Java: IO 学习小结
源:
键盘 System.in 硬盘 FileStream 内存 ArrayStream
目的:
控制台 System.out 硬盘 FileStream 内存 ArrayStream
处理大文件或者多线程下载\上传
RandomAccessFile 或者内存映射文件
方便对对象的永久化存储和调用
ObjectStream
方便操作打印流
PrintWriter 和 PrintStream
序列流,对多个流进行合并
SequenceInpuntStream
管道流,输入和输出可以直接连接,通过结合线程使用
PipedInputStream PipedOutputStream
方便操作基本数据类型
DataInputStream DataOutputStream
方便操作字节数组
ByteArrayInputStream ByteArrayOutputStream
方便操作字符数组
CharArrayReader CharArrayWriter
方便操作字符串
StringReader StringWriter
字符编码:
字符流的出现为了方便操作字符,更重要的是加入了字符转换.
字符转换通过转换流来完成
InputStreamReader
OutputStreamWriter
在两个对象进行构造时可加入字符集
编码;
字符串变成字节数组
String --> byte[] str.getBytes()(按照平台默认的字符集) str.getBytes(String charsetName)(按照指定字符集编码)
解码:
字节数组变字符串
byte[] --> String new String(byte[]) new String(byte[], charsetName)(按照指定的字符编码)
常见的字符集:
ASCII:美国标准信息交换码
用一个字节的7位就可以表示
IOS8859-1:拉丁码表\欧洲码表
用一个字节的8位表示
GB2312:中国的中文编码表
GBK:中文编码表升级,融合了更多的中文字符
Unicode:国际标准编码,融合了多种文字
所有字符都用两个字节表示,java语言就是用的unicode
UTF-8:用3个字节来表示一个汉字
练习题:
在屏幕上输入学生姓名,数学成绩,语文成绩,英语成绩,形如"owen,99,99,99",将学生成绩按照总分排列,并且储存在本地文件中.
1 package Day20; 2 import java.io.*; 3 import java.util.Collections; 4 import java.util.Comparator; 5 import java.util.Set; 6 import java.util.TreeSet; 7 8 public class StudentInfo { 9 10 public static void main(String[] args) { 11 OutputStream out = null; 12 try{ 13 out = new FileOutputStream("exam.txt"); 14 //Set<Student> stus = StudentTool.getStudents(); 15 Comparator<Student> cmp = Collections.reverseOrder(); 16 Set<Student> stus = StudentTool.getStudents(cmp); 17 StudentTool.write2File(stus, out); 18 } 19 catch(IOException e){ 20 throw new RuntimeException("写入异常"); 21 } 22 finally{ 23 try{ 24 if(out!=null) 25 out.close(); 26 } 27 catch(IOException e){ 28 throw new RuntimeException("关闭写入动作遇到错误"); 29 } 30 } 31 } 32 33 } 34 35 class Student implements Comparable 36 { 37 private String name; 38 private double math,cn,en,sum; 39 40 Student(String name, double math, double cn, double en){ 41 this.name = name; 42 this.math = math; 43 this.cn = cn; 44 this.en = en; 45 sum = math + cn + en; 46 47 } 48 public String getName(){ 49 return name; 50 } 51 public double getSum(){ 52 return sum; 53 } 54 @Override 55 public int compareTo(Object o){ 56 if(!(o instanceof Student)) 57 throw new ClassCastException("非Student类对象"); 58 Student s = (Student)o; 59 if(this.sum == s.sum) 60 return this.name.compareTo(s.name); 61 else if((this.sum-s.sum)>0) 62 return -1; 63 else if((this.sum-s.sum)<0) 64 return 1; 65 return 0; 66 } 67 @Override 68 public boolean equals(Object o){ 69 if(!(o instanceof Student)) 70 throw new ClassCastException("非Student类对象"); 71 Student s = (Student)o; 72 return this.name.equals(s.name) && this.math==s.math && this.cn == s.cn && this.en == s.en; 73 } 74 @Override 75 public String toString(){ 76 return "student ["+name + "]" + " ,sum = " + sum; 77 } 78 } 79 80 class StudentTool 81 { 82 public static Set<Student> getStudents()throws IOException{ 83 return getStudents(null); 84 } 85 public static Set<Student> getStudents(Comparator cmp)throws IOException{ 86 BufferedReader bufr = new BufferedReader(new InputStreamReader(System.in)); 87 String line = null; 88 Set<Student> stus = null; 89 if(cmp==null) 90 stus = new TreeSet<Student>(); 91 else 92 stus = new TreeSet<Student>(cmp); 93 while((line=bufr.readLine())!=null){ 94 if("done".equals(line)) 95 break; 96 String[] info = line.split(","); 97 Student stu = new Student(info[0],Double.parseDouble(info[1]), 98 Double.parseDouble(info[2]), 99 Double.parseDouble(info[3])); 100 stus.add(stu); 101 } 102 bufr.close(); 103 return stus; 104 } 105 106 public static void write2File(Set<Student> stus,OutputStream out)throws IOException{ 107 BufferedWriter bufw = new BufferedWriter(new OutputStreamWriter(out)); 108 109 for(Student s: stus){ 110 bufw.write(s.toString()); 111 bufw.newLine(); 112 bufw.flush(); 113 } 114 bufw.close(); 115 } 116 }
