四舍五入至某小数位后返回数字串

 /**
   將數字四捨五入至某小數位, 並返回指定位數字串
   function2(123.455,2) => 123.46
   function2(123.449,2) => 123.45
   function2(123.44,3) => 123.440 
   function2(123.4455,3) => 123.446
   function2(123.4499,3) => 123.450
   function2(123.9,0) => 124
   程式接口:
   public static double function2(double value,int decimalPlaces); */

 

   public static double function2(double value,int decimalPlaces){
       double dbl = value*(Math.pow(10, decimalPlaces+1) );
       Double d = new Double(dbl);
       int intValue = d.intValue();
       intValue+=5;  //四舍五入关键步骤
       intValue = intValue/10; //舍弃最后一位
       int value1 = intValue /((int)Math.pow(10, decimalPlaces));
       int value2 = intValue % ((int)Math.pow(10, decimalPlaces));
       String str = value1+"."+value2;
       if(decimalPlaces==0)str = value1+"";
       System.out.println("str = "+str);
       return Double.parseDouble(str);
   } 
    
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