[20160730]while 条件的死循环和正常循环对比

正常循环

 import java.io.*;
 import java.util.*;

 public class MyPrintStreamTest3{
   public static void main(String[] args) {
     BufferedReader br = new BufferedReader(  new InputStreamReader(System.in) );
     String s = null;

   try
   {
     PrintWriter log = new PrintWriter( new FileWriter("D://javalearning//MYIO//log4j.txt",true) );
     while((s = br.readLine())!=null){
       if (s.equalsIgnoreCase("exit")) break;
        System.out.println(s.toUpperCase());
        log.println("--------");
        log.println(s.toUpperCase());
        log.flush();
     }
     log.println("=="+new Date()+"==");
     log.flush();
     log.close();

   }
   catch (IOException e)
   {
      e.printStackTrace();
   }
 }
 }

死循环

 import java.io.*;
 import java.util.*;

 public class MyPrintStreamTest3{
   public static void main(String[] args) {
     BufferedReader br = new BufferedReader(  new InputStreamReader(System.in) );
     String s = null;

   try
   {
     PrintWriter log = new PrintWriter( new FileWriter("D://javalearning//MYIO//log4j.txt",true) );
     s = br.readLine();
     while(s!=null){
       if (s.equalsIgnoreCase("exit")) break;
        System.out.println(s.toUpperCase());
        log.println("--------");
        log.println(s.toUpperCase());
        log.flush();
     }
     log.println("=="+new Date()+"==");
     log.flush();
     log.close();

   }
   catch (IOException e)
   {
      e.printStackTrace();
   }
 }
 }