java中RandomAccessFile类用法
RandomAccessFile类
只能访问文件,不能操作其他io设备
支持随机访问
在读写等长记录文件有优势
实例:
import java.io.*; class Employee { private String name; private int age; public static final int LEN = 8; String getName() { return name; } int getAge() { return age; } Employee(String name, int age) { if (name.length() > LEN) { // 为了构造等长记录 this.name = name.substring(0, LEN-1); } else { this.name = name; while (this.name.length() < LEN) { this.name += '\u0000'; } } this.age = age; } } public class RandomAccessFileTest { public static void main(String [] args) { Employee e1 = new Employee("Ronnie", 37); Employee e2 = new Employee("John", 37); Employee e3 = new Employee("Mark", 37); try { RandomAccessFile randFile = new RandomAccessFile("employee.txt", "rw"); //randFile.write(e1.getName().getBytes()); // 如果name有中文,会出现问题,因为一个英文字符转换为一个字节,一个中文字符转换为两个字节,可以用writeChars函数改写 randFile.writeChars(e1.getName()); //- randFile.writeInt(e1.getAge()); //randFile.write(e2.getName().getBytes()); randFile.writeChars(e1.getName()); //- randFile.writeInt(e2.getAge()); //randFile.write(e3.getName().getBytes()); randFile.writeChars(e1.getName()); //- randFile.writeInt(e3.getAge()); randFile.close(); } catch (Exception e) { e.printStackTrace(); } try { //byte[] nameBuf = new byte[Employee.LEN]; RandomAccessFile randFile = new RandomAccessFile("employee.txt", "r"); //randFile.skipBytes(12); randFile.skipBytes(20); //- //int len = randFile.read(nameBuf); //String name = new String(nameBuf, 0, len); String name = "";//- for (int i = 0; i < Employee.LEN; ++i) { //- name += randFile.readChar(); //- }//- System.out.println(name.trim() + ":" + randFile.readInt()); name = ""; //- randFile.seek(0); // 绝对定位 //len = randFile.read(nameBuf); //name = new String(nameBuf, 0, len); for (int i = 0; i < Employee.LEN; ++i) { //- name += randFile.readChar(); //- } //- System.out.println(name.trim() + ":" + randFile.readInt()); name = ""; //- //randFile.skipBytes(12); randFile.skipBytes(20); //- //len = randFile.read(nameBuf); //name = new String(nameBuf, 0, len); for (int i = 0; i < Employee.LEN; ++i) { //- name += randFile.readChar(); //- } //- System.out.println(name.trim() + ":" + randFile.readInt()); randFile.close(); } catch (Exception e) { e.printStackTrace(); } } }
注释部分为按字节写入时的程序,带//-为原来的代码
其他函数请参照jdk文档