My statement is returning that the value of x is 0 but it is clearly 5.
The return Statement is
"5" and "yeah"
import java.util.ArrayList;
public class DeletionEasyTester {
public static void main(String Args[]){
int x = 1;
ArrayList<Integer> list1 = new ArrayList<>();
list1.add(3);
list1.add(5);
list1.add(8);
list1.add(0);
list1.add(2);
list1.add(5);
list1.add(4);
x = list1.get(1);
System.out.println(x);
if(x == 0);
{
System.out.print("yeah");
}
}
}
The problem is here: if(x == 0);. It should be if(x == 0), without ;.
In your version of the code, there is an empty code block after the if statement, and System.out.print("yeah"); is in a block unrelated to the if-statement.
Related
I am new to JAVA. I don't understand why JAVA give me two souts.
(Input row & column (throw 1 space): Input row & column (throw 1 space): )
In the first pass, it does not wait for my input and think str = "". And in the second pass its waiting for my input.
Ssory, I forgot to tell that beforŠµ this block of code - my Scanner was opened. I asked program:
while (true) {
System.out.print("Enter game size (3 - 20): ");
if (SCAN.hasNextInt()) {
return SCAN.nextInt();
}
System.out.println(SCAN.next() + " - not a number!");
I think I should clear scanners buffer ( /n ). But I dont know how.
private static void humanTurn() {
System.out.println("HUMAN TURN");
String str;
String regex = "\\d{1,2}\\s\\d{1,2}";
Pattern myPattern = Pattern.compile(regex); // Pattern for checking
boolean checkPattern;
int x, y;
do {
do {
System.out.print("Input row & column (throw 1 space): ");
str = SCAN.nextLine();
Matcher myMatcher = myPattern.matcher(str);
checkPattern = myMatcher.matches();
} while (!checkPattern);
String[] strArr = str.split(" ");
x = Integer.parseInt(strArr[0]) - 1;
y = Integer.parseInt(strArr[1]) - 1;
} while (!isValidCell(x, y));
I have tried to guess your code. This is what I come up with. Still works fine. Let me know if anything else.
import java.util.Scanner;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class Main {
private static Scanner sc = new Scanner(System.in);
private static int size = 0;
public static void main(String[] args) {
size = getBoardSize();
humanTurn();
}
private static int getBoardSize() {
while (true) {
System.out.print("Enter game size (3 - 20): ");
if (sc.hasNextInt()) {
return sc.nextInt();
}
System.out.println(sc.next() + " - not a number!");
}
}
private static void humanTurn() {
System.out.println("HUMAN TURN");
String str;
String regex = "\\d{1,2}\\s\\d{1,2}";
Pattern myPattern = Pattern.compile(regex); // Pattern for checking
boolean checkPattern;
int x, y;
do {
do {
System.out.print("Input row & column (throw 1 space): ");
str = sc.nextLine();
Matcher myMatcher = myPattern.matcher(str);
checkPattern = myMatcher.matches();
} while (!checkPattern);
String[] strArr = str.split(" ");
x = Integer.parseInt(strArr[0]) - 1;
y = Integer.parseInt(strArr[1]) - 1;
} while (!isValidCell(x, y));
}
private static boolean isValidCell(int x, int y) {
return x < size && y < size && x >= 0 && y >= 0;
}
}
I cannot get the loop to work in the buildDimArray method to store the number combinations "11+11", "11+12", "11+21", "11+22", "12+11", "12+12", "12+21", "12+22", "21+11", "21+12", "21+21", "21+22", "22+11", "22+12", "22+21", and "22+22" into the 2d arraylist with each expression going into one column of the index dimBase-1 row. The loop may work for other people, but for some reason mine isn't functioning correctly. The JVM sees the if dimBase==1 condition, but refuses to check the other conditions. The "WTF" not being printed as a result from the buildDimArray method. If dimBase=1, it prints successfully, but doesn't for the other integers. The dimBase==3 condition needs a loop eventually. The "WTF" is for illustrative purposes. I could get away with a 1d arraylist, but in the future I will likely need the 2d arraylist once the program is completed.
package jordanNumberApp;
import java.util.Scanner;
import java.util.ArrayList;
/*
* Dev Wills
* Purpose: This code contains some methods that aren't developed. This program is supposed to
* store all possible number combinations from numbers 1-dimBase for the math expression
* "##+##" into a 2d arraylist at index row dimBase-1 and the columns storing the
* individual combinations. After storing the values in the arraylist, the print method
* pours the contents in order from the arraylist as string values.
*/
public class JordanNumberSystem {
// a-d are digits, assembled as a math expression, stored in outcomeOutput, outcomeAnswer
public static int dimBase, outcomeAnswer, a, b, c, d;
public static String inputOutcome, outcomeOutput;
public static final int NUM_OF_DIMENSIONS = 9; //Eventually # combinations go up to 9
public static ArrayList<ArrayList<String>> dimBaseArray;
public static Scanner keyboard;
/*
* Constructor for JordanNumber System
* accepts no parameters
*/
public JordanNumberSystem() // Defunct constructor
{
// Declare and Initialize public variables
this.dimBase = dimBase;
this.outcomeOutput = outcomeOutput;
this.outcomeAnswer = outcomeAnswer;
}
// Set all values of variable values
public static void setAllValues()
{
// Initialize
dimBase = 1;
outcomeAnswer = 22; // variables not used for now
outcomeOutput = "1"; // variables not used for now
//a = 1;
//b = 1;
//c = 1;
//d = 1;
dimBaseArray = new ArrayList<ArrayList<String>>();
keyboard = new Scanner(System.in);
}
public static void buildDimArray(int dim)
{
dimBase = dim;
try
{
//create first row
dimBaseArray.add(dimBase-1, new ArrayList<String>());
if( dimBase == 1)
{
a = b = c = d = dimBase ;
dimBaseArray.get(0).add(a+""+b+"+"+c+""+d);
System.out.println("WTF"); // SHOWS
}
else if (dimBase == 2)
{ // dim = 2
a = b = c = d = 1 ;
System.out.println("WTF"); // doesn't show
// dimBaseArray.get(dimBase-1).add(a+""+b+"+"+c+""+d);
for( int i = 1 ; i <= dim ; i++)
a=i;
for( int j = 1 ; j <= dim ; j++)
b=j;
for( int k = 1 ; k <= dim ; k++)
c=k;
for( int l = 1 ; l <= dim ; l++)
{
d=l;
dimBaseArray.get(dim-1).add(a+""+b+"+"+c+""+d);
}
}
else if (dimBase == 3)
{
a = b = c = d = dimBase;
dimBaseArray.get(2).add(a+""+b+"+"+c+""+d);
System.out.println("WTF");
}
}catch (IndexOutOfBoundsException e)
{
System.out.println(e.getMessage());
}
}
public static void printArray(int num) // Prints the contents of the array
{ // Fixing the printing method
try
{
int i = num-1;
for( String string : dimBaseArray.get(i))
{
System.out.println(string);
System.out.println("");
}
} catch (IndexOutOfBoundsException e)
{
System.out.println(e.getMessage());
}
}
public static void main(String[] args) throws java.lang.IndexOutOfBoundsException
{
setAllValues(); // sets the initial a,b,c,d values and dimBase, initializes 2d arraylist
// Get the Dimension Base number
System.out.println("Enter Dimension Base Number. Input an integer: ");
int dimBaseInput = keyboard.nextInt(); // Receives integer
dimBase = dimBaseInput;
if( dimBase != 1 && dimBase != 2 && dimBase != 3)
{// Error checking
System.out.println("invalid Dimension Base Number should be 1 or 2 ");
System.exit(1);
}
// Build the arraylist, print, clear, exit
buildDimArray(dimBase);
printArray(dimBase);
dimBaseArray.clear();
System.exit(1);
}
}// End of class
package LinkList2;
//import java.util.*;
public class Duplicates {
public static void removeDuplicates(LinkedListNode head)
{
LinkedListNode current = head;
while(current!= null && current.next!= null)
{
LinkedListNode curr = current;
while(curr!=null)
{
if(curr.next.data==current.data) //Getting error at this line
curr.next = curr.next.next;
else
curr = curr.next;
}
current = current.next;
}
}
public static void main(String args[])
{
LinkedListNode first = new LinkedListNode(0,null,null);
LinkedListNode head = first;
LinkedListNode second = first;
for(int i=1; i< 8; i++)
{
second = new LinkedListNode(i%2, null, null);
first.setNext(second);
second.setPrevious(first);
}
System.out.println(head.printForward());
removeDuplicates(head);// Getting error at this line
}
}
Getting null pointer exception in the above code. When I try to run the above code, it gives null pointer exception.
Please help me with my mistake.
Below is the implementation of LinkList where all the methods are defined
class LinkedListNode {
public LinkedListNode next;
public LinkedListNode prev;
public LinkedListNode last;
public int data;
public LinkedListNode(int d, LinkedListNode n, LinkedListNode p) {
data = d;
setNext(n);
setPrevious(p);
}
public void setNext(LinkedListNode n) {
next = n;
if (this == last) {
last = n;
}
if (n != null && n.prev != this) {
n.setPrevious(this);
}
}
public void setPrevious(LinkedListNode p) {
prev = p;
if (p != null && p.next != this) {
p.setNext(this);
}
}
public String printForward() {
if (next != null) {
return data + "->" + next.printForward();
} else {
return ((Integer) data).toString();
}
}
public LinkedListNode clone() {
LinkedListNode next2 = null;
if (next != null) {
next2 = next.clone();
}
LinkedListNode head2 = new LinkedListNode(data, next2, null);
return head2;
}
}
You are getting an exception just because of the following condition:
while(curr != null)
Replace it with while(curr != null && curr.next != null) this way you can check if you have the next element.
Hope this helps.
The problem is that here:
while(curr != null)
{
if(curr.next.data==current.data) //Getting error at this line
curr.next = curr.next.next;
else
curr = curr.next;
}
You are accessing the curr.next.data where you are not checking if that node is null or not. This through your NullPointerException.
To fix your problem is to check on the while loop, if the .next is also not null.
while(curr != null && curr.next != null)
{
if(curr.next.data==current.data) //Getting error at this line
curr.next = curr.next.next;
else
curr = curr.next;
}
In other words, you are not checking if your next node is actually the end of the linked list (i.e null). If you need in your program logic to handle this separately, then you should remove the check from the while loop, and implement this check differently.
I have the following problem. I'm trying to show all the elements of a display arrayList but I can only see the last item repeated as many times as there are number of elements in the ArrayList.
import java.util.ArrayList;
import java.util.Iterator;
public class PurebaArrayList {
public static void main(String[] args) {
ArrayList<PuntoDouble> puntos = new ArrayList<>();
PuntoDouble p = new PuntoDouble();
for(int cont = 0; cont< 100; cont++){
p.setX(cont);
p.setY(cont);
puntos.add(p);
}
System.out.println(puntos.toString());
}
}
public class PuntoDouble{
private double x;
private double y;
public PuntoDouble(double x, double y) {
this.x = x;
this.y = y;
}
public PuntoDouble(){
}
public double getX() {
return x;
}
public void setX(double x) {
this.x = x;
}
public double getY() {
return y;
}
public void setY(double y) {
this.y = y;
}
#Override
public String toString() {
return "PuntoDouble{" + "x=" + x + ", y=" + y + '}';
}
}
Thanks
You need to create a new PuntoDouble for every entry you add to the list. At the moment you add just a single instance of a PuntoDouble which you modify.
Therefore change the code to:
for(int cont = 0; cont< 100; cont++){
PuntoDouble p = new PuntoDouble();
p.setX(cont);
p.setY(cont);
puntos.add(p);
}
You are, literally, adding the same PuntoDouble as each of the 100 elements of the array. If you want them to be distinct from each other, you need to make a new one for each.
For debugging,slightly change 100 to 3 and add for each iteration to print out the elements in puntos.
// adds to ArrayList
for(int cont = 0; cont< 10; cont++){
p.setX(cont);
p.setY(cont);
System.out.println("[add]" + p);
puntos.add(p);
}
// iterates ArrayList puntos' elements
for(PuntoDouble pd : puntos){
System.out.println("[contain]" + pd);
}
debug output lines:
[add]PuntoDouble{x=0.0, y=0.0}
[add]PuntoDouble{x=1.0, y=1.0}
[add]PuntoDouble{x=2.0, y=2.0}
[add]PuntoDouble{x=3.0, y= 3.0}
[contain]PuntoDouble{x=9.0, y=9.0}
[contain]PuntoDouble{x=9.0, y=9.0}
[contain]PuntoDouble{x=9.0, y=9.0}
What you did is created an PuntoDouble object p and initilized it by invoking default constructor. In the for loop, the values of p modifies, but the reference of p never changed, therefore you kept adding the same object into ArrayList 100 times, all of those added objects refer to the same address in memory(new an object once before the for loop) which the value x is 99.0 and y is 99.0 (the last added values)
What you should do is creating a new object each iterate.
for(int cont = 0; cont< 100; cont++){
puntos.add(new PuntoDouble(cont, cont));
}
I have interface that returns a iterable object.
I need to iterate on the first 1000 items of it.
What is the best way to combine iterating using Iterator and stop after a certain count is reached.
Thanks
I'd use a loop that iterates and have a counter variable incremented; then break out of the loop when the counter reaches 1000.
What is your language?
C#:
using System.Linq;
//...
foreach (var item in iface.GetIterable().Take(1000))
{
//...
}
Python:
import itertools
#...
for item in itertools.islice(iface.get_iterable(), 1000):
#...
Make a standard loop that iterates over your collection, but check to see if the index has progress past the target index.
You may want to extract a seperate counter from the main loop index for your specific application.
int stopIndex = 1000;
for (int index = 0; index <= theInterface.Count; index++)
{
// check to see if we're at/past the stopIndex
if (index >= stopIndex)
break;
// we're still within the conditions, so do something with your interface
myObjectType localObject = (MyObjectType)theInterface.IndexOf(index);
}
Here's a test-driven (Java) wrapper around any existing iterator that should do the trick.
package com.playground;
import java.util.Arrays;
import java.util.Iterator;
import java.util.List;
import junit.framework.TestCase;
public class LimitedIterableTest extends TestCase {
private static class LimitedIterator<T> implements Iterator<T> {
private final Iterator<T> original;
private final int limit;
private int index = 0;
public LimitedIterator(Iterator<T> iterator, int limit) {
this.original = iterator;
this.limit = limit;
}
public boolean hasNext() {
return index < limit && original.hasNext();
}
public T next() {
index++;
return original.next();
}
public void remove() {
original.remove();
}
}
private static class LimitedIterable<T> implements Iterable<T> {
private final int limit;
private final Iterable<T> original;
public LimitedIterable(Iterable<T> iterable, int limit) {
this.original = iterable;
this.limit = limit;
}
public Iterator<T> iterator() {
return new LimitedIterator<T>(original.iterator(), limit);
}
}
final Integer[] array = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
final List<Integer> list = Arrays.asList(array);
public void testCount() throws Exception {
assertEquals(10, count(list));
}
public void testLimitedIterable() throws Exception {
Iterable<Integer> limited = new LimitedIterable<Integer>(list, 5);
assertEquals(5, count(limited));
limited = new LimitedIterable<Integer>(list, 50);
assertEquals(10, count(limited));
}
private static <T> int count(Iterable<T> iterable) {
Iterator<T> iterator = iterable.iterator();
return count(iterator);
}
private static <T> int count(Iterator<T> iterator) {
int count = 0;
while (iterator.hasNext()) {
iterator.next();
count++;
}
return count;
}
}