程序代码：

import java.text.DecimalFormat;


 public class hjj {
    public static void main(String[] args) {
                DecimalFormat df = new DecimalFormat( "0.0000 ");
                double d1 = 1.0;
                double d2 = 4.56789;
                System.out.println(df.format(d1)); 
                System.out.println(df.format(d2)); 
         }

 } 

算是找到了