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("	");
                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])+"	");

            }
            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])+"	");

            }
            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