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分享请教：如何将HashMap中的内容写入到文件？
题目：完成一个学生管理程序，使用学号作为键添加5个学生对象，并可以将全部的信息保存在文件中，
可以实现对学生信息的全面查找，输出全部学生信息的功能。
*/
import java.util.*;
import java.io.*;
class Student implements Serializable{
int num;
String name;
double scores[]; //三门课程成绩
double aver; //平均成绩
public Student(){
this.scores=new double[3];
}
public Student(int num,String name,double score1,double score2,double score3){
this ();
this.setNumber(num);
this.setName(name);
this.setScores(score1,score2,score3);
this.aver=(this.scores[0]+this.scores[1]+this.scores[2])/3;
}
public void setNumber(int num){
this.num=num;
}
public void setName(String name){
this.name=name;
}
public void setScores(double score1,double score2,double score3){
this.scores[0]=score1;
this.scores[1]=score2;
this.scores[2]=score3;
}
public int getNumber(){
return num;
}
public String getName(){
return name;
}
public double[] getScores(){
return scores;
}
public double getAver(){
return aver;
}
public String toString(){
return "学号："+this.num+"姓名："+this.name+"\n"+"成绩————>"+"语文："+this.scores[0]+"数学："+this.scores[1]+"英语："+this.scores[2]+"平均成绩："+this.aver;
}
}
/*
Scanner sc=new Scanner(System.in);
sc.next()即为输入的内容;
*/
public class Test_12{
public static void main(String...args){
HashMap<Integer,Student> stu=new HashMap<Integer,Student>();
File file=new File("D:\\sb\\Stu_info.data");
Student zhangsan=new Student(18,"张三",78,85,92);
Student lisi=new Student(15,"李四",85,87,74);
Student wangwu=new Student(20,"王五",75,98,96);
Student zhaoliu=new Student(9,"赵六",93,98,93);
stu.put(18,zhangsan);
stu.put(15,lisi);
stu.put(20,wangwu);
stu.put(9,zhaoliu);
}
//写到这一步不知道该怎么写了？
}
//怎么将HashMap中的内容保存到文件，又怎么读取文件？希望各位朋友给点意见或思路.
...全文
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liangs0620 2013-02-02
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把得到的hashmap作为属性封装到一个对象中再进行实例化保存，在强制类型转换的时候就不会报unchecked警告了，代码如下
package test;
//题目：完成一个学生管理程序，使用学号作为键添加5个学生对象，并可以将全部的信息保存在文件中，
//可以实现对学生信息的全面查找，输出全部学生信息的功能。
//
import java.util.*;
import java.io.*;
class Student implements Serializable {
/**
*
*/
private static final long serialVersionUID = 1L;
int num;
String name;
double scores[]; // 三门课程成绩
double aver; // 平均成绩
public Student() {
this.scores = new double[3];
}
public Student(int num, String name, double score1, double score2,
double score3) {
this();
this.setNumber(num);
this.setName(name);
this.setScores(score1, score2, score3);
this.aver = (this.scores[0] + this.scores[1] + this.scores[2]) / 3;
}
public void setNumber(int num) {
this.num = num;
}
public void setName(String name) {
this.name = name;
}
public void setScores(double score1, double score2, double score3) {
this.scores[0] = score1;
this.scores[1] = score2;
this.scores[2] = score3;
}
public int getNumber() {
return num;
}
public String getName() {
return name;
}
public double[] getScores() {
return scores;
}
public double getAver() {
return aver;
}
public String toString() {
return "学号：" + this.num + "姓名：" + this.name + "\n" + "成绩————>" + "语文："
+ this.scores[0] + "数学：" + this.scores[1] + "英语："
+ this.scores[2] + "平均成绩：" + this.aver;
}
}
/*
* Scanner sc=new Scanner(System.in); sc.next()即为输入的内容;
*/
public class Test_12 {
public static void main(String[] args) throws Exception {
HashMap<Integer, Student> stu = new HashMap<Integer, Student>();
File file = new File("Stu_info.obj");
Student zhangsan = new Student(18, "张三", 78, 85, 92);
Student lisi = new Student(15, "李四", 85, 87, 74);
Student wangwu = new Student(20, "王五", 75, 98, 96);
Student zhaoliu = new Student(9, "赵六", 93, 98, 93);
stu.put(18, zhangsan);
stu.put(15, lisi);
stu.put(20, wangwu);
stu.put(9, zhaoliu);
// 写
FileOutputStream fos = null;
ObjectOutputStream oos = null;
fos = new FileOutputStream(file);
oos = new ObjectOutputStream(fos);
oos.writeObject(new Inner(stu));
oos.flush();
oos.close();
// 读
FileInputStream fis = null;
ObjectInputStream ois = null;
fis = new FileInputStream(file);
ois = new ObjectInputStream(fis);
Inner inner = null;
HashMap<Integer, Student> stuRead = null;
try {
inner = (Inner) ois.readObject();// ！！！！！！
} catch (EOFException e) {
e.printStackTrace();
}finally{
ois.close();
}
stuRead = inner.stu;
// 测试
for (Map.Entry<Integer, Student> item : stuRead.entrySet()) {
System.out.println(item.getValue());
}
}
}
class Inner implements Serializable {
/**
* 这个类的初衷是想将前面获得的HashMap作为对象属性进行序列化，因为如果直接将Hashmap序列化的话
* 在读取文件的时候（readobject），进行强制类型转换时，涉及到泛型，会报unchecked警告··· 仅此而已··
*/
private static final long serialVersionUID = 2L;
HashMap<Integer, Student> stu;
public Inner(HashMap<Integer, Student> stu) {
this.stu = stu;
}
}
liangs0620 2013-02-01
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因为涉及到泛型，什么instanceOf等等方法都用不了，暂时想不到什么办法···我觉得这个警告可以无视，反正知道取出来的肯定是HashMap，也不需要为了好看添加@SuppressWarnings
a673921712 2013-02-01
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除了@SuppressWarnings，还有没有别的方法？
liangs0620 2013-02-01
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在强制类型转换的时候···
stuRead = (HashMap<Integer, Student>) ois.readObject();
a673921712 2013-02-01
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@SuppressWarnings("unchecked")
程序里的集合容器都加泛型了，怎么还有这个"unchecked"提示，还有哪里没加吗？
a673921712 2013-02-01
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感谢几位的回答。
致追风 2013-02-01
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用BufferedWriter试试。我改了一下你的代码，可以输出文件。
import java.io.File;
import java.io.IOException;
import java.util.HashMap;
public class Test_12 {
public static void main(String[] args) throws IOException {
java.io.BufferedWriter bufferWriter = null;
File file =null;
try {
file=new File("D:\\sb\\Stu_info.data");
HashMap<Integer, Student> stu = new HashMap<Integer, Student>();
Student zhangsan = new Student(18, "张三", 78, 85, 92);
Student lisi = new Student(15, "李四", 85, 87, 74);
Student wangwu = new Student(20, "王五", 75, 98, 96);
Student zhaoliu = new Student(9, "赵六", 93, 98, 93);
stu.put(18, zhangsan);
stu.put(15, lisi);
stu.put(20, wangwu);
stu.put(9, zhaoliu);
bufferWriter = new java.io.BufferedWriter(new java.io.FileWriter(file));
bufferWriter.write(stu.get(18).toString());
bufferWriter.write(stu.get(15).toString());
bufferWriter.write(stu.get(20).toString());
bufferWriter.write(stu.get(9).toString());
bufferWriter.flush();
} finally {
if (bufferWriter != null) {
try {
bufferWriter.close();
} catch (Exception e) {
}
}
}
}
}
菖蒲老先生 2013-02-01
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public class Test_12{
public static void main(String... args) throws Exception {
HashMap<Integer, Student> stu = new HashMap<Integer, Student>();
File file = new File("D:\\sb\\Stu_info.data");
Student zhangsan = new Student(18, "张三", 78, 85, 92);
Student lisi = new Student(15, "李四", 85, 87, 74);
Student wangwu = new Student(20, "王五", 75, 98, 96);
Student zhaoliu = new Student(9, "赵六", 93, 98, 93);
stu.put(18, zhangsan);
stu.put(15, lisi);
stu.put(20, wangwu);
stu.put(9, zhaoliu);
write(stu);
read();
}
// 写到这一步不知道该怎么写了？
private static void write(Map<Integer, Student> map) throws Exception {
PrintWriter pw = new PrintWriter("D:\\Stu_info.data", "utf-8");
StringBuilder sb = new StringBuilder();
for (Student s : map.values()) {
sb.append(s.getNumber() + "\t");
sb.append(s.getName() + "\t");
sb.append(s.getScores()[0] + "\t");
sb.append(s.getScores()[1] + "\t");
sb.append(s.getScores()[2] + "\n");
}
pw.write(sb.toString());
pw.close();
}
private static void read() throws Exception {
BufferedReader reader = new BufferedReader(new InputStreamReader(new FileInputStream("D:\\Stu_info.data"), "utf-8"));
String line = null;
while ((line = reader.readLine()) != null) {
System.out.println(line);
}
}
}
liangs0620 2013-02-01
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自己看吧 不懂再说
package test;
//题目：完成一个学生管理程序，使用学号作为键添加5个学生对象，并可以将全部的信息保存在文件中，
//可以实现对学生信息的全面查找，输出全部学生信息的功能。
//
import java.util.*;
import java.io.*;
class Student implements Serializable {
int num;
String name;
double scores[]; // 三门课程成绩
double aver; // 平均成绩
public Student() {
this.scores = new double[3];
}
public Student(int num, String name, double score1, double score2,
double score3) {
this();
this.setNumber(num);
this.setName(name);
this.setScores(score1, score2, score3);
this.aver = (this.scores[0] + this.scores[1] + this.scores[2]) / 3;
}
public void setNumber(int num) {
this.num = num;
}
public void setName(String name) {
this.name = name;
}
public void setScores(double score1, double score2, double score3) {
this.scores[0] = score1;
this.scores[1] = score2;
this.scores[2] = score3;
}
public int getNumber() {
return num;
}
public String getName() {
return name;
}
public double[] getScores() {
return scores;
}
public double getAver() {
return aver;
}
public String toString() {
return "学号：" + this.num + "姓名：" + this.name + "\n" + "成绩————>" + "语文："
+ this.scores[0] + "数学：" + this.scores[1] + "英语："
+ this.scores[2] + "平均成绩：" + this.aver;
}
}
/*
* Scanner sc=new Scanner(System.in); sc.next()即为输入的内容;
*/
public class Test_12 {
@SuppressWarnings("unchecked")
public static void main(String... args) throws Exception {
HashMap<Integer, Student> stu = new HashMap<Integer, Student>();
File file = new File("Stu_info.obj");
Student zhangsan = new Student(18, "张三", 78, 85, 92);
Student lisi = new Student(15, "李四", 85, 87, 74);
Student wangwu = new Student(20, "王五", 75, 98, 96);
Student zhaoliu = new Student(9, "赵六", 93, 98, 93);
stu.put(18, zhangsan);
stu.put(15, lisi);
stu.put(20, wangwu);
stu.put(9, zhaoliu);
// 写
FileOutputStream fos = null;
ObjectOutputStream oos = null;
fos = new FileOutputStream(file);
oos = new ObjectOutputStream(fos);
oos.writeObject(stu);
oos.flush();
oos.close();
// 读
FileInputStream fis = null;
ObjectInputStream ois = null;
fis = new FileInputStream(file);
ois = new ObjectInputStream(fis);
HashMap<Integer, Student> stuRead = new HashMap<Integer, Student>();
stuRead = (HashMap<Integer, Student>) ois.readObject();
ois.close();
// 测试
for (Map.Entry<Integer, Student> item : stuRead.entrySet()) {
System.out.println(item.getValue());
}
}
}
// 怎么将HashMap中的内容保存到文件，又怎么读取文件？希望各位朋友给点意见或思路.
nmyangym 2013-02-01
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1 可以写成Object流
2 写成文本文件。（这个简单，就把对象写入文件，因为里面有toString了）。
a673921712 2013-02-01
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来人撒，别沉下去了。
a673921712 2013-02-01
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怎么写？给点参考，Map中的元素是一对键值，不是字符串。
forgetsam 2013-02-01
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看你要什么格式的，流读写就可以。
