this may seem daft i have a class called ship locations which i wish to store all my ships locations, ive extended it from my client class and simply called the set method as follows
sub.local being a multidimensional array from the ship class
sub.local = new int[2][2];
sub.local[0][0] =row;
sub.local[0][1]=col;
sub.local[1][0]=row;
sub.local[1][1] =col+1;
toServer.writeInt(row);
toServer.writeInt(col);
toServer.writeChar('s');
sub.placed=true;
setp1sub(sub.local);
When i print it back through another class it comes back with the location in the memory rather than the numbers i need. What is the reason for this
public class ShipLocations {
static int [][] p1sub;
public ShipLocations()
{
p1sub = new int[2][2];
}
public int[][] getp1sub()
{
return p1sub;
}
public void setp1sub(int[][] local) {
for (int i = 0;i <local.length;i++)
{
for(int j = 0;j<local.length;j++)
{
p1sub [i][j]= local[i][j];
}
}
}
}
would it be that im passing it as sub.local ?
output is [[I#a401c2
Instead of writing
System.out.println(yourArray);
use
// for multidemensional arrays:
System.out.println(Arrays.deepToString(yourArray));
// or for one dimemsional arrays:
System.out.println(Arrays.toString(yourArray));
Here is a link to the relevant JavaDoc.
For an explanation of your output, you can look at this answer.
Related
Good morning,
I have one little problem.
I created one class named Map(). In this class there in one method that generate an Array. Then i created other two classes (Top and Bottom) that extend Map. Then I created 2 objects. One of Top and one of Bottom. I want to get the same array for the Top's object and for the Bottom's object. Here is the code Source:
public class Map{
public Map(){}
public int [] yTopValues()
{
int [] arrayTopY = new int[100];
for(int i=0;i<100;i++)
arrayTopY[i]=randomInt(-50,50);//it puts in i-th position an int between 50 and -50
return arrayTopY;
}
public int [] yBottomValues()
{
int [] arrayBottomY = yTopValues;
for(int i=0;i<100;i++)
arrayBottomY[i]=arrayBottomY[i]-250;
return arrayBottomY;
}
public int [] xValues()
{
int [] arrayX = new int[100];
for(int i=0;i<100;i++)
arrayX[i]=randomInt(0,50);//it puts in i-th position an int between 0 and 50
return arrayX;
}
//other stuff
}
public class TopMap extends Map{
public TopMap(){
this.area=new Area(new Polygon(
this.xValues,
this.yTopValues,
200)
);
}
public class BottomMap extends Map{
public BottomMap(){
this.area=new Area(new Polygon(
this.xValues,
this.yBottomValues,
200)
);
}
In the View class I created two objects one of TopMap and one of BottomMap then I drew the areas with g2.draw(topMap.area) and g2.draw(bottomMap.area)
I need the 2 polygons to be similar, but both of them are different because the method is executed twice. What should I do?
Thank you very much!!
The class Map does not hold the array. It is local only to the xValues() method. If you want the other classes to get that exact array do this:
/*
* Since this is a variable in the CLASS field, this object will
* be accessible to the child class.
*/
private int[] arrayX = new int[100];
public Map(){
createArrayX(); // This makes sure that the array is created, or else
// every value inside of it will be 0.
}
public void createArrayX(){ // Exact same thing as xValues(), but without the return type
for(int i=0;i<100;i++){
arrayX[i]=randomInt(0,50);
}
}
public int[] getArrayX(){ // The method that gets the array.
return arrayX;
}
So lets say I have a class BaseballCard that creates a baseball card.
Now I need to make another class which would be my collection class.
For example I would call it BaseballCardCollection
and then I want to create methods like
size (which returns the numbers of cards in the collection)
addCard(adds a baseball object to the collection object)
removeCard (removes a baseball card)
and so on
What would be the best way to do this. I tried doing this
public CardCollectionList() {
BaseballCard[] baseballCardList = new BaseballCard[101];
}
So each object is insinuated with an array of type BaseballCard of size 100.
And then for example the size method I tried something like this
public int size(){
int size = 0;
for(int i = 1; i<this.baseballCardList.length; i++)
if (baseballCardList!= null)
size+=1;
}
But it doesn't work because "baseballCardList cannot be resolved to a variable"
You could try using ArrayLists - http://docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html:
ArrayList<baseballCard> baseballCardList = new ArrayList<baseballCard>(0);
public boolean addCard(baseballCard card){
return baseballCardList.add(card);
}
public boolean removeCard(int card){
return baseballCardList.remove(card);
}
public baseballCard getCard(int card){
return baseballCardList.get(card);
}
public int sizeBaseballCardList(){
return baseballCardList.size();
}
public ArrayList<baseballCard> getBaseballCardList(){
return baseballCardList;
}
Move the variable BaseballCard[] baseballCardList outside the constructor, make it a field in your class. Do similar with size.
This is how the class should look like:
public class CardCollectionList {
//fields
private BaseballCard[] baseballCardList;
private int size;
//constructor
public CardCollectionList() {
baseballCardList = new BaseballCard[101];
}
//method
public int getSize() {
return this.size;
}
}
You could try creating your own class implementing the Collection interface and define your own methods + implement Collection methods:
public class myContainer implements Collection <BaseballCard> {
}
You need to move the variable declaration from the constructor to the class, so you can access it in other methods, too.
class CardCollectionList {
BaseballCard[] baseballCardList;
public CardCollectionList() {
baseballCardList = new BaseballCard[101];
}
public int size(){
int size = 0;
for(int i = 1; i<this.baseballCardList.length; i++) {
if (baseballCardList[i] != null) {
size+=1;
}
}
return size;
}
}
The code is as close to your fragment as possible. There are several ways to improve this (keep track of the size when adding, automatic array reallocation etc.). But it is a start if you want to try this yourself.
Normally, you'd probably just use ArrayList<BaseballCard>.
Now I need to make another class which would be my collection class.
... What would be the best way to do this.
I don't have enough reputation to comment on your question, so I am going to assume that you just want to store BaseballCard objects in a Java Collection. The Java SDK offers a lot of options. Since you are asking about the "best" way to go then I would use one of those unless you need to add additional functionality .
if you don't find what you need from the Java SDK or just want to create your own Collection then follow the advice given by #michał-szydłowski above
I am stuck in a very simple problem for more then 2 hours. I am trying to create a two dimensional array and fill it with a constructor. However, I couldn't pass this step.
public class Test
{
public State [][] test1= new State[4][3];//
public State test2[][]= new State[4][3];//
public State [][]test3;
public State test4[][];
public class State{
int position;
double reward;
int policy;
}
public Test(){
test1[1][1].position=1; // never worked
test2[1][3].position=2; //never worked
test3=new State[4][3];
test3[1][2].position=3; //never worked
test4=new State[4][3];
test4[2][2].position=4;//never worked
}
}
I am calling above function with following code
Test test= new Test();
Log.e("done","pass"); //I never reach here. the code always stuck on the constructor.
When you create the array :
public State [][] test1 = new State[4][3];
you are creating an array that can hold 4 * 3 State instances, but each position in the array is initialized to null.
You need to assign an instance of State to each position in the array before accessing it. If you don't, you'll get a NullPointerException.
For example :
public Test()
{
test1[1][1] = new State();
test1[1][1].position = 1;
....
}
I have to do my homework in Greenfoot.
This part means that I have to save the position of Chess and then click reset.
Then, I have to choose load to put back the pieces of chess in the position they had before reset.
Since I don't know the exact size of the array, I know I can use List but it isn't allowed in the homework.
Nothing showed up on the screen but there is no error message.
Assume I have a class called Chess.
static Actor[] allChess;
public void save() // this is the save
{
Actor[] allChess = GWorld.getAllObjects("Chess");
}
public void load() // this is the load
{
if (allChess != null)
{
for (int i=0; i < allChess.length; i++)
{
Chess ch = (Chess) allChess[i];
GWorld.addOneObject(new Chess(ch.color, ch.rank), ch.getX(), ch.getY());
}
}
}
Thanks a lot!
allChess is redeclared as a local variable in save(). Do like this :
public void save() // this is the save
{
allChess = GWorld.getAllObjects("Chess");
}
Ok, here is the code and then the discussion follows:
public class FlatArrayList {
private static ArrayList<TestWrapperObject> probModel = new ArrayList<TestWrapperObject>();
/**
* #param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
int [] currentRow = new int[10];
int counter = 0;
while (true) {
for (int i = 0; i < 10; i++) {
currentRow[i] = probModel.size();
}
TestWrapperObject currentWO = new TestWrapperObject(currentRow);
probModel.add(counter, currentWO);
TestWrapperObject testWO = probModel.get(counter);
// System.out.println(testWO);
counter++;
if (probModel.size() == 10) break;
}
// Output the whole ArrayList
for (TestWrapperObject wo:probModel) {
int [] currentTestRow = wo.getCurrentRow();
}
}
}
public class TestWrapperObject {
private int [] currentRow;
public void setCurrentRow(int [] currentRow) {
this.currentRow = currentRow;
}
public int [] getCurrentRow() {
return this.currentRow;
}
public TestWrapperObject(int [] currentRow) {
this.currentRow = currentRow;
}
}
What is the above code supposed to do? What I am trying to do is load an array as a member of some wrapper object (TestWrapperObject in our case). When I get out of the loop,
the probModel ArrayList has the number of elements it is supposed to have but all have the same value of the last element (an array of size 10 with each item equal to 9). This is not the case inside the loop. If you perform the same "experiment" with a primitive int value everything works fine. Am I missing something myself regarding arrays as object members? Or did I just encounter a Java bug? I am using Java 6.
You are only creating one instance of the currentRow array. Move that inside the row loop and it should behave more like you expect.
Specifically, the assignment in setCurrentRow does not create a copy of the object, but only assigns the reference. So each copy of your wrapper object will hold a reference to the same int[] array. Changing the values in that array will make the values appear to change for all other wrapper objects that hold a reference to the same instance of the array.
i don' t want to sound condescending, but always try to remember tip #26 from the excellent pragmatic programmer book
select isn't broken
it is very rare to find a java bug. keeping this in mind often helps me to look over my code again, turn it around, and shake out the loose bits until i finally discover where i was wrong. of course asking for help early enough is very encouraged, too :)