java读写文件及保留指定位小数

1）先上代码：

   public  static void main(String[] args)throws IOException{

         double[][] B=new double[1043][21025];
         double[][] transformB=new double[21025][1043];

         String filename="/home/hadoop/srcData/B.txt";
         final LineIterator it = FileUtils.lineIterator(new File(filename), "UTF-8");
         try {
             int i=-1;
             //DecimalFormat df=new DecimalFormat("#.0000");
             while (it.hasNext()) {
                 ++i;
                 final String line = it.nextLine();
                 String[] ele=line.split("\t");
                 for(int j=0;j<ele.length;++j){
                     B[i][j]=Double.valueOf(ele[j]).doubleValue();//String -->double
                     //B[i][j]=Double.valueOf(df.format(B[i][j]) ).doubleValue();
                 }
             }
         } finally {
             it.close();
         }
         //B
          for (int i=0;i<B[0].length;++i)
              for (int j=0;j<B.length;++j){
                  transformB[i][j]=B[j][i];
              }

         String fileName2="/home/hadoop/srcData/transB.txt";
         BufferedWriter w2=new BufferedWriter(new FileWriter(fileName2));
         for (int i=0;i<transformB.length;++i){
             for (int j=0;j<transformB[i].length;++j)
             {
                 w2.write(String.valueOf(transformB[i][j])+"\t");

             }
             if(i!=transformB.length-1)
                 w2.newLine();

         }
         w2.close();

2）读文件，其中直接从文件中读取文件的简洁形式如下，每次读取一行，需要使用commons-io的FileUtils。

 import org.apache.commons.io.FileUtils;
 import org.apache.commons.io.LineIterator;

 final LineIterator it = FileUtils.lineIterator(new File(""), "UTF-8");
 try {
     while (it.hasNext()) {
         final String line = it.nextLine();
     }
 } finally {
     it.close();
 }

3）写文件：

 import java.io.IOException;
 import java.io.FileWriter;
 import  java.io.BufferedWriter;
 String fileName2="/home/hadoop/srcData/transB.txt";
         BufferedWriter w2=new BufferedWriter(new FileWriter(fileName2));
         for (int i=0;i<transformB.length;++i){
             for (int j=0;j<transformB[i].length;++j)
             {
                 w2.write(String.valueOf(transformB[i][j])+"\t");

             }
             if(i!=transformB.length-1)
                 w2.newLine();//插入换行符

         }
         w2.close();

参考：

https://segmentfault.com/q/1010000000359840

http://my.oschina.net/xiangtao/blog/17078

http://glblong.blog.51cto.com/3058613/1312340