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