java从文本文件中添加值

Question

大家好，我有一个文本文件，包含每行子字符串（34，47）处的金额。我需要将所有值汇总到文件末尾。我有一个我已经开始构建的代码，但我不知道如何从这里开始：

public class Addup {

/**
 * @param args the command line arguments
 */
public static void main(String[] args) throws FileNotFoundException, IOException {
    // TODO code application logic here
    FileInputStream fs = new FileInputStream("C:/Analysis/RL004.TXT");
    BufferedReader br = new BufferedReader(new InputStreamReader(fs));
    String line;
    while((line = br.readLine()) != null){
        String num = line.substring(34, 47);

        double i = Double.parseDouble(num);
        System.out.println(i);
    }
}
}

输出如下：

1.44576457E4
2.33434354E6
4.56875685E3

金额在小数点后两位，我需要结果也在小数点后两位。实现这一目标的最佳方式是什么

Answer 1

或者，使用String.format格式化双精度值

System.out.println (String.format("%1.2f", i));

Answer 2

DecimalFormat是最好的选择：

double roundTwoDecimals(double d) {
            DecimalFormat twoDForm = new DecimalFormat("#.##");
        return Double.valueOf(twoDForm.format(d));
}

您可以将代码更改为：

public static void main(String[] args) throws FileNotFoundException, IOException {
    // TODO code application logic here
    double sum = 0.0;
    FileInputStream fs = new FileInputStream("C:/Analysis/RL004.TXT");
    BufferedReader br = new BufferedReader(new InputStreamReader(fs));
    String line;
    while((line = br.readLine()) != null){
        String num = line.substring(34, 47);

        double i = Double.parseDouble(num);
        sum = sum + i;
        DecimalFormat twoDForm = new DecimalFormat("#.##");
        System.out.println(Double.valueOf(twoDForm.format(i)));
    }
        System.out.println("SUM = " + Double.valueOf(twoDForm.format(sum)));
}
}