[Java开发之路]（7）RandomAccessFile类详解

package com.qunar.bean;
 
import java.io.File;
import java.io.RandomAccessFile;
 
public class FileDemo {
	
	public static void main(String[] args) {
		String pathname = "D:\\Recommended system.txt";
		// 创建文件实例
		File file = new File(pathname);
		
		try {
			// 判断文件是否存在
			if(!file.exists()){
				file.createNewFile();
			}//if
			
			// 读写方式打开文件
			RandomAccessFile randomAccessFile = new RandomAccessFile(file, "rw");
			
			// 写值
			for(int i = 0;i < 5;++i){
				randomAccessFile.writeInt(i);
			}//for
			
			// 将文件指针移到第二个Int值后
			randomAccessFile.seek(2*4);
			// 覆盖第三个Int值
			randomAccessFile.writeInt(6);
			
			// 文件指针指向文件开头
			randomAccessFile.seek(0);
			// 输出
			for (int i = 0;i < 5;++i) {
				System.out.print(randomAccessFile.readInt()+" ");
			}//for
			
			randomAccessFile.close();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

package com.qunar.bean;
 
import java.io.File;
import java.io.RandomAccessFile;
import java.util.Arrays;
 
public class FileDemo {
	
	public static void main(String[] args) {
		String pathname = "D:\\Recommended system.txt";
		// 创建文件实例
		File file = new File(pathname);
		
		try {
			// 判断文件是否存在
			if(!file.exists()){
				file.createNewFile();
			}//if
			
			// 读写方式打开文件
			RandomAccessFile randomAccessFile = new RandomAccessFile(file, "rw");
			System.out.println("当前所处的位置："+randomAccessFile.getFilePointer());
			
			// write 从当前指针开始写入，写入一个字节
			randomAccessFile.write(‘A‘);
			System.out.println("当前所处的位置："+randomAccessFile.getFilePointer());
			
			randomAccessFile.write(‘B‘);
			
			int num = 0x7fffffff;
			// 如果用write方法，每次只能写一个字节，需要写4次
			randomAccessFile.write(num >>> 24);
			randomAccessFile.write(num >>> 16);
			randomAccessFile.write(num >>> 8);
			randomAccessFile.write(num);
			System.out.println("当前所处的位置："+randomAccessFile.getFilePointer());
			
			// 或者是用writeInt方法 一次写入
			randomAccessFile.writeInt(num);
			System.out.println("当前所处的位置："+randomAccessFile.getFilePointer());
			
			// 文件指针指向文件开头
			randomAccessFile.seek(0);
			// 一次性读取 把文件中内容都读到字节数组中
			byte[] buffer = new byte[(int)randomAccessFile.length()];
			randomAccessFile.read(buffer);
			
			for (byte b : buffer) {
				// 16进制输出
				System.out.print(Integer.toHexString(b)+" ");
			}//for
			
			randomAccessFile.close();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

package com.qunar.bean;
 
import java.io.File;
import java.io.RandomAccessFile;
 
public class FileDemo {
	
	public static void main(String[] args) {
		String pathname = "D:\\Recommended system.txt";
		// 创建文件实例
		File file = new File(pathname);
		
		try {
			RandomAccessFile randomAccessFile = new RandomAccessFile(file, "rw");  
			
			// 以下向file文件中写数据  
			// 占4个字节  
			randomAccessFile.writeInt(2015);
			// 占8个字节
			randomAccessFile.writeDouble(12.23);  
			// 占2个字节
			randomAccessFile.writeShort(19);  
			System.out.println("当前位置："+randomAccessFile.getFilePointer());
			randomAccessFile.writeUTF("欢迎来到小斯的博客");
			System.out.println("当前位置："+randomAccessFile.getFilePointer());
			// 占2个字节
			randomAccessFile.writeChar(‘Y‘);  
			System.out.println("当前位置："+randomAccessFile.getFilePointer());
			randomAccessFile.writeUTF("小斯的博客欢迎你");
			
			// 把文件指针位置设置到文件起始处  
			randomAccessFile.seek(0);
			System.out.println("读取一个Int值："+randomAccessFile.readInt());  
			System.out.println("读取一个Double值："+randomAccessFile.readDouble());  
			System.out.println("读取一个Short值："+randomAccessFile.readShort()); 
			System.out.println("读取一个字符串："+randomAccessFile.readUTF());  
			// 将文件指针跳过2个字节
			randomAccessFile.skipBytes(2);  
			System.out.println("读取一个字符串："+randomAccessFile.readUTF());  
			
			randomAccessFile.close();
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}