package javabook;
import java.io.*;
import java.util.*;

//首先设计一个学生数据的类
class Student{
    private String name;
    private int score;
    
    public Student(){
        setName("noname");
    }
    
    public Student(String name,int score){
        setName(name);
        this.score=score;
    }
    
    public void setName(String name){
        StringBuilder builder = null;
        if(name!=null)
            builder = new StringBuilder(name);
        else 
            builder = new StringBuilder(15);//StringBuilder(int capacity) 
                             //构造一个不带任何字符的字符串生成器，其初始容量由 capacity 参数指定。
        
        builder.setLength(15);//最长15个字符 1个字符占用2个字节  设置置字符序列的长度 
        this.name = builder.toString();
    }
    
    public void setScore(int score){
        this.score = score;
    }
    
    public String getName(){
        return name;
    }
    
    public int getScore(){
        return score;
    }
    
    
    
     
    public static int size(){
        return 34;
    }
}


public class RandomAccess {
    private static String readName(RandomAccessFile randomAccessfile)throws IOException{
        char[] name = new char[15];
        for(int i = 0;i < name.length;i++)
            name[i]=randomAccessfile.readChar();
        
        /*将空字符取代为空格符并返回
         *replace(char oldChar, char newChar) 返回一个新的字符串，
         *它是通过用 newChar 替换此字符串中出现的所有 oldChar 得到的。
         *String(byte[] bytes)  String的构造方面
         */
        return new String(name).replace('\0', ' ');  

    }
    
    public static void main(String[] args){
        Student[] students={
            new Student("Justi",90),
            new Student("momor",95),
            new Student("Bush",88),
            new Student("catepillar",84)
        };
        try{
            File file = new File("student.data");   //如何没写"/"，就是存在默认包里
            
            /*System.out.println(file.getAbsolutePath());
             *建立RandomAccessFile实例并以读写模式打开文件 "rw"表示读写模式  其中"r"表示读出 "w"表写入 可以用这3个其中1个
             *RandomAccessFile(File file, String mode)   RandomAccessFile(String name, String mode) 
             */ 
            RandomAccessFile randomAccessFile = 
                    new RandomAccessFile(file,"rw");
            
            for(int i = 0;i<students.length;i++){
                //使用对应的write方法写入数据
                randomAccessFile.writeChars(students[i].getName());
                randomAccessFile.writeInt(students[i].getScore()); 
               
            }
            
            
            Scanner scanner = new Scanner(System.in);
            
            System.out.print("读取第几个数据？");
            
            int num = scanner.nextInt();
            
            //使用seek()方法操作存取位置
            randomAccessFile.seek((num-1)*Student.size());
            //randomAccessFile.seek(0);
            Student student = new Student();
            
            //使用对应的read方法读出数据
            student.setName(readName(randomAccessFile));
            student.setScore(randomAccessFile.readInt());
            
            System.out.println("姓名："+student.getName());
            System.out.println("分数"+student.getScore());
            
            //设置关闭文件
            randomAccessFile.close();
            
        }catch(ArrayIndexOutOfBoundsException e){
            e.printStackTrace();
        }
        catch(FileNotFoundException e){
            e.printStackTrace();
        }
        catch(IOException e){
            e.printStackTrace();
        }
        
    }
}