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：

import java.io.*;
import java.util.*;
public class FileDemo{
    private Formatter f2;
    public void Fileexists(){
        File f1 = new File("D:\test2.txt");
        
        //查看文件test2.txt是否存在
        if(f1.exists())
            System.out.println(f1.getName() + " exists");
        else
            System.out.println("this thing does not exists");
    
    }
    
    
    public void WriteFile(){
        BufferedWriter out = null;
        try{
            out = new BufferedWriter(new FileWriter("fred.txt"));
            out.write("20 sunshineatnoon");
            out.newLine();
            out.write("21 moment");
        }catch(Exception e){
            e.printStackTrace();
        }finally{
            try{
                out.close();
            }catch(Exception e){
                
            }
        }
    }
    
    public void closeFile(){
        f2.close();
    }
    
    //按行读取文件
    public void ReadFile(){
        FileReader reader = null;
        BufferedReader br = null;
        try{
            reader = new FileReader("fred.txt");
            br = new BufferedReader(reader);
            String s1 = null;
            
            while((s1 = br.readLine()) != null){
                System.out.printf("%s
",s1);
            }
            
        }catch(Exception e){
            e.printStackTrace();
        }finally{
            try{
                reader.close();
            }catch(Exception e){
                
            }
        }
    }
}

 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。