流---是指的一組有序的、有氣墊和重點的字節集合，是對的護具傳輸的總稱或者抽象。

流采用緩沖區技術，當寫一個數據時，系統將數據發送到緩沖區而不是外部設備（如硬盤），當讀一個數據時，系統實際是從緩沖區讀取數據的。

流的存在：我們都知道輸入流和輸出流，二者的定義都是基於數據流向且是以內存為坐標的。標準輸入過程中，數據從鍵盤等輸入設備流向內存，這事輸入流。標準輸出過程中，數據從內存輸出到顯示器或者打印機等設備，這是輸出流。

流分為字節流和字符流

下邊主要講標準輸入輸出、文件字節流、數據字節流和對象字節流四種字節流。

  1 public class IOtest {
  2     
  3     public
 
 static void main(String[] args) throws IOException {
  4         
  5 //        KeyboardInput();
  6         
  7 //        byte[] buffer = {0,1,2,3,4,5,6,7,8,9};
  8 //        ByteFile afile = new ByteFile("info.txt");
  9 //        afile.writeToFile(buffer);
 10 //        afile.readFromFile();
 11 //        afile.copyFile("io2.txt");
 
 12         
 13 //        IntFile afile = new IntFile("fileInt.txt");
 14 //        afile.writeToFile();
 15 //        afile.readFromFile();
 16         
 17         Student stus[] = {new Student("張三", "男"), new Student("李四", "女"), new Student("王五", "女博士")};
 18         objectFile afile = new objectFile("students.dat");
 
 19         afile.writeToFile(stus);
 20         System.out.println("stus: \n" + afile.readFromFile());
 21     }
 22     
 23     //標準輸入輸出
 24     public static void KeyboardInput() throws IOException{
 25         System.out.print("Input:");
 26         byte buffer[] = new byte[512];    //以字節數組作為緩沖區
 27         int count = System.in.read(buffer);
 28         System.out.print("Output:");
 29         for(int i=0; i<count; i++){
 30             System.out.print(" " + buffer[i]);
 31         }
 32         System.out.println("\ncount = " + count);
 33         for(int i=0; i<count; i++){
 34             System.out.print((char)buffer[i]);
 35         }
 36     }
 37     
 38     //文件字節流
 39     static class ByteFile{
 40         public String filename;
 41         public ByteFile(String filename){
 42             this.filename = filename;
 43         }
 44         //字節流寫
 45         public void writeToFile(byte[] buffer) throws IOException{
 46             FileOutputStream fout = new FileOutputStream(this.filename);
 47             fout.write(buffer);
 48             fout.close();
 49         }
 50         //字節流讀
 51         public void readFromFile() throws IOException{
 52             FileInputStream fin = new FileInputStream(this.filename);
 53             System.out.print(this.filename + ":");
 54             byte[] buffer = new byte[512];
 55             int count=0;
 56             while(count != -1){
 57                 count = fin.read(buffer);           //read返回值為字節數目，當為空時 返回-1
 58                 for(int i=0; i<count; i++){
 59                     System.out.print(buffer[i] + " ");
 60                 }
 61                 System.out.println(" count = " + count);
 62             }
 63             fin.close();
 64         }
 65         //文件字節流復制到filename2
 66         public void copyFile(String filename2) throws IOException{
 67             FileInputStream fin = new FileInputStream(this.filename);
 68             FileOutputStream fout = new FileOutputStream(filename2);
 69             byte[] buffer = new byte[512];
 70             int count = fin.read(buffer);                //讀取輸入流並返回流的大小
 71             while(count != -1){
 72                 fout.write(buffer, 0, count);
 73                 count = fin.read(buffer);
 74             }
 75             fin.close();
 76             fout.close();
 77             System.out.println("Copy file from " + this.filename + " to " + filename2);
 78         }
 79     }
 80     
 81     //數據字節流(舉例 整形)
 82     //把fibonacci序列值寫入指定文件
 83     static class IntFile{
 84         public String filename;
 85         public IntFile(String filename){
 86             this.filename = filename;
 87         }
 88         public void writeToFile() throws IOException{                   
 89             
 90             FileOutputStream fout = new FileOutputStream(this.filename);
 91             DataOutputStream dout = new DataOutputStream(fout);
 92             short i=0,j=1;
 93             do{
 94                 dout.writeInt(i);
 95                 dout.writeInt(j);
 96                 i = (short)(i+j);
 97                 j = (short)(i+j);
 98             }while(i>0);
 99             dout.close();
100             fout.close();
101         }
102         public void readFromFile() throws IOException{
103             FileInputStream fin = new FileInputStream(this.filename);
104             DataInputStream din = new DataInputStream(fin);
105             System.out.println(this.filename + ": ");
106             while(true){
107                 try {
108                     int i = din.readInt();
109                     System.out.print(i + " ");
110                 } catch (Exception e) {
111                     break;
112                 }
113             }
114             din.close();
115             fin.close();
116         }
117     }
118     
119     //對象字節流
120     //使用對象字節流讀寫多個學生對象到某個指定文件
121     static class objectFile{
122         String filename;
123         public objectFile(String filename){
124             this.filename = filename;
125         }
126         
127         public void writeToFile(Object[] objs) throws IOException{
128             FileOutputStream fout = new FileOutputStream(this.filename);
129             ObjectOutputStream obout = new ObjectOutputStream(fout);
130             for(int i = 0; i<objs.length; i++){
131                 obout.writeObject(objs[i]);
132             }
133             obout.close();
134             fout.close();
135         }
136         
137         public String readFromFile() throws IOException{
138             FileInputStream fin = new FileInputStream(this.filename);
139             ObjectInputStream obin = new ObjectInputStream(fin);
140             System.out.println(this.filename + ": ");
141             String str = "";
142             while(true){
143                 try {
144                     str += obin.readObject().toString() + "\n";
145                 } catch (Exception e) {
146                     break;
147                 }
148             }
149             obin.close();
150             fin.close();
151             return str;
152         }
153     }
154     public static class Student implements Serializable{//內部類 學生對象
155 
156         private String name;
157         private String sex;
158         public Student(String name, String sex){
159             this.name = name;
160             this.sex = sex;
161         }
162         public String toString(){
163             return "姓名： " + this.name + "    性別： " + this.sex;
164         }
165      }
166 }

javaIO--字節流