Develop Reference

2D array of objects returns null

Code creating object array and toString method.
import java.util.Arrays;
public class TicTacToeBoard extends BoardClass{
private int turns;
private XOClass[][] a;
public TicTacToeBoard(int rows,int cols){
super(rows,cols);
XOClass[][]a = new XOClass[rows][cols];
turns = 0;
}
public String toString(){
return (Arrays.deepToString(a));
}
}
Object Class
public class XOClass{
private String name;
private static int turn=0;
public XOClass(){
if (turn==0){
this.name = "-";
}
if (turn==1){
this.name = "X";
}
else{
this.name = "O";
}
}
Demo Class
public class play {
public static void main(String[] args){
TicTacToeBoard tac = new TicTacToeBoard(3,3);
System.out.println(tac);
}
}
when calling class play it returns null as there is nothing in the array what am I doing wrong with my code.

In your code:
XOClass[][]a = new XOClass[rows][cols];
You initialize new XOClass its only in the method and when the method end it is distrusting.
change that to
a = new XOClass[rows][cols];
This means you have created a two-dimensional array, with 'rows' rows. In the first row there are 'cols' columns.
and all rows are null.
Now you should create rows like :
a[0] = new XOClass[cols];
And then
a[0][0]=new XOClass();

Calling another Method from object-Java

I'm stumped. I created a method called "makeBed" in the (BedRoom) class that calls another method in the (Bed) class called "make". But when I try to call the method via bedroom.makeBed(); it does not work. I put a // in the part i'm trying to get to work.
Main
public class Main {
Wall wall1 = new Wall("West");
Wall wall2 = new Wall("East");
Wall wall3 = new Wall("South");
Wall wall4 = new Wall("North");
Ceiling ceiling = new Ceiling(12, 55);
Bed bed = new Bed("Modern", 4, 3, 2, 1);
Lamp lamp = new Lamp("classic", false, 75);
BedRoom bedroom = new BedRoom("test",wall1,wall2,wall3,wall4,ceiling,bed,lamp);
bedroom.makeBed(); //bedroom.makeBed(); does not work
//It does not show the public method "makeBed" in the BedRoom class
}
BedRoom Class
public class BedRoom {
private String name;
private Wall wall1;
private Wall wall2;
private Wall wall3;
private Wall wall4;
private Ceiling ceiling;
private Bed bed;
private Lamp lamp;
public BedRoom(String name, Wall wall1, Wall wall2, Wall wall3, Wall wall4, Ceiling ceiling, Bed bed, Lamp lamp) {
this.name = name;
this.wall1 = wall1;
this.wall2 = wall2;
this.wall3 = wall3;
this.wall4 = wall4;
this.ceiling = ceiling;
this.bed = bed;
this.lamp = lamp;
}
public Lamp getLamp(){
return this.lamp;
}
public void makeBed(){ //This is the method I'm trying to access
System.out.println("Bedroom -> Making bed");
bed.make();
}
}
Bed Class
public class Bed {
private String style;
private int pillows;
private int height;
private int sheets;
private int quilt;
public Bed(String style, int pillows, int height, int sheets, int quilt) {
this.style = style;
this.pillows = pillows;
this.height = height;
this.sheets = sheets;
this.quilt = quilt;
}
public void make(){
System.out.println("Bed -< Making"); //Method I'm trying to call
}
public String getStyle() {
return style;
}
public int getPillows() {
return pillows;
}
public int getHeight() {
return height;
}
public int getSheets() {
return sheets;
}
public int getQuilt() {
return quilt;
}
}

I want to say this is it... You don't have your code wrapped into a method so it not compiling right.
public class Main {
public static void main(String[] args) {
Wall wall1 = new Wall("West");
Wall wall2 = new Wall("East");
Wall wall3 = new Wall("South");
Wall wall4 = new Wall("North");
Ceiling ceiling = new Ceiling(12, 55);
Bed bed = new Bed("Modern", 4, 3, 2, 1);
Lamp lamp = new Lamp("classic", false, 75);
BedRoom bedroom = new BedRoom("test",wall1,wall2,wall3,wall4,ceiling,bed,lamp);
bedroom.makeBed(); //bedroom.makeBed(); does not work
//It does not show the public method "makeBed" in the BedRoom class
}
}
Maybe that will work.
This is on the assumption that THIS is your class you want to initilize the whole script from, if not change public static void main(String[] args){} into public Main() {}

Java Object Array Initialization

I am working on a java project which contains 3 classes and an object array in one of the classes. This project is ultimately supposed to move 4 entity objects around on a board by using the coordinates of the entity objects. These entity objects are stored in an array in the world class. My problem is with the array initialization in the world class. I am not sure how to set each element of the array equal to an object from the entity class and then access that object's coordinates to move it around on the board. The coordinates for the entity objects are initially set at 20x30 in a default constructor. Here is my code:
public class entity {
private int xcoordinate;
private int ycoordinate;
private String name;
private char symbol;
public entity(){
xcoordinate = 20;
ycoordinate = 30;
}
private entity(int newxcoor, int newycoor, String newname, char newsymbol){
xcoordinate = newxcoor;
ycoordinate = newycoor;
name = newname;
symbol = newsymbol;
}
public int getXCoor(){
return xcoordinate;
}
public int getYCoor(){
return ycoordinate;
}
}
public class world {
private entity[] ObArray = new entity[4];
public world(){
world test = new world();
}
public void draw(){
for (int i = 0; i < 4; i++)
{
//int x = ObArray[i].getXLoc();
//int y = ObArray[i].getYLoc();
}
}
}
public class mainclass {
public static void main(String[] args){
world worldob = new world();
//entity a = new entity();
//entity b = new entity();
//entity c = new entity();
//entity d = new entity();
worldob.draw();
}
}
My draw function and main function are not finished. After the array is initialized I will be able to finish the draw method using the entity get functions.
Thanks for your help.

That is one way of doing it. You can also define all of your entities inline like this:
private entity[] ObArray = {
new entity(0,0,"Entity1",'a'),
new entity(10,10,"Entity2",'b'),
new entity(20,20,"Entity3",'c'),
new entity(30,30,"Entity4",'d')
};
A better way may be to do an ArrayList instead of an array:
private List<entity> ObArray = new ArrayList<>();
ObArray.add(new entity(0,0,"Entity1",'a');
ObArray.add(new entity(10,10,"Entity2",'b');
ObArray.add(new entity(20,20,"Entity3",'c');
ObArray.add(new entity(30,30,"Entity4",'d');
To access each element you just need to get the element from the array and either get or set the properties you need:
ObArray[0].getXCoor();
ObArray[0].setXCoor(5);

Your problem is only creating new object of world inside world's constructor which throws stack overflow error, otherwise it is fine:
public world(){ world test = new world(); //REMOVE THIS LINE
}

You simply need to initialise the array. This can be done in the world constructor.
public world()
{
for (int i = 0; i < 4; i++)
{
ObArray[i] = new entity();
}
}
Then you can access the objects in your draw method, as you've shown:
public void draw()
{
for (int i = 0; i < 4; i++)
{
int x = ObArray[i].getXCoor();
int y = ObArray[i].getYCoor();
System.out.println("x" + x);
System.out.println("y" + y);
// Manipulate items in the array
// ObArray[i].setXCoor(10);
}
}
A more complete example, with the move functions added, and the class names capitalised:
public class Entity
{
private int xcoordinate;
private int ycoordinate;
private String name;
private char symbol;
public Entity()
{
xcoordinate = 20;
ycoordinate = 30;
}
private Entity(int newxcoor, int newycoor, String newname, char newsymbol)
{
xcoordinate = newxcoor;
ycoordinate = newycoor;
name = newname;
symbol = newsymbol;
}
public int getXCoor()
{
return xcoordinate;
}
public void setXCoor(int xcoordinate)
{
this.xcoordinate = xcoordinate;
}
public int getYCoor()
{
return ycoordinate;
}
public void setYcoor(int ycoordinate)
{
this.ycoordinate = ycoordinate;
}
public static void main(String[] args)
{
World worldob = new World();
worldob.draw();
worldob.move(0, 15, 30);
worldob.move(1, 45, 0);
worldob.move(2, 23, 27);
worldob.move(3, 72, 80);
worldob.draw();
}
}
class World
{
private final Entity[] ObArray;
public World()
{
this.ObArray = new Entity[4];
for (int i = 0; i < ObArray.length; i++)
{
ObArray[i] = new Entity();
}
}
public void move(int index, int xCoor, int yCoor)
{
if (index >= 0 && index < ObArray.length)
{
Entity e = ObArray[index];
e.setXCoor(xCoor);
e.setYcoor(yCoor);
}
}
public void draw()
{
for (Entity e : ObArray)
{
int x = e.getXCoor();
int y = e.getYCoor();
System.out.println("x" + x);
System.out.println("y" + y);
}
}
}

Java object scope, referencing from a method

I'm having some trouble getting scope right in my head. I understand why the code below won't work, but I don't understand conceptually how I should be doing it.
public class Game {
private String playerName = "";
private int numberOfPegs = 0;
private boolean gameRunning = "True";
public static void main(String[] args) {
Game game = new Game();
game.setupGame();
game.playGame();
}
public void setupGame() {
Display display = new Display();
Code code = new Code();
display.showGreeting();
playerName = display.getUserInput("Enter your name: ");
numberOfPegs = Integer.parseInt(display.getUserInput("How many pegs would you like?"));
code.generateNewCode(numberOfPegs);
}
public void playGame() {
String result = display.getGuess();
}
}
I know why I can't call display.getGuess() from playGame(), it's because display is out of scope. I don't understand how to do this correctly. Do I create a new instance Display() for that method, that just doesn't feel like it's correct. I feel like I'm missing a Object Oriented concept when it comes to working with multiple objects.

Set the display as an instance field, and then initialize it in the setupGame() method.
private String playerName = "";
private int numberOfPegs = 0;
private boolean gameRunning = "True";
private Display display;
public static void main(String[] args) {
Game game = new Game();
game.setupGame();
game.playGame();
}
public void setupGame() {
display = new Display();
Code code = new Code();
display.showGreeting();
playerName = display.getUserInput("Enter your name: ");
numberOfPegs = Integer.parseInt(display.getUserInput("How many pegs would you like?"));
code.generateNewCode(numberOfPegs);
}
public void playGame() {
String result = display.getGuess();
}
There's no need to instantiate a member when you declare it. When you declare a member without instantiating, it takes its default value; 0 for numeric types, false for boolean and null for Object types. So in this case,
private int numberOfPegs = 0;
Would be the same as:
private int numberOfPegs;

Creating global array of objects (java)

So I'm working on a Space Invaders theme project, and I have most of my classes up and running and have started on the animation. Part of the process is the ship's weapons.
I have a class for the weapons, as below (Focus on the constructor):
/**
* #(#)Weapon.java
*
*
* #author Tristan Nel - 18179460
* #version 1.00 2015/3/4
*/
public class Weapon {
private String type;
private int damage;
private int rof; //rate of fire
private int orientation;
private int firingStage; //0 - not firing ; 1 - flash & recoil ; 2 - bullet
private String[] sprites; //Set of sprite image file names
public Weapon() {
}
public Weapon(String type, int damage, int rof, int orientation, int firingStage, String[] sprites)
{
this.type = type;
this.damage = damage;
this.rof = rof;
this.orientation = orientation;
this.firingStage = firingStage;
this.sprites = sprites;
}
//GET and SET Methods
public void setType(String type)
{
this.type = type;
}
public void setDamage(int damage)
{
this.damage = damage;
}
public void setROF(int rof)
{
this.rof = rof;
}
public void setOrientation(int orientation)
{
this.orientation = orientation;
}
public void setFiringStage(int firingStage)
{
this.firingStage = firingStage;
}
public void setSprites(String[] sprites)
{
this.sprites = sprites;
}
public String getType()
{
return this.type;
}
public int getDamage()
{
return this.damage;
}
public int getROF()
{
return this.rof;
}
public int getOrientation()
{
return this.orientation;
}
public int getFiringStage()
{
return this.firingStage;
}
public String[] getSprites()
{
return this.sprites;
}
}
In another class, which handles all elements on the game screen to be animated, I want to have a global array of hardcoded Weapon types that can be accessed as needed without fuss. I have attempted to do so at the top of the contents of the class:
/**
* #(#)GameScreen.java
*
*
* #author Tristan Nel - 18179460
* #version 1.00 2015/3/4
*/
import java.util.Scanner;
import java.io.*;
public class GameScreen {
private static final String HIGH_SCORE_FILE = "highScore.txt";
//Available Weapons
//UPDATED SINCE ORIGINAL POST
public static final Weapon[] WEAPONS = new Weapon[4];
WEAPONS[0] = new Weapon("Machinegun", 10, 20, 0, 0, {Graphics.MG_L_NORM, Graphics.MG_R_NORM});
WEAPONS[1] = new Weapon("Plasma MG", 20, 20, 0, 0, {Graphics.PMG_L_NORM, Graphics.PMG_R_NORM});
WEAPONS[2] = new Weapon("Photon Cannon", 40, 5, 0, 0, {Graphics.PC_L_NORM, Graphics.PC_R_NORM});
WEAPONS[3] = new Weapon("Alien Destabilizer", 60, 10, 0, 0, {Graphics.AD_L_NORM, Graphics.AD_R_NORM});
private Ship defender;
private Weapon equipped;
//private Invader[] aliens;
//private Bullet[] bullets;
private int score;
private int highscore;
private int lives;
public GameScreen() {
}
public GameScreen(Ship defender, int score, int lives)
{
this.defender = defender;
this.score = score;
this.lives = lives;
}
public void loadHighscore()
{
try
{
Scanner sc = new Scanner(new File(HIGH_SCORE_FILE));
this.highscore = Integer.parseInt(sc.next());
sc.close();
}
catch(FileNotFoundException fnf)
{
System.out.println(fnf);
this.highscore = 0;
}
}
public void saveHighScore(int highscore)
{
try
{
FileWriter write = new FileWriter(HIGH_SCORE_FILE);
PrintWriter pw = new PrintWriter(write);
pw.print(this.highscore);
pw.close();
}
catch(IOException e)
{
System.out.println(e);
}
}
//GET and SET methods
public void setDefender(Ship defender)
{
this.defender = defender;
}
public void setScore(int score)
{
this.score = score;
}
public void setLives(int lives)
{
this.lives = lives;
}
public Ship getDefender()
{
return this.defender;
}
public int getScore()
{
return this.score;
}
public int getLives()
{
return this.lives;
}
}
This gives me the following error messages on each line that I try to add another element to the array:
UPDATED
https://drive.google.com/file/d/0B7ye7Ul2JDG2NDFDRTJNM1FCd0U/view?usp=sharing
It is highly frustrating..
I read somewhere that you have to create an object within a method? (Eg. main() )
But I tried that in my driver class and it made no difference...
Will appreciate any help/advice (:

There are multiple issues
You cannot have arbitrary code in the body of your class, e.g. the WEAPONS[0] = calls. However, you can initialize the array directly using new Type[]{} syntax. You could also use a static initializer static {} but this is not recommended.
Also, you need to use the constructor via new keyword, it's not just a method, i.e. new Weapon() not Weapon()
You cannot declare arrays using {}, i.e. new String[]{{Graphics.MG_L_NORM, Graphics.MG_R_NORM}} not {Graphics.MG_L_NORM, Graphics.MG_R_NORM}
Working version
public static final Weapon[] WEAPONS = new Weapon[] {
new Weapon("Machinegun", 10, 20, 0, 0, new String []{Graphics.MG_L_NORM, Graphics.MG_R_NORM}),
new Weapon("Plasma MG", 20, 20, 0, 0, new String []{Graphics.PMG_L_NORM, Graphics.PMG_R_NORM}),
new Weapon("Photon Cannon", 40, 5, 0, 0, new String []{Graphics.PC_L_NORM, Graphics.PC_R_NORM}),
new Weapon("Alien Destabilizer", 60, 10, 0, 0, new String []{Graphics.AD_L_NORM, Graphics.AD_R_NORM})
};

Actually I put it wrongly before but it looks like you need to call the constructor using the new operator like this.
arrayName[0] = new Weapon();

Since those classes seem somewhat static, something else to look into is using enums for this. This will help avoid complications when you have to search for a particular Weapon. A better design would be to have a WeaponType enum containing all the static immutable data in relation to a Weapon and have the Weapon class contain all the state data.