Develop Reference

Can't use toString to display array

getting the following error message when trying to use toString to display array:
java.lang.NullPointerException
Here's the code:
import java.util.Scanner;
import java.util.Random;
public class RandomArray {
private int data[];
private int value;
public RandomArray(int x)
{
Random gen = new Random();
int[] data = new int[x];
for (int index = 0; index<x; index ++)
data[index] = gen.nextInt(x);
}
public String toString()
{
String output = "";
for(int i = 0; i<data.length; i++)
{
output +=data[i];
}
return output;
}
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
int x;
int data;
System.out.println("please enter the number of integers you would like to create an array for");
x = scan.nextInt();
RandomArray table = new RandomArray(x);
table.toString();
From what I can tell this error means the toString is throwing null? But I do not know why that is, can anyone help me out?

You are redeclaring your data array which is hiding the one you are filling.
Random gen = new Random();
int[] data = new int[x]; // remove the int[] declaration
Also, it might be easier if you just did the following:
// your toString method
public String toString() {
return Arrays.toString(data);
}
In response to your question, you can do this.
int[] data; // you did this - leave it alone
// and later you should do this.
public RandomArray(int x) {
Random gen = new Random();
data = new int[x]; // designated as an array above
for (int index = 0; index<x; index ++)
data[index] = gen.nextInt(x);
}
}

why am I getting the cannot find symbol when passing an array into a method

can someone please tell me why I am getting this error when compiling?
import java.util.*;
import java.io.*;
public class StatsCalculator
{
public static void main (String[]args)
{
programHeader();
randomNo(random);
printArray(random);
}
public static void programHeader()//writes program header
{
System.out.println("****************");
System.out.println("Stats calculator");
System.out.println("****************");
}
public static int[] randomNo(int[] random)// fills an array with 10 random numbers
{
random = new int[10];
for (int i=0; i< random.length; i++){
int randomNumber= (int) (Math.random()*10)+1;
random[i] = randomNumber;
}
return random;
}
public static int[] printArray (int[] random)//prints array
{
System.out.println("Your ten random values are: ");
for (int i=0; i<random.length; i++){
System.out.print(Arrays.toString(random));
}
return random;
}
}
I am writing a simple program to fill and array with 10 random numbers 1-10 and then calculate the sum, mean, mode and median of all the random numbers but i can get the methods to work just to fill the array and to print the array.
any help is appreciated.

You should get return value of randomNo() then pass it to next method. This may help you:
import java.util.Arrays;
public class StatsCalculator {
public static void main(String[] args) {
programHeader();
int[] random = randomNo();
printArray(random);
}
public static void programHeader()//writes program header
{
System.out.println("****************");
System.out.println("Stats calculator");
System.out.println("****************");
}
public static int[] randomNo()// fills an array with 10 random numbers
{
int[] random = new int[10];
for (int i = 0; i < random.length; i++) {
int randomNumber = (int) (Math.random() * 10) + 1;
random[i] = randomNumber;
}
return random;
}
public static int[] printArray(int[] random)//prints array
{
System.out.println("Your ten random values are: ");
for (int i = 0; i < random.length; i++) {
System.out.print(Arrays.toString(random));
}
return random;
}
}

Printing a random string from my ArrayList to the console

Here's my code:
public static void main(String[] args) {
ArrayList<String> eMinor = new ArrayList<String>();
eMinor.add("E");
eMinor.add("F#");
eMinor.add("G");
eMinor.add("A");
eMinor.add("B");
eMinor.add("C");
eMinor.add("D");
}
What do I need to add in order to generate a random string from the list and print it in the console?

You can randomly select a value from the list with something like:
int index = new java.util.Random().nextInt(eMinor.size());
String value = eMinor.get(index);
and then print it to the console with:
System.out.println(value);

public static void main(String[] args) {
ArrayList<String> eMinor = new ArrayList<String>();
eMinor.add("E");
eMinor.add("F#");
eMinor.add("G");
eMinor.add("A");
eMinor.add("B");
eMinor.add("C");
eMinor.add("D");
Random rand = new Random()
int random = rand.nextInt(eMinor.size());
String note = eMinor.get(random);
System.out.println(note);
}

e minor is one of my favorite keys, so I'll answer. You need a random number generator:
Random ran = new Random();
int x = ran.nextInt(eMinor.size() - 1)
System.out.println(eMinor.get(x));
You could generate multiple notes with a loop:
Random ran = new Random();
for (int i = 0, i < 10; i++) {
int x = ran.nextInt(7)
System.out.println(eMinor.get(x));
}

You could do something like this:
int min = 3;
int range = 3;
Random random = new Random();
int length = min + random.nextInt(range);
String randomString = "";
for (int i = 0; i < length; ++i)
{
randomString += eMinor.get(random.nextInt(eMinor.size() - 1));
}
System.out.println(randomString);

You can use a simple model, but to complex application is necessary more attention with Random class;
enter code here
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
public class Main {
public static void main(String[] args) {
ArrayList<String> eMinor = new ArrayList<String>();
eMinor.add("E");
eMinor.add("F#");
eMinor.add("G");
eMinor.add("A");
eMinor.add("B");
eMinor.add("C");
eMinor.add("D");
for (int f = 0; f < 3; f++) {
System.out.printf("------------ list %s ------------\n",f);
for (String value : generateList(eMinor)) {
System.out.println(value);
}
}
}
private static List<String> generateList(ArrayList<String> eMinor) {
List<String> tempList = new ArrayList<>();
Random random = new Random();
while (tempList.size() != eMinor.size()) {
String value = eMinor.get(random.nextInt(eMinor.size()));
if (!tempList.contains(value)) {
tempList.add(value);
}
}
return tempList;
}
}

You may use the below complete example:
/*
* Created by Mohammed.Kharma on 2/9/2016.
*/
import java.util.Random;
import java.util.ArrayList;
public class Scrambler {
public static int[] Scramble(final int key, final int elementsCount) throws NegativeArraySizeException {
if (elementsCount < 0) {
NegativeArraySizeException ex = new NegativeArraySizeException("scrambler elementCount");
throw ex;
}
Random rand = new Random(key);
int[] order = new int[elementsCount];
for (int i = 0; i < elementsCount; i++) {
order[i] = i;
}
int count = elementsCount;
while (--count > 0) {
int nextRandom = rand.nextInt(count + 1); // 0 <= k <= count (!)
int temp = order[count];
order[count] = order[nextRandom];
order[nextRandom] = temp;
}
return order;
}
public static void main(String[] args) {
ArrayList<String> eMinor = new ArrayList<String>();
eMinor.add("E");
eMinor.add("F#");
eMinor.add("G");
eMinor.add("A");
eMinor.add("B");
eMinor.add("C");
eMinor.add("D");
for (int numOFRandoStrings = 0; numOFRandoStrings < 10; numOFRandoStrings++) {
int[] randomList = Scramble(new Long(System.currentTimeMillis()).intValue() * numOFRandoStrings, 7); //numOFRandoStrings or any seed,7 means give me 7 random numbers from zero to 6
StringBuffer randomString = new StringBuffer();
for (int ind = 0; ind < randomList.length; ind++) {
randomString.append(eMinor.get(randomList[ind] ));
}
System.out.println("New Random String: " + randomString);
}
}
}

Adding results from loop into Array?

I am currently just mocking about with Java. To get some learning in, and of course the easiest way to learn is by asking.
In this section I've created a loop to give me 50 random numbers. What I want to do, is to compare these numbers later on. That's why I want to move all the numbers into an array. I have no clue how. I've tried different stuff, but my syntax is wrong. Can somebody tell me how to do this?
Code:
package project.main;
import java.util.Random;
public class Main {
public static int numbers[];
public static final void main(String []args) {
getRandom();
recheckNumbers();
}
public static void getRandom() {
Random RandomNumber = new Random();
for(int i = 1; i <= 50; ++i){
int randomInt = RandomNumber.nextInt(100);
System.out.println("Generated : " + randomInt);
}
}
public static void recheckNumbers() {
if(numbers[0] < numbers[1]) {
System.out.println("numbers[0] is biggest");
} else {
System.out.println("numbers[1] is biggest");
}
}
}
I just rewrote it a bit. Im now running into another issue at line 14. which is the numbers[i] = randomInt part.
Heres the new code..
package project.main;
import java.util.Random;
public class Main {
public static int numbers[];
public static final void main(String []args) {
Random RandomNumber = new Random();
for(int i = 0; i <= 49; ++i){
int randomInt = RandomNumber.nextInt(100);
numbers[i] = randomInt;
}
}
}

for(int i = 0; i <= 49; ++i){
int randomInt = RandomNumber.nextInt(100);
numbers[i] = randomInt;
System.out.println("Generated : " + randomInt);
}
After that you can loop through to get number
for(int i = 0; i <= 49; ++i){
System.out.println("Generated : " + numbers[i]);
}
Solution to new question
import java.util.Random;
public class Main {
public static int[] numbers = new int[50];
public static void main(String[] args) {
Random RandomNumber = new Random();
for(int i = 0; i <= 49; ++i){
int randomInt = RandomNumber.nextInt(100);
numbers[i] = randomInt;
}
}
}

The solution lemon provided is correct.
Additionally I want to point you to a mistake you did in your recheckNumbers method. You check if numbers[0] is smaller than numbers[1] and print out that numbers[0] is the biggest in the if block. You should switch the output from the if and else block to return the correct answer.

You need to say the size of the array. Here is my solution to your problem:
public class Main {
public static int numbers[] = new int[50];
public static void main(String[] args) {
getRandom();
recheckNumbers();
}
public static void getRandom(){
Random randomNumber = new Random(); // variables should start with lower case
for(int i = 0; i < 50; i++){
int randomInt = randomNumber.nextInt(100); // generate a random integer in the (0-99) interval
System.out.println("Generated: " + randomInt); // print the generated number
numbers[i] = randomInt; // put it in the array
}
}
public static void recheckNumbers(){
if(numbers[0] > numbers[1]){
System.out.println("numbers[0] is bigger");
} else {
System.out.println("numbers[1] is bigger");
}
}
}
Hope it helps :)

Creating a random generated array in method and printing it

So I'm pretty sure I've correctly created a random integer generator that will put the integers into an array, although I am having trouble with my second method, that is supposed to print out the array.
My code:
import java.util.Random;
import java.util.Scanner;
public class Engine {
public int numDigits, numDigitsSet;
public int i;
public int[] secretNumber;
public Random randomNumberGenerator;
Scanner sc = new Scanner(System.in);
public void setNumDigits()
{
numDigitsSet = numDigits;
}
public int getNumDigits()
{
System.out.print("Enter the number of digits to use: ");
return numDigits = sc.nextInt();
}
public void generateNewSecret()
{
Random rand = new Random();{
for (int i=0; i<numDigitsSet; i++)
{
secretNumber[i]= rand.nextInt(10);
System.out.println("" + secretNumber[i]);
}
}
}
public int[] getSecretNumber()
{
for (int j=0; j<secretNumber.length; j++)
{
System.out.println("" + secretNumber[j]);
}
return secretNumber;
}
public void convertNumtoDigitArray()
{
String[] userGuessSplit = Player.userGuess.split(",");
int[] userGuessArray = new int[userGuessSplit.length];
for (int j=0; j<userGuessSplit.length; j++)
{
userGuessArray[j] = Integer.parseInt(userGuessSplit[j]);
}
}
}

For printing out the array, you can use the seriously convenient
Arrays.toString(array);
JavaDoc: http://docs.oracle.com/javase/7/docs/api/java/util/Arrays.html#toString(int[])