Java: nextDouble get numbers from user message doesn't get printed

My output is:

Enter dog sizes or END to end: 1
2
3
4
END
Total dog sizes: 10.0

Why I need it to be

Enter dog sizes or END to end: 1
Enter dog sizes or END to end: 2 3
Enter dog sizes or END to end: 4
Enter dog sizes or END to end: END
Total dog sizes: 10.0

import java.util.Scanner;

public class Test3 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        double total = 0;

        do {
            System.out.print("Enter dog sizes or END to end: ");

            while (scanner.hasNextDouble()) {
                total += scanner.nextDouble();
            }
            scanner.nextLine();

            String q = scanner.nextLine();
            if (q.equals("END")) {
                break;
            }
        } while (true);

        System.out.println("Total dog sizes: " + total);

    }
}

The message is not being printed simply because you don't print it after reading the next double in your code. You can enter the print statement in your while loop to re-print the message like you describe:

while (scanner.hasNextDouble()) {
    total += scanner.nextDouble();
    System.out.print("Enter dog sizes or END to end: ");
}

EDIT:

Your parent do..while loop only gets executed once, so the message will only get printed once. If you want it printed on every line then you can do this:

Scanner scanner = new Scanner(System.in);
double total = 0;

do {
	System.out.print("Enter dog sizes or END to end: ");
    String q = scanner.nextLine();		        
	try {
        String[] str = q.split("\\s+");
		for(String s: str) {
		    total += Double.parseDouble(s);
	    }
	}catch(NumberFormatException e) {   //invalid double
	    if(q.toUpperCase().equals("END")) {
	        break;  //stop if END or end is entered
	}               
	    continue;   //skip over other invalid doubles
	}
       
} while(true);

System.out.println("Total dog sizes: " + total);

I read a whole line, and then split the numbers at white spaces.

Perhaps you should do it this way (read the comments in code):

Scanner scanner = new Scanner(System.in);
double total = 0;
String dogSizeStrg = "";
while (dogSizeStrg.isEmpty()) {
    System.out.print("Enter dog sizes or END to end: ");
    dogSizeStrg = scanner.nextLine().trim();
    if (dogSizeStrg.equalsIgnoreCase("end")) {
        break;
    }
    // Is the entered numerical value a signed or 
    // unsigned Integer or floating point number?
    if (dogSizeStrg.matches("-?\\d+(\\.\\d+)?")) {
        // Yes...it is.
        total+= Double.valueOf(dogSizeStrg); // Convert to double and add to total.
    }
    else {
        // No... it isn't so inform User and let
        // him/her try again.
        System.err.println("Invalid numerical value supplied! (" + 
                           dogSizeStrg + ") Try Again...");
    }
    dogSizeStrg = ""; // Reset to loop again...
} 

System.out.println("Total dog sizes: " + total);

The Scanner#nextLine() method is used here along with the String#matches() method and a Regular Expression (RegEx) to validate that a signed or unsigned Integer or floating point value was supplied.

You have input separated by space, so you have to use nextLine().split(“ ”) as shown below and get your desired output:

public class Test3 
{
    public static void main(String[] args) 
    {
        Scanner scanner = new Scanner(System.in);
        double total = 0;
        String q = "";
        do 
        {
            System.out.print("Enter dog sizes or END to end: ");

            if(scanner.hasNextDouble())
            {
               String s[]= scanner.nextLine().split(" ");
               for(int i =0 ;i < s.length;i++)
                     total+= Double.parseDouble(s[i]);
            }      
            else
            {
               q = scanner.nextLine();
            }          
        } while (!q.equals("END"));
        
        scanner.close();
        System.out.println("Total dog sizes: " + total);
    }
}

Do it as follows:

import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
double total = 0;
do {
System.out.print("Enter dog sizes or END to end: ");
String q = scanner.nextLine();
// Create a new Scanner with the input string
Scanner doubles = new Scanner(q);
while (doubles.hasNextDouble()) {
total += doubles.nextDouble();
}
if (q.equals("END")) {
break;
}
} while (true);
System.out.println("Total dog sizes: " + total);
}
}

A sample run:

Enter dog sizes or END to end: 1
Enter dog sizes or END to end: 2 3
Enter dog sizes or END to end: 4
Enter dog sizes or END to end: 5
Enter dog sizes or END to end: END
Total dog sizes: 15.0

Also, note that when you use a condition inside an infinite loop to break it, you can simply use while (true) {//...} instead of do {//...} while(true); e.g. the following code will behave in the same way as the above one.

import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
double total = 0;
while (true) {
System.out.print("Enter dog sizes or END to end: ");
String q = scanner.nextLine();
// Create a new Scanner with the input string
Scanner doubles = new Scanner(q);
while (doubles.hasNextDouble()) {
total += doubles.nextDouble();
}
if (q.equals("END")) {
break;
}
}
System.out.println("Total dog sizes: " + total);
}
}