Java Exercises: Create the first twenty Hamming numbers

Java Numbers: Exercise-27 with Solution

Write a Java program to create the first twenty Hamming numbers.

Pictorial Presentation:

Java: Print the Create the first twenty Hamming numbers

In computer science, regular numbers are often called Hamming numbers, Hamming Numbers are numbers whose only prime factors are 2, 3 and 5.
The first few hamming numbers are :
1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, 16, 18, 20, 24, 25, 27, 30, 32

Sample Solution:

Java Code:

// https://rosettacode.org/
import java.math.BigInteger; 
public class Exercise28 {

    public static void main(String args[])
        Stream hamming = makeHamming();
        System.out.print("First Twenty Hamming numbers: ");
        for (int i=0; i<20; i++) {
            System.out.print(" ");
            hamming = hamming.advance();
    public interface Stream
        BigInteger value();
        Stream advance();
    public static class MultStream implements Stream
        MultStream(int mult)
        { m_mult = BigInteger.valueOf(mult); }
        MultStream setBase(Stream s)
        { m_base = s; return this; }
        public BigInteger value()
        { return m_mult.multiply(m_base.value()); }
        public Stream advance()
        { return setBase(m_base.advance()); }
        private final BigInteger m_mult;
        private Stream m_base;
    private final static class RegularStream implements Stream
        RegularStream(Stream[] streams, BigInteger val)
            m_streams = streams;
            m_val = val;
        public BigInteger value()
        { return m_val; }
        public Stream advance()
            // memoized value for the next stream instance.
            if (m_advance != null) { return m_advance; }
            int minidx = 0 ;
            BigInteger next = nextStreamValue(0);
            for (int i=1; i<m_streams.length; i++) {
                BigInteger v = nextStreamValue(i);
                if (v.compareTo(next) < 0) {
                    next = v;
                    minidx = i;
            RegularStream ret = new RegularStream(m_streams, next);
            // memoize the value!
            m_advance = ret;
            return ret;
        private BigInteger nextStreamValue(int streamidx)
            // skip past duplicates in the streams we're merging.
            BigInteger ret = m_streams[streamidx].value();
            while (ret.equals(m_val)) {
                m_streams[streamidx] = m_streams[streamidx].advance();
                ret = m_streams[streamidx].value();
            return ret;
        private final Stream[] m_streams;
        private final BigInteger m_val;
        private RegularStream m_advance = null;
    private final static Stream makeHamming()
        MultStream nums[] = new MultStream[] {
            new MultStream(2),
            new MultStream(3),
            new MultStream(5)
        Stream ret = new RegularStream(nums, BigInteger.ONE);
        for (int i=0; i<nums.length; i++) {
        return ret;

Sample Output:

First Twenty Hamming numbers: 1 2 3 4 5 6 8 9 10 12 15 16 18 20 24 25 27 30 32 36


Flowchart: Create the first twenty Hamming numbers

interface Stream :

Flowchart: Create the first twenty Hamming numbers

MultStream implements Stream :

Flowchart: Create the first twenty Hamming numbers

RegularStream implements Stream :

Flowchart: Create the first twenty Hamming numbers

Stream makeHamming :

Flowchart: Create the first twenty Hamming numbers

Java Code Editor:

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Previous: Write a Program in Java to check whether a number is a Keith Number or not.
Next: Write a Program in Java to check whether a number is an Armstrong Number 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