Java：指定小数点后面的数字

Question

我有一个用于计算数据范围的GUI Java代码，例如，如果两个值输入2.444和3.555，结果将是一个长双1.11100000...等。如何指定它应显示的小数点后面的位数？ （例如：%.2f）

这是我的代码：

public class Range
{
    public static void main(String args[])
    {
        int num=0; //number of data
        double d; //the data
        double smallest = Integer.MAX_VALUE;
        double largest = Integer.MIN_VALUE;
        double range = 0;

        String Num =
        JOptionPane.showInputDialog("Enter the number of data ");
        num=Integer.parseInt(Num);

        for(int i=0; i<num; i++)    
        {
            String D =
            JOptionPane.showInputDialog("Enter the data ");
            d=Double.parseDouble(D);

            if(d < smallest)
                smallest = d;
            if(d > largest)
                largest = d; 
        }

        range = largest - smallest ; //calculating the range of the input

        JOptionPane.showMessageDialog(null,"Range = "+smallest+"-"+largest+" = "+range,"Range",JOptionPane.PLAIN_MESSAGE);
    }
}

Answer 1

您可以使用String.format定义您喜欢的输出，例如

String.format("Range = %.4f", range)

显示4位小数。

Answer 2

DecimalFormat。下面的例子形式here

import java.text.DecimalFormat;
import java.text.NumberFormat;

public class DecimalFormatExample
{
    public static void main(String[] args)
    {
        // We have some millons money here that we'll format its look.
        double money = 100550000.75;

        // By default to toString() method of the Double data type will print
        // the money value using a scientific number format as it is greater
        // than 10^7 (10,000,000.00). To be able to display the number without
        // scientific number format we can use java.text.DecimalFormat wich
        // is a sub class of java.text.NumberFormat.

        // Below we create a formatter with a pattern of #0.00. The # symbol
        // means any number but leading zero will not be displayed. The 0 
        // symbol will display the remaining digit and will display as zero
        // if no digit is available.
        NumberFormat formatter = new DecimalFormat("#0.00");

        // Print the number using scientific number format.
        System.out.println(money);

        // Print the number using our defined decimal format pattern as above.
        System.out.println(formatter.format(money));
    }
}

Answer 3

用这个：

double x = new Random.nextDouble(); //ex: x = 0.126521478419346598
x = Math.round(x*1000)/1000.0;  //x will be: 0.126

Answer 4

将此DecimalFormat实例添加到方法的顶部：

DecimalFormat three = new DecimalFormat("0.000");

// or this. this will modify the number to have commas every new thousandths place.
DecimalFormat three = new DecimalFormat("#,##0.000");

// the three zeros after the decimal point above specify how many decimal places to be accurate to.
// the zero to the left of the decimal place above makes it so that numbers that start with "0." will display "0." vs just "." If you don't want the "0.", replace that 0 to the left of the decimal point with "#"

然后，调用此实例并在显示时传递一个字符串：

String str = 4.651681351;
display.setText(three.format(str)); // displays 4.652