (Arrays.toString (buf))
For (byte b: buf) {
System.out.println (Integer.toHexString (b & 0xff) + "")
}
Raf.close ()
}}
Third, realize the effect
01612 [65, 66, 127,-1,-1,-1,127,-1,-1,-1,-42,-48] 41427fffffff7fffffffd6d0
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