java 读写txt，写入的时候为甚么我只可以写入一个对象？求正解

tianshuai12 2010-06-08 01:03:28

package 实验七第二题;

import java.io.BufferedReader;
import java.io.FileWriter;
import java.io.IOException;
import java.io.InputStreamReader;

public class Student {
public int num,grade;
public String name;
public Student() throws IOException{
FileWriter fw =new FileWriter("D:\\data.txt");
InputStreamReader ir=new InputStreamReader(System.in);
BufferedReader in =new BufferedReader(ir);
System.out.println("请输入编号");
num=Integer.parseInt(in.readLine());
fw.write(" "+num);
BufferedReader en =new BufferedReader(ir);
System.out.println("请输入姓名");
name=en.readLine();
fw.write(" "+name);
BufferedReader gn =new BufferedReader(ir);
System.out.println("请输入成绩");
grade=Integer.parseInt(gn.readLine());
fw.write(" "+grade);
in.close();
en.close();
gn.close();
fw.close();
}
public static void main(String[] args) throws IOException {
Student A=new Student();
Student B=new Student();
Student C=new Student();
Student D=new Student();
Student E=new Student();

}

}
//如果下面只定义一个对象的话可以通过，如果多个对象的话报错

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xu3352 2010-06-08

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用 8楼的构造

xu3352 2010-06-08

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写入文件时候用追加方式

tubage408 2010-06-08

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public FileWriter(File file,
boolean append)
throws IOException

pixiaozheng 2010-06-08

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作业题。。。

lodachi 2010-06-08

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[Quote=引用 2 楼 truediego 的回复:]

你每new一个student，就一个
FileWriter fw =new FileWriter("D:\\data.txt");

已经把原来的覆盖掉了
[/Quote]正解
把对象写入文件可以用对象流，ObjectInputStream/ObjectOutputStream，多个同类对象可以放到List或者Map里再写入文件

dr_lou 2010-06-08

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至于为什么只有一个，就是LS说的了，文件覆盖问题。

dr_lou 2010-06-08

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你的构造函数真是。。。。

package com.xuz.datastruct.csdn;



import java.io.BufferedReader;

import java.io.FileWriter;

import java.io.IOException;

import java.io.InputStreamReader;



public class Student {

	public int num, grade;

	public String name;



	public Student() throws IOException {

		FileWriter fw = new FileWriter("D:\\data.txt");

		InputStreamReader ir = new InputStreamReader(System.in);

		BufferedReader in = new BufferedReader(ir);

		System.out.println("请输入编号");

		num = Integer.parseInt(in.readLine());

		fw.write(" " + num);

		System.out.println("请输入姓名");

		name = in.readLine();

		fw.write(" " + name);

		System.out.println("请输入成绩");

		grade = Integer.parseInt(in.readLine());

		fw.write(" " + grade);

		fw.flush();

		fw.close();

	}



	public static void main(String[] args) throws IOException {

		Student A = new Student();

		Student B = new Student();

		Student C = new Student();

		Student D = new Student();

		Student E = new Student();



	}



}