randomfiles.java

国外的数据结构与算法分析用书

import java.io.*;

/**	A small program that reads in a file containing a copy of its source code and
	displays the first 30 characters.  It then writes additional text past the
	end of the file. */
public class RandomFiles
{
	public static void main(String[] args) throws IOException
	{
		RandomAccessFile raf = new RandomAccessFile("RandomFiles.copy", "rw");
		long size = raf.length(); // get file length
		System.out.println("The file is: " + size + " bytes long.");
		System.out.println("The first 30 bytes");
		String fromFile = new String();
		for (int i = 0; i < 30; i++)
		{
			int c = raf.read(); // get single character from file
			fromFile += (char) c; // add character to end of string
		}
		System.out.println(fromFile); // display the first 30 characters

		raf.seek(size - 5); // move index pointer 5 spaces from the end of file
		raf.writeBytes("This string will replace the last five characters ");
		raf.writeBytes("and increase the file size."); 
		raf.close();
	}
}