黑马程序员_java输出输入流练习题

来源：互联网发布：orbitcontrols.js 编辑：程序博客网时间：2024/05/16 08:17

---------------------- android培训、java培训、期待与您交流！ ----------------------

题目：编写一个程序, 可以从键盘输入读取多个学生成绩, 输入quit时退出.程序将输入数据写入stu.txt文件(UTF-8), 文件中按照学生成绩总分排序.

思路： 1、读取键盘输入?

读键盘用System.in，但是读的是字节，所以需要转成InputStreamReader来读字符，由于成绩是一行一行输入，所以需要转成BufferedReader来读取一行

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

2、题目要求读取多个学生成绩，并且输入quit时退出

所以需要用到循环，不确定循环次数，所以用while，什么时候循环结束？当输入quit时结束。用"quit".equals("读取的内容")即可

BufferedReader br = new BufferedReader(new InputStreamReader(System.in));while(true){String line = br.readLine();if("quit".equals(line))break;}

3、要把读到到输入记录下来

每一行输入的内容大概是：姓名,77,88,55 。题目要求读取后还按照原格式存储，并且按成绩总分排序。可以把这些数据封装成一个对象，写一个Student类。

属性：private String name; private int chinese; private int math; private int english; private int sum;

构造函数：

public Student(String name, int chinese, int math, int english) {this.name = name;this.chinese = chinese;this.math = math;this.english = english;this.sum = chinese + math + english;}

4、存入到什么容器

每一行数据是一个对象，并且存入多个对象，并且按照总分排序，所以用TreeSet

存入TreeSet会自动排序，但是存入的是对象，所以需要在Student类上实现Comparable接口，实现compareTo方法

public int compareTo(Student o) {int sumGap = this.sum - o.sum;return sumGap != 0 ? sumGap : this.name.compareTo(o.name);}

5、再把TressSet的数据写出到文件里

Student类代码：

public class Student implements Comparable<Student> {private String name;private int chinese;private int math;private int english;private int sum;public Student(String name, int chinese, int math, int english ) {super();this.name = name;this.chinese = chinese;this.math = math;this.english = english;this.sum = chinese + math + english;}public int compareTo(Student o) {return o.sum - this.sum;}public String toString() {return name + "," + chinese + "," + math + "," + english + "," + sum;}}

主程序类代码：

import java.io.BufferedReader;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStreamReader;import java.io.OutputStreamWriter;import java.util.TreeSet;public class Exercise3 {public static void main(String[] args) throws IOException {TreeSet<Student> set = new TreeSet<Student>();BufferedReader br = new BufferedReader(new InputStreamReader(System.in));while(true){String line = br.readLine();if("quit".equals(line))break;String[] arr = line.split(",");Student stu = new Student(arr[0],Integer.parseInt(arr[1]),Integer.parseInt(arr[2]),Integer.parseInt(arr[3]));set.add(stu);}OutputStreamWriter osw =new  OutputStreamWriter(new FileOutputStream("stu.txt",true));for (Student student : set) {osw.write(student.toString());}osw.close();}private static void demo() throws IOException, FileNotFoundException {TreeSet<Student> set = new TreeSet<Student>();BufferedReader br = new BufferedReader(new InputStreamReader(System.in));while(true){String line = br.readLine();if("quit".equals(line))break;String[] arr = line.split(",");Student stu = new Student(arr[0], Integer.parseInt(arr[1]), Integer.parseInt(arr[2]), Integer.parseInt(arr[3]));set.add(stu);}OutputStreamWriter osw = new OutputStreamWriter(new FileOutputStream("stu.txt",true));for (Student student : set) {osw.write(student.toString()+"\r\n");}osw.close();}}

---------------------- android培训、java培训、期待与您交流！ ----------------------详细请查看：http://edu.csdn.net/heima