BP Forums - Java

Character ammount

Mon, 25 Apr 2016 14:32:40 +0000

I've just finished watching your tenth "Learning Java" part and I want to limit the character number to five digits only.Â
I've tried this:

Code:
import java.util.*;

public class digitExtractorTester {

    static Scanner userInput = new Scanner(System.in);

    public static void main(String[] args){

        String rNumber = "12345";

        System.out.print("Enter a custom, five digit number: ");

        String nSequence = userInput.next();

        System.out.println(" ");

        if (nSequence.chars() != rNumber.chars()){

            System.out.println("Your input contains too many or too less digits.\nOnly five digit numbers are allowed.");

        }

        else{

        digitExtractor byMath = new digitExtractor(Integer.valueOf(nSequence));

        byMath.returnNumberSequenceByMath();

        System.out.println(" ");

        digitExtractor byChar = new digitExtractor(nSequence);

        byChar.returnNumberSequenceByChar();

        }

    }

}

But it doesn't seem to be working. Any suggestions?

Never mind. I solved my own problem.
If anyone's wondering, I was using chars() when I was supposed to be using length(). (Source of information)

Code:
nSequence.length() != rNumber.length()

Adding backgroundcolor to snake applet

Fri, 28 Aug 2015 16:51:31 +0000

Hi guys,

first, i'm not the best english speaker and -writer. Therefore i ask you to apologize my language mistakes

Problably in your eyes, i have a very simply problem, but i cant add the background function to Brandonio's Snake Project. I want to have a black background in the applet. After this, i want to change the color of the grid to white.

I try to add two JPanel's to snakeApplet.java. But is it still not working. Every time i started the Applet, the background is white.

Code:
import java.applet.Applet;

import java.awt.BorderLayout;

import java.awt.Color;

import java.awt.Dimension;

import java.awt.Graphics;

import javax.swing.JPanel;

public class snakeApplet extends Applet{

    private snakeCanvas c;

    JPanel jp1 = new JPanel();

    JPanel jp2 = new JPanel();

    public void init()

    {

        jp1.setBackground(Color.BLACK);

        add(jp1);

        jp2.setBackground(Color.BLACK);

        add(jp2, BorderLayout.SOUTH);

        c = new snakeCanvas();

        c.setSize(new Dimension(640, 480));

        c.setPreferredSize(new Dimension(640, 480));

        c.setVisible(true);

        c.setFocusable(true);

        this.add(c);

        this.setVisible(true);

        this.setSize(new Dimension(640, 480));

    }

    public void paint(Graphics g)

    {

        this.setSize(new Dimension(640, 480));

    }

}

In addition, i want to add music to the applet. The music should instantly playing if the applet is open.
If the idea of the black background and white grid is not to be a looker, than i would to add a picture in the background of the grid.
But i dont know how i can code it.
I hope someone can help me please
Yours sincerley
Kevin

Edit: Kevin is only a nickname

Knuth Numbers recursion

Wed, 22 Apr 2015 07:46:17 +0000

Hello,

I recently had a final exam on which my teacher asked to write a method for Knuth numbers recursion. I got a stack overflow on my implementation, and I am new on Java, so I am not sure what happened, it might be that I had the wrong formula for Knuth numbers? I would love some feedback.

Here is the question, and my code

Knuth numbers are given by the recursive formula Kn+1 = 1 + min (2 * Ka, 3 * Kb) where a is the smallest integer larger than n/2.0 and b is the smallest integer larger than n/3.0. The use of doubles in the denominator is necessary to ensure that integer division is not used.

For example, if n is 7, then a equals 4 and b equals 3 and thus K8 = 1 + min (2* K4, 3 * K3).

If n is 8, then a equals 5 while b remains 3 and thus K9 = 1 + min (2 * K5, 3 * K3).
If n is 9, then a remains 5 while b equals 4 and thus K10 = 1 + min(2 * K5, 3 * K3).

Mathematically, â€œthe smallest integer larger than xâ€ is the â€œceilingâ€ function. If n is an int, then n / 2 is calculated using integer division, discarding the remainder; but you want the division to give you a double. Thus you need code that looks like this:

int a = Math.ceil(n / 2.0);
int b = Math.ceil(n / 3.0);

Since the equation defining Knuth numbers is a recursive one, we must have a base case; letâ€™s assume that K0 = 1.

Create and test a class called KnuthNumbers (in a project also called KnuthNumbers) which includes a static method to compute Knuth numbers.

my code:

Code:
public class KnuthNumbers

{

Â  Â /**

Â  Â  * Recursive Knuth Numbers 1, 3, 3, 4, 7, 7, 7, 9, 9, 10, 13, ... Â 

Â  Â  */

Â  Â public static int knuthNumber(final double n)

Â  Â throws DataFormatException{

Â  Â  Â  Â double a = Math.ceil(n / 2.0);

Â  Â  Â  Â double b = Math.ceil(n / 3.0);

Â  Â  Â  Â // bad input

Â  Â  Â  Â if (n < 1)

Â  Â  Â  Â  Â  Â throw new DataFormatException("n cannot be less then 1");

Â  Â  Â  Â if (n > 12)

Â  Â  Â  Â  Â  Â throw new DataFormatException("n is too large. Max is 12");

Â  Â  Â  Â //base case

Â  Â  Â  Â if (n == 1)

Â  Â  Â  Â  Â  Â return 1;

Â  Â  Â  Â //recursion

Â  Â  Â  Â return knuthNumber(a + b);

Â  Â }

}

TEST:

Code:
public class KnuthNumbersTest

{

Â  Â  

Â  Â @Test

Â  Â public void testKnuthNumber(){

Â  Â  Â  Â long startTime = 0;

Â  Â  Â  Â long endTime = 0;

Â  Â  Â  Â double result = 0;

Â  Â  Â  Â try {

Â  Â  Â  Â  Â  Â assertEquals(-1, KnuthNumbers.knuthNumber(-3));

Â  Â  Â  Â  Â  Â fail("number should not be negative");

Â  Â  Â  Â }

Â  Â  Â  Â catch (DataFormatException e){

Â  Â  Â  Â  Â  Â assertEquals("n cannot be less then 1", e.getMessage());

Â  Â  Â  Â }

Â  Â  Â  Â catch (Exception e) {

Â  Â  Â  Â  Â  Â fail("Unexpected exception: " + e.toString());

Â  Â  Â  Â }

Â  Â  Â  Â try {

Â  Â  Â  Â  Â  Â assertEquals(0, KnuthNumbers.knuthNumber(0));

Â  Â  Â  Â  Â  Â fail("number should not be zero");

Â  Â  Â  Â }

Â  Â  Â  Â catch (DataFormatException e){

Â  Â  Â  Â  Â  Â assertEquals("n cannot be less then 1", e.getMessage());

Â  Â  Â  Â }

Â  Â  Â  Â catch (Exception e) {

Â  Â  Â  Â  Â  Â fail("Unexpected exception: " + e.toString());

Â  Â  Â  Â }

Â  Â  Â  Â try {

Â  Â  Â  Â  Â  Â assertEquals(1, KnuthNumbers.knuthNumber(1.0));

Â  Â  Â  Â  Â  Â assertEquals(9, KnuthNumbers.knuthNumber(5.4));

Â  Â  Â  Â  Â  Â assertEquals(13, KnuthNumbers.knuthNumber(7.6));

Â  Â  Â  Â }

Â  Â  Â  Â catch (Exception e) {

Â  Â  Â  Â  Â  Â fail ("Unexpected exception: " + e.toString());

Â  Â  Â  Â }

Â  Â }

}