IO流java.util.Scanner

从键盘读取

import java.util.Scanner;

public class Demo {

    public static void main(String[] args ) {

        Scanner input = new Scanner(System.in);    

        System.out.println("请输出一个整数：");

        int i = input.nextInt();

        System.out.println("你输入的整数是：" + i);

    }

}

从字符串读取

import java.util.Scanner;

public class Demo {

    public static void main(String[] args ) {

        //这里的\r\n是换行符，Linux下其实只用\n即可

        Scanner input = new Scanner("hello\r\nworld\r\n");

        //循环读取，hasNext()方法和集合框架里面的一样使

        while(input.hasNext()) {

            //每次读取一行，别的读取方法见API，比较简单

            String s = input.nextLine();

            System.out.println(s);

        }  

    }

}

从文件读取

import java.io.File;

import java.io.FileNotFoundException;

import java.util.Scanner;

public class Demo {

    public static void main(String[] args ) {

        String path = File.separator + "home" + File.separator + "siu" +

                      File.separator + "work" + File.separator + "demo.txt";

        File f = new File(path);

        Scanner input = null;

        try {

            //从文件构造Scanner对象，有可能产生异常

            input = new Scanner(f);

            while(input.hasNext()) {

                String s = input.nextLine();

                System.out.println(s);

            }

        } catch (FileNotFoundException e) {

            e.printStackTrace();

        } finally {

            input.close();

        }  

    }

}