JavaIO之RandomAccessFile随机访问文件

package test.java.io;

import java.io.RandomAccessFile;

public class RandomAccFile {
    
    public static void main(String[] args) throws Exception {
        Employee emp1=new Employee("zhangsan",280);
        Employee emp2=new Employee("李四",18);
        Employee emp3=new Employee("tom",22);
        
        //表示该文件可读可写
        RandomAccessFile rdf=new RandomAccessFile("employment.txt","rw"); 
        //rdf.write(emp1.name.getBytes()); //write方法只能作用于英文，对中文
        rdf.writeChars(emp1.name); //在java中不管是英文字符还是中文字符都占有2个字节，它向文件中写入的是字符  16字节
        rdf.writeInt(emp1.age); //写进去的是4个字节，write写的是一个字节 4个字节
        
        rdf.writeChars(emp2.name);
        rdf.writeInt(emp2.age);
        
        //writeChars写入的每个字符占有2个字节
        rdf.writeChars(emp3.name);
        rdf.writeInt(emp3.age);
        
        rdf.close(); //关闭
        
        String strName="";
        //表示文件只能读
        RandomAccessFile readdf=new RandomAccessFile("employment.txt","r"); 
        
        //读李四的内容，跳过20个字节
        readdf.skipBytes(Employee.LEN*2+4);
        //for循环是根据字符来读取的，因此它不用乘以2
        for(int i=0; i<Employee.LEN;i++ )
        {
            strName+=readdf.readChar();//每次只读一个字符
        }
        //byte[] buf = new byte[Employee.LEN*2+4];
        //int len=0;
        //len= readdf.read(buf,0,Employee.LEN);
        //将字节数组转换成字符串
        //String strName=new String(buf,0,Employee.LEN);
        //readdf.read()读取得是一个字节，一旦年龄大于256，就会显示当前值减去256的结果
        //System.out.println(strName+":"+readdf.read());
        System.out.println(strName+": "+readdf.readInt());//readInt获取的是2个字节
    
        //读张三的内容
        strName="";
        readdf.seek(0);
        for(int i=0; i<Employee.LEN;i++ )
        {
            strName+=readdf.readChar();//每次只读一个字符
        }
        System.out.println(strName+": "+readdf.readInt());
        
        //读取tom的数据
        strName="";
        readdf.skipBytes(Employee.LEN*2+4);
        for(int i=0; i<Employee.LEN;i++ )
        {
            strName+=readdf.readChar();//每次只读一个字符
        }
        System.out.println(strName+": "+readdf.readInt());
    }    
} 

package test.java.io;

public class Employee {
    public String name=null;
    public int age=0;
    public final static int LEN=8;
    public Employee(String name,int age)
    {
        if(name.length()>LEN)
        {
            name=name.substring(0,LEN);
        }
        else
        {
            while(name.length()<8)
            {
                name+='u0000';//空格李四
            }
        }
        this.name=name;
        this.age=age;
        
    }
        
}