Java I/O操作学习笔记

书上写的有点乱，所以就自己总结了一下，主要参考：http://www.cnblogs.com/qianbi/p/3378466.html

1.从文件读出和写入：

 1 import java.io.*;
 2 import java.util.*;
 3 public class FileDemo{
 4     private Formatter f2;
 5     public void Fileexists(){
 6         File f1 = new File("D:\test2.txt");
 7         
 8         //查看文件test2.txt是否存在
 9         if(f1.exists())
10             System.out.println(f1.getName() + " exists");
11         else
12             System.out.println("this thing does not exists");
13     
14     }
15     
16     
17     public void WriteFile(){
18         BufferedWriter out = null;
19         try{
20             out = new BufferedWriter(new FileWriter("fred.txt"));
21             out.write("20 sunshineatnoon");
22             out.newLine();
23             out.write("21 moment");
24         }catch(Exception e){
25             e.printStackTrace();
26         }finally{
27             try{
28                 out.close();
29             }catch(Exception e){
30                 
31             }
32         }
33     }
34     
35     public void closeFile(){
36         f2.close();
37     }
38     
39     //按行读取文件
40     public void ReadFile(){
41         FileReader reader = null;
42         BufferedReader br = null;
43         try{
44             reader = new FileReader("fred.txt");
45             br = new BufferedReader(reader);
46             String s1 = null;
47             
48             while((s1 = br.readLine()) != null){
49                 System.out.printf("%s
",s1);
50             }
51             
52         }catch(Exception e){
53             e.printStackTrace();
54         }finally{
55             try{
56                 reader.close();
57             }catch(Exception e){
58                 
59             }
60         }
61     }
62 }

2.从控制台输入

public void ReadFromConsle(){
    Scanner sc = new Scanner(System.in);
    System.out.println("输入数字:");
    System.out.println("输入的数字为："+sc.nextInt());
    
    System.out.println("输入字符串：");
    System.out.println("输入的字符串为："+sc.next());
}

类似的还有sc.nextDouble()等，如果不知道什么输入，直接按照字符串处理。