I am quite new to programming and I am just starting using java. My task was to write a program using quick sort, I managed to write it but it always gives me an index out of bounds. Could anyone take a look at my code and help me by identifying what I am doing wrong? Thanks
This is the code for the main class.
package quicksort;
public class Quicksort {
/**
* #param args the command line arguments
*/
public static void main(String[] args) {
// TODO code application logic here
int[] x = {5,3,10,1,9,8,7,4,2,6,0};
quicksort_class q = new quicksort_class(x);
q.sort();
for(int i = 0; i < 11-1; i++)
{
System.out.println(x[i]);
}
}
}
This is the code for quicksort_class.
public class quicksort_class {
int[] array1 = new int[11];
public quicksort_class(int[] w)
{
array1 = w;
}
public void partitionstep(int leftlimit, int rightlimit)
{
int LPointer = leftlimit;
int RPointer = rightlimit;
Random random = new Random();
int midpoint = random.nextInt(11);
int checknumber = array1[midpoint];
while(LPointer < RPointer)
{
while(array1[LPointer] <= checknumber)
{
LPointer = LPointer + 1;
}
while(array1[RPointer] >= checknumber)
{
RPointer = RPointer --;
}
swap(LPointer, RPointer);
partitionstep(leftlimit, midpoint - 1);
partitionstep(midpoint + 1, rightlimit);
}
}
public void swap(int x, int y)
{
int temp = array1[x];
array1[x] = array1[y];
array1[y] = temp;
}
public void sort()
{
partitionstep(0, array1.length - 1);
}
}
Your midpoint value should be calculated based on your leftLimit and rightLimit. It should not be a random value based off of the fixed value 11.
Related
I have written a simple genetic algorithm program in java. What it is does is maximize the decimal value represented by the bits in the chromosome. Somehow mutation is not working as expected, e.g. causing two genes to mutate when just one is to change. The print statements I have included there show which to mutate, but in addition to that some more chromosomes get mutated. I can't figure out what the problem is :-(
Here are my java classes.
Gene.java
public class Gene {
private int value;
public Gene() {
value = Math.random() < 0.5 ? 0 : 1;
}
public Gene(int value) {
if (value != 0 && value != 1) {
throw new IllegalArgumentException("value must be either 0 or 1");
}
else {
this.value = value;
}
}
public void mutate() {
value = 1 - value;
}
public int value() {
return value;
}
#Override
public String toString() {
return String.valueOf(value);
}
}
Chromosome.java
import java.util.ArrayList;
import java.util.List;
public class Chromosome implements Comparable {
private ArrayList<Gene> genes;
private final int chromosomeLength;
public Chromosome(int length) {
this.genes = new ArrayList<>();
this.chromosomeLength = length > 0 ? length : 16;
for (int i = 0; i < chromosomeLength; i++) {
this.genes.add(i, new Gene());
}
}
public List<Gene> getAllele(int fromIndex, int toIndex) {
return new ArrayList<>(genes.subList(fromIndex, toIndex));
}
public void setAllele(int fromIndex, List<Gene> allele) {
int lastIndex = fromIndex + allele.size();
if (lastIndex > chromosomeLength) {
throw new IndexOutOfBoundsException("the allele exceeds beyond the size of the chromosome");
}
for (int i = fromIndex, j = 0; i < lastIndex; i++, j++) {
genes.set(i, allele.get(j));
}
}
public int getChromosomeLength() {
return chromosomeLength;
}
public void setGeneAt(int index, Gene gene) {
genes.set(index, gene);
}
public Gene getGeneAt(int index) {
return genes.get(index);
}
public int value() {
return Integer.parseInt(this.toString(), 2);
}
#Override
public String toString() {
StringBuilder chromosome = new StringBuilder("");
genes.stream().forEach((Gene g) -> chromosome.append(g));
return chromosome.toString();
}
#Override
public int compareTo(Object anotherChromosome) {
Chromosome c = (Chromosome) anotherChromosome;
return this.value() - c.value();
}
}
GenePool.java
import java.util.ArrayList;
import java.util.Arrays;
public class GenePool {
private final ArrayList<Chromosome> genePool;
private final int genePoolSize;
private final int chromosomeLength;
private final double crossOverRate;
private final double mutationRate;
private int[] crossPoints;
public GenePool(int numOfChromosome, int chromosomeLength, double crossOverRate, double mutationRate) {
this.genePoolSize = numOfChromosome;
this.chromosomeLength = chromosomeLength > 0 ? chromosomeLength : 16;
this.crossOverRate = crossOverRate;
this.mutationRate = mutationRate;
crossPoints = new int[1];
crossPoints[0] = this.chromosomeLength / 2;
genePool = new ArrayList<>();
for (int i = 0; i < numOfChromosome; i++) {
genePool.add(new Chromosome(chromosomeLength));
}
}
public int getGenePoolSize() {
return genePoolSize;
}
public Chromosome getChromosomeAt(int index) {
return genePool.get(index);
}
public void setChromosomeAt(int index, Chromosome c) {
genePool.set(index, c);
}
public int getChromosomeLength() {
return chromosomeLength;
}
public Chromosome[] crossOver(Chromosome c1, Chromosome c2) {
Chromosome[] offsprings = new Chromosome[2];
offsprings[0] = new Chromosome(c1.getChromosomeLength());
offsprings[1] = new Chromosome(c1.getChromosomeLength());
Chromosome[] parentChromosomes = {c1, c2};
int selector = 0;
for (int i = 0, start = 0; i <= crossPoints.length; i++) {
int crossPoint = i == crossPoints.length ? c1.getChromosomeLength() : crossPoints[i];
offsprings[0].setAllele(start, parentChromosomes[selector].getAllele(start, crossPoint));
offsprings[1].setAllele(start, parentChromosomes[1 - selector].getAllele(start, crossPoint));
selector = 1 - selector;
start = crossPoint;
}
return offsprings;
}
public void mutateGenePool() {
int totalGeneCount = genePoolSize * chromosomeLength;
System.out.println("Mutating genes:");
for (int i = 0; i < totalGeneCount; i++) {
double prob = Math.random();
if (prob < mutationRate) {
System.out.printf("Chromosome#: %d\tGene#: %d\n", i / chromosomeLength, i % chromosomeLength);
genePool.get(i / chromosomeLength).getGeneAt(i % chromosomeLength).mutate();
}
}
System.out.println("");
}
public int getLeastFitIndex() {
int index = 0;
int min = genePool.get(index).value();
int currentValue;
for (int i = 1; i < genePoolSize; i++) {
currentValue = genePool.get(i).value();
if (currentValue < min) {
index = i;
min = currentValue;
}
}
return index;
}
public void saveFittest(ArrayList<Chromosome> offsprings) {
// sort in ascending order
offsprings.sort(null);
offsprings.stream().forEach((offspring) -> {
int leastFitIndex = getLeastFitIndex();
if (offspring.value() > genePool.get(leastFitIndex).value()) {
genePool.set(leastFitIndex, offspring);
}
});
}
public void evolve(int noOfGeneration) {
for (int generation = 1; generation <= noOfGeneration; generation++) {
System.out.println("Generation :" + generation);
ArrayList<Integer> selection = new ArrayList<>();
for (int i = 0; i < genePoolSize; i++) {
if (Math.random() <= crossOverRate) {
selection.add(i);
}
}
if (selection.size() % 2 == 1) {
selection.remove(selection.size() - 1);
}
ArrayList<Chromosome> offsprings = new ArrayList<>();
for (int i = 0; i < selection.size(); i += 2) {
int index1 = selection.get(i);
int index2 = selection.get(i + 1);
offsprings.addAll(Arrays.asList(crossOver(genePool.get(index1), genePool.get(index2))));
}
System.out.println("Before saving the offsprings");
displayChromosomes(genePool, "GenePool");
displayChromosomes(offsprings, "Offsprings");
saveFittest(offsprings);
System.out.println("Before mutation:");
displayChromosomes(genePool, "GenePool");
mutateGenePool();
System.out.println("After mutation:");
displayChromosomes(genePool, "GenePool");
System.out.println("\n\n");
}
}
public void displayChromosomes(ArrayList<Chromosome> geneList, String name) {
System.out.println(name);
if (geneList.isEmpty()) {
System.out.println("Empty list");
}
geneList.stream().forEach((c) -> {
System.out.println(c + " -> " + c.value());
});
System.out.println("");
}
}
GADemo.java
public class GADemo {
public static void main(String[] args) {
GenePool gp = new GenePool(6, 8, 0.25, 0.01);
gp.evolve(10);
}
}
After evolving for a number of generations, the chromosomes all tend to become exactly the same, or very similar. And the problem is that that value is not the maximum for that many bits, and sometimes even a small value. For example, for 8 bits the values should (tend to) approach 255, but this doesn't do so in my code. Someone please provide a hint where/how to look for and solve the problem.
Focus on these lines and imagine the references. These are from setAllele()
for (int i = fromIndex, j = 0; i < lastIndex; i++, j++) {
genes.set(i, allele.get(j));
}
You are basically copying the reference from one onto the other. They are the same Gene so whatever mutation you do on those genes, will also affect even other Chromosomes.
You must produce a deep copy here.
Initially each chromosome has an own list of genes. But when you do the crossover operation you set gene objects from one chromosome into the gene list of other chromosome.
When you evolve the system, the number of shared genes will rise and therefore ultimately all chromosomes will share the same genes. No matter how you mutate a gene the chromosomes are not affected.
EDIT:
As Incognito also answered the setAllele method seems to be the culprit where gene sharing starts. You may want to introduce a method in the gene class where you can set its value given another gene.
So I'm creating a hash table with LinkedLists using the multiplication method. As an instance variable I define the LinkedList "T" that I'll be using, and in the constructor of the class I specify the size of T. However, every time I run my Driver testing class, I get NullPointerExceptions on everything I try to reference anything in T[]. Am I overlooking something? I've spent over an hour trying to figure it out.
ChainedHashTable class:
public class ChainedHashTable
{
private LinkedList<Integer>[] T;
private int m;
private double A;
public ChainedHashTable(int n)
{
for (m = 1; m < n; m *= 2);
T = new LinkedList[m];
Random random = new Random();
int s = random.nextInt(Integer.MAX_VALUE);
A = (s * 1.00) / Integer.MAX_VALUE;
}
public void insert(Integer key)
{
T[hash(key)].add(Integer.valueOf(key));
}
public void delete(int key)
{
T[hash(key)].remove(Integer.valueOf(key));
}
public Integer search(int key)
{
int n = T[hash(key)].indexOf(key);
if (n == -1)
return -1;
else
return T[hash(key)].get(n);
}
private int hash(int key)
{
System.out.println((int)(m * ((key * A) % 1)));
return (int)(m * ((key * A) % 1));
}
public void printTable()
{
for (int i = 0; i < T.length; i++)
{
System.out.println("index: " + i + " " + T[i]);
}
}
}
Driver class:
public class Driver
{
public static void main(String[] args)
{
ChainedHashTable test1 = new ChainedHashTable(20);
test1.printTable();
test1.insert(4);
test1.insert(54);
test1.insert(6);
test1.insert(3);
test1.insert(26);
test1.insert(54);
test1.insert(11);
test1.insert(10);
test1.insert(76);
test1.insert(42);
test1.insert(41);
test1.insert(32);
test1.insert(87);
test1.insert(76);
test1.insert(72);
test1.insert(57);
test1.insert(29);
test1.insert(16);
test1.insert(92);
test1.insert(64);
test1.printTable();
}
}
You are creating an array of references to type LinkedList and setting them to their initial state, which is null.
T = new LinkedList[m];
T now is an array of the computed size m. You need to initialize the objects inside of the array.
T = new LinkedList[m];
for (int i = 0; i < m; i++) {
T[i] = new LinkedList<>();
}
my friend has programmed a Breakout game in java. I know C++, which tranfers relatively well to java.
I had a problem when trying to insert a MultiBall brick.
Here are the relevent bits of my function:
private Balle[] balle;
public BriqueMultiBalle(Balle[] bal) {
super();
balle = bal;
SCORE = 100;
}
public void touched() {
visible = false;
balle[Balle.getNInstance()].makeVisible();
}
I get no error but I found out when debugging that balle corresponds to a null pointer. I tried using these different declarations, however, none of them worked:
1.
public BriqueMultiBalle(Balle[] bal) {
super();
for(int i = 0; i < 6; i++)
{
balle[i] = bal[i];
}
SCORE = 100;
}
2.
public BriqueMultiBalle(Balle[] bal) {
super();
balle = new Balle[](bal);
SCORE = 100;
}
However, these methods do not work.
Thanks,
Ghi102
You are getting a null pointer on balle because you never initialize the array, you leave it as
private Balle[] balle;
Try initializing you code
balle = new Balle[bal.length];
for(int i = 0; i < bal.length; i++){
balle[i] = bal[i];
}
Here's an example I wrote using an int array. Same concept, just apply it to your object.
public static void main(String[] args) throws Exception {
int[] arrayInts;
int[] originalInts = { 1, 2, 3, 4, 5 };
arrayInts = new int[originalInts.length];
for(int i = 0; i < originalInts.length; i++){
arrayInts[i] = originalInts[i];
}
originalInts[0] = 10;
for (int i : arrayInts) {
System.out.println(i);
}
}
I am trying to create a random sized array of 1's and 0's. I can get the program to run and compile if I remove the random aspect of the of it and enter the size of the array manually. For some reason when I bring in the random utility I can not get the program to compile.
mport java.util.Random;
public class Project1a {
int[][] sample={{0,0,1,1,1},
{1,1,0,1,1},
{1,1,1,0,1},
{0,1,0,1,1}};
int box[][];
Random randomNumbers = new Random();
int m = randomNumbers.nextInt(100);
int n = randomNumbers.nextInt(100);
int results[][] = new int [m][n];
int goodData = 1;
public static void main(String[] args){
analyzeTable();
printTable(results);
}
public void analyzeTable() {
int row=0;
while (row < sample.length) {
analyzeRow(row);
row++;
}
}
public void analyzeRow(int row) {
int xCol = 0;
int rCount = 0;
while (xCol < sample[row].length) {
rCount = analyzeCell(row,xCol);
results[row][xCol] = rCount;
xCol++;
}
}
int analyzeCell(int row, int col) {
int xCol = col;
int runCount = 0;
int rowLen = sample[row].length;
int hereData = sample[row][xCol];
while (hereData == goodData && xCol < rowLen) {
runCount++;
xCol++;
if (xCol < rowLen) { hereData = sample[row][xCol];}
}
return runCount;
}
public void printTable(int[][] aTable ) {
for (int[] row : aTable) {
printRow(row);
System.out.println();
}
}
public void printRow(int[] aRow) {
for (int cell : aRow) {
System.out.printf("%d ", cell);
}
}
}
Your class name conflicts with java.util.Random. Renaming your class is the easiest fix here.
the problem is you are declaring your instance variable in a block which makes it in-accessible in methods
check this : remove curly braces { } from here and the way you are accessing your results and goodData you need to declare them static
{ // remove this
Random randomNumbers = new Random();
int m = randomNumbers.nextInt(100);
int n = randomNumbers.nextInt(100);
static int results = new int [m][n];
static int goodData = 1;
} // remove this
I have been developing an implementation of the neighbourhood algorithm in Java for a physics project I am working on. I'm brand new to Java so I apologize for any idiocy that results.
I have been getting the error
''
incompatible types
found : void
required: java.util.List<VoronoiPoint>
'' on line 22 from the Java compiler in attempting to compile the program shown below. I cannot figure out why the variable ''thelist'' somehow turns into a void when I declared it to be of type List<VoronoiPoint>. If anybody can explain to me what is going on it would be much appreciated!
import java.lang.Double;
import java.util.*;
public class VoronoiTiling
{
public static void main(String args[])
{
Integer n = 10; //Number of dimensions of model parameter space
Integer ns = 20; //Number of points per iteration
Integer nr = 4; //Number of cells to populate
Integer iterations = 5; //Number of iterations
List<VoronoiPoint> thelist = VoronoiList.startlist(ns,n);
//System.out.println(thelist);
//System.out.println(thelist.get(1).misfit);
for (Integer i=0 ; i<thelist.size() ; i++)
{
thelist.get(i).setmisfit();
}
List<VoronoiPoint> orderedlist = Collections.sort(thelist);
Double distance = EuclidianDistance((thelist.get(1)).location,(thelist.get(2)).location);
System.out.println(distance);
}
public static Double EuclidianDistance(Double[] point1, Double[] point2)
{
Double distance=0.0;
for (int i = 0; i < point1.length; i++)
{
distance = distance + Math.pow((point1[i]-point2[i]),2);
}
return Math.sqrt(distance);
}
}
The other classes I used are here:
The VoronoiList class:
import java.util.*;
public class VoronoiList
{
public static List<VoronoiPoint> startlist(Integer ns, Integer n)
{
List<VoronoiPoint> thestartlist = new ArrayList<VoronoiPoint>();
for (int i = 0; i < ns; i++)
{
thestartlist.add(new VoronoiPoint(0.,n));
}
return thestartlist;
}
}
The VoronoiPoint class:
import java.util.Random;
public class VoronoiPoint implements Comparable<VoronoiPoint>
{
Double[] location;
private Random generator = new Random();
Double misfit = -1.;
//***************************************************************
public VoronoiPoint(Double misfit, Integer n)
{
location = new Double[n];
ParameterBoundaries boundaries = new ParameterBoundaries(n);
for(int i = 0; i < n; i++)
{
location[i] = boundaries.getboundaries(2*i)+2*generator.nextDouble();
}
}
//***************************************************************
//public Double[] getlocation()
//{
//return location;
//}
public void setlocationi(Integer i, Double j)
{
location[i] = j;
}
//***************************************************************
public void setmisfit()
{
Integer n = location.length;
Double tempmisfit = 0.0;
for(Integer i = 0; i < n; i++)
{
tempmisfit = tempmisfit + Math.pow((location[i]),2);
}
misfit = Math.sqrt(tempmisfit); // Temporarily just distance to centre
}
//public Double getmisfit()
//{
//return misfit;
//}
public int compareTo(VoronoiPoint b)
{
if (this.misfit<b.misfit) return -1;
else if (this.misfit==b.misfit) return 0;
return 1;
}
}
And the parameter boundaries class:
public class ParameterBoundaries
{
private Double[] boundaries; /*Set to 2n where n is dimensions of parameter space,
* it just makes it easier*/
public ParameterBoundaries(Integer n)
{
boundaries = new Double[2*n];
for(Integer i = 0; i<n; i++)
{
boundaries[2*i] = -1.0;
boundaries[2*i+1] = 1.0;
}
}
public Double getboundaries(Integer i)
{
return boundaries[i];
}
}
Collections.sort(..) sorts the original list. It doesn't return a new list. (Its return type is void)
Your code is wrong. Collections.sort() is an in-place sort function; it modifies the given list argument and returns nothing (void).