java System.out、System.setIn

//可以向文件里写数据

import java.io.FileNotFoundException;

import java.io.PrintStream;

public class TestPrintStream1 {

public static void main(String[] args) {

try {

PrintStream out = System.out;

PrintStream ps = new PrintStream("./log.txt");

System.setOut(ps);

int age = 11;

System.out.println("年龄变量成功定义，初始值为11");

String sex = "女";

System.out.println("年龄变量成功定义，初始值为女");

// 整合2个变量

String info = "这是个" + sex + "孩子，应该有" + age + "岁了";

System.setOut(out);

System.out.println("程序运行完毕，请查看日志");

} catch (FileNotFoundException e) {

e.printStackTrace();

}

}

import java.io.InputStream;

import java.io.FileInputStream;

import java.io.FileNotFoundException;

import java.util.Scanner;

public class TestPrintStream1 {

public static void main(String[] args) {

try {

InputStream in = System.in;

InputStream ps = new FileInputStream("./log.txt");

System.setIn(ps);

Scanner scanner = new Scanner(System.in);

String line = "";

while (scanner.hasNextLine()) {

line = scanner.nextLine();

System.out.println(line);

}

} catch (FileNotFoundException e) {

e.printStackTrace();

}

}

}

原文：

http://blog.csdn.net/xiao472613694/article/details/7313657