IO流

1.用FileInputStream读文件内容，然后再用OutputStream来向文件中写入内容

 1 public class IO1 {
 2     public static void main(String[] args) throws Exception{
 3 
 4         File file=new File("G://ha_xie/a.txt");
 5         InputStream in=new FileInputStream(file);
 6         //读     里面的参数是  从此输入流读取的估计字节数
 7         byte[] b=new byte[in.available()];
 8         in.read(b);
 9         //将字节数组转换成字符串
10         String str=new String(b,0,b.length);
11         System.out.println(str);
12 
13         OutputStream out=new FileOutputStream("G://ha_xie/b.txt");
14         out.write(b);//将数组中的字节写入此输出流
15     }
16 }

2.使用InputStreamReader和OutputStreamWriter

 1 public class IO2 {
 2     public static void main(String[] args)throws Exception {
 3         File file=new File("G://ha_xie/a.txt");
 4         InputStream in=null;
 5         in=new FileInputStream(file);
 6         InputStreamReader is = new InputStreamReader(in);
 7         char[] c=new char[30];
 8         is.read(c);
 9         //字符数组在转换成字符串
10         String str=new String(c);
11         System.out.println(str);
12 //        in.close();
13 //        is.close();
14         //写到c.txt
15         OutputStream out=new FileOutputStream("G://ha_xie/d.txt");
16         OutputStreamWriter os1=new OutputStreamWriter(out);
17         os1.write(str);
18         os1.close();//这个必须关闭，才能向文件里面写入内容
19     }
20 }

3.使用FileReader和FileWriter

 1 public class IO3 {
 2     public static void main(String[] args)throws Exception {
 3         Reader r= new FileReader("G://ha_xie/a.txt");
 4         char[] c=new char[20];
 5         r.read(c);
 6         System.out.println(new String(c));
 7 
 8         Writer w=new FileWriter("G://ha_xie/bb.txt");
 9         w.write(c);
10         w.close();
11     }
12 }

4.使用BufferedReader和BufferedWriter

 1 public class IO4 {
 2     public static void main(String[] args) throws Exception{
 3         //字节流
 4         InputStream in=new FileInputStream("G://ha_xie./a.txt");
 5         //字符流
 6         InputStreamReader r=new InputStreamReader(in);
 7         //缓冲流
 8         Reader reader1=new BufferedReader(new FileReader("G://ha_xie/b.txt"));
 9         Reader reader=new BufferedReader(r);
10         /*String str=((BufferedReader) reader).readLine();//按行读
11         System.out.println(str);*/
12         /*String s;
13         int i=0;
14         while((s=((BufferedReader) reader).readLine())!=null){
15             System.out.println(s);
16             i++;
17         }
18         System.out.println(i);*/
19         String string = ((BufferedReader) reader).readLine();
20         String string2 = ((BufferedReader) reader).readLine();
21         System.out.println(string);
22         System.out.println(string2);
23         //关闭资源
24         reader.close();
25         r.close();
26         in.close();
27         //写
28         BufferedWriter bw=new BufferedWriter(new FileWriter("G://ha_xie/oo.txt"));
29         bw.write("谢军帅谢军帅");
30         bw.newLine();//换行，写入一个行分隔符
31         bw.newLine();
32         bw.write("xiejunshuaixiejunshuai");
33         bw.flush();//刷新
34         bw.close();//关闭此流，但要先刷新它
35     }
36 }
37 //我的理解：是缓冲中的数据，输出一行少一行

注意：使用完流对象之后，要关闭！！！要不然会存在写不进去的情况。