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Java Exercises: Check whether a number is a Duck Number or not

Java Numbers: Exercise-15 with Solution

Write a Java program to check whether a number is a Duck Number or not.

Note: A Duck number is a number which has zeroes present in it, but there should be no zero present in the beginning of the number. For example 3210, 7056, 8430709 are all duck numbers whereas 08237, 04309 are not.

Test Data
Input a number : 3210

Pictorial Presentation:

Java: Check whether a number is a Duck Number or not.

Sample Solution:

Java Code:

import java.util.Scanner;

public class Example15  {

    public static void main(String args[])
       {
        Scanner sc = new Scanner(System.in);
        System.out.print("Input a number : ");
        String nstr = sc.nextLine();
 
        int l = nstr.length();  
        int ctr = 0;  
        char chr;
 
        for(int i=1;i<l;i++)
        {
            chr = nstr.charAt(i); 
            if(chr=='0')
                ctr++;
        }
 
        char f = nstr.charAt(0); 
 
        if(ctr>0 && f!='0')
            System.out.println("Duck number");
        else
            System.out.println("Not a duck number");
    }
}

Sample Output:

Input a number : 3210                                                                                         
Duck number

Flowchart:

Flowchart: Check whether a number is a Duck Number or not

Java Code Editor:

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Previous: Write a Java program check whether a number is an Automorphic number or not.
Next: Write a Java program to check two numbers are Amicable numbers or not.

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Java: Tips of the Day

Array vs ArrayLists:

The main difference between these two is that an Array is of fixed size so once you have created an Array you cannot change it but the ArrayList is not of fixed size. You can create instances of ArrayLists without specifying its size. So if you create such instances of an ArrayList without specifying its size Java will create an instance of an ArrayList of default size.

Once an ArrayList is full it re-sizes itself. In fact, an ArrayList is internally supported by an array. So when an ArrayList is resized it will slow down its performance a bit as the contents of the old Array must be copied to a new Array.

At the same time, it's compulsory to specify the size of an Array directly or indirectly while creating it. And also Arrays can store both primitives and objects while ArrayLists only can store objects.

Ref: https://bit.ly/3o8L2KH