Thread: how to format double value?

here is waht I'm tring to do:

A household is preparing its next month's budget. For this, they want to estimate their monthly grocery spend. They expect their next month's grocery spend to be 10% higher than the average spend over the last several months. Given their grocery spend for the last several months, the expected spend should be rounded off to 2 decimal places. For e.g. if the input is {1004.56,1200,989.50,1100,1050.36,1000.88,1104.56, 990,1089.50,1070,1310.36,900.88}, the expected output is 1174.31

and coding done by me

import java.text.DecimalFormat;
public class GroceryPlan {
	static double[] test1 = {1004.56,1200,989.50,1100,1050.36,1000.88,1104.56,990,1089.50,1070,1310.36,900.88};
 
	static double[] testcase = test1;
 
	public static void main(String args[]){
		GroceryPlan inst = new GroceryPlan();
		double v = inst.getEstimate(testcase);
		System.out.println(v);
	}
 
	// Write your code in the function below
	public double getEstimate(double[] spends){
	         double total=0,inc=0;
	         DecimalFormat Form = new DecimalFormat("#.##");
	         double count= spends.length;
	         for(double element:spends){
		        total+=element;
		       }
	         System.out.printf("total amount : %.2f\n",total);
	         System.out.println("Months :"+count);
	         total/=count;
	         inc=total*0.1;
	         total+=inc;
	         return Double.valueOf(Form.format(total));
	}

output is looking fine but look here when code is check for quality
execution.JPG

Please guide me how to format double values? please look at the screen shot

output is looking fine but look here when code is check for quality

First to explain what is going on...

"Formatting" is the process of going from a numeric quantity to a string. In themselves double values don't have decimal places (or a base for that matter): they just have magnitude. Once they are formatted - ie a string is obtained - then we can talk about decimal places. In your code the format() method does this. It goes from a double to a String.

"Parsing" is the opposite of formatting. It starts with a string and obtains a double. It takes some getting used to, but "3.14159" and 3.14159 are just different things. In particular the former has decimal places, the latter (considered as a double) does not. Parsing has to make a guess (or be told) about the base, but the information about the number of decimal places is lost. In your code the valueOf() method does the parsing.

Your code formats the double total to obtain a string with two decimal places. But then it parses that string to obtain a double from which all information about decimal places is lost. Hence when your main() method prints the double it received you get more decimal places than you intended. (println(), unlike printf(), uses a default formatting which is wider than you want.)

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What is the getEstimate() method supposed to do?

I ask because the name suggests it calculates the estimate, but you have it doing other things (formatting to create a string, printing that string.) I suggest you read whatever instructions came with the exercise and don't try and do more in this method than you have to.

Secondly, the method returns a double. Not a String. The reasons given before would indicate that this getEstimate() method is not the place to be doing the formatting. (formatting can only make numeric values less accurate). If getEstimate() is supposed to return a double, then let it return that double and have main() do the formatting. If getEstimate() itself is supposed to do the formatting, then there is no choice: it should return a String, not a double. The instructions should make it clear which is intended.

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[Edit] I realise I didn't address the "please guide me" part of your post. You already know how to format numeric quantities - in fact your code illustrates two different methods of doing that.