初始化2D Java数组

Question

I am working on an extremely basic game. However when I try to create the array i am running into errors. The error is index out of bounds. However I thought I fixed it by adding the -1 to make sure I don't go out of bounds. can someone tell me, or give me a clue as to what I did wrong?

package gameProject;

public class world {
int numEnemies, numBosses;
int [][] world = new int[10][10];

public world(){
    int[][] world  = createArray(10,10);
    populateWorld(world);
}

private int[][] createArray(int inX, int inY){
    //create the array that holds world values
    int[][] world = new int[inX][inY];
    //initialize the world array
    for(int i = 0; i < world.length - 1; i ++){
        for(int j = 0; j < world[0].length - 1; j++){
            world[i][j] = 0;
        }
    }

    return world;
}

private void populateWorld(int[][] world){
    for(int i = 0; i < world.length - 1; i++){
        for(int j = 0; j < world[0].length - 1; i++){
            world[i][j] = 0;
        }
    }

}
}

Answer 1

In your populateWorld method, change

for(int j = 0; j < world[0].length - 1; i++)

to

for(int j = 0; j < world[0].length - 1; j++)

You keep incrementing the wrong counter, going eventually out of its bounds. (10)

( PS: you don't need the length - 1 in your loops' condition, just length would do)

Answer 2

The error is in

for (int j = 0; j < world[0].length - 1; i++)

you should write

for (int j = 0; j < world[0].length - 1; j++)

instead.

Note that you can reduce your code a little bit:

You create the array for member World.world twice. Also the elements of an int array are already initialized to 0 so you don't need to do this explicitly.

Answer 3

You should just do

private int[][] createArray(int inX, int inY) {
    int[][] world = new int[inX][inY];
    for (int i = 0; i < inX; i++)
        for (int j = 0; j < inY; j++)
            world[i][j] = 0;
    return world;
}

You never actually need to check the length of the world array, because the length was already passed in as a parameter value.

And then also

private void populateWorld(int[][] world) {
    for (int i = 0; i < world.length; i++)// v     error 'i' should be 'j'
        for (int j = 0; j < world[i].length; j++) // <- error on this line
            world[i][j] = 0;
}

Answer 4

Your basic problem is that you're incrementing the wrong loop variable. Why? Because you're far off from any clean code. Lemme show you how clean coding is done:

• class names start with a capital letter, method and variable name with lower case letters
• you might prefix your variables with their scope ('m' for member, 'p' for parameter, nothing for local variables). Saves you the all-time-reference to 'this'. Strongly depends on your code style. I highly suggest doing it, keeps your code clean and really easy to debug.
• use the final and private keywords where possible
• use descriptive variable names. Here especially x and y for loop variables, as you're abstracting a 2d-plane

Some more considerations:

• usually games grow more complex. Usually simple primitives (like your int-array) will not suffice for long to store all relevant information. Use classes like Cell
• use enums so you can lose magic numbers => coding, reading and debugging made a lot easier

So - after a lot of talk - here's the final code:

package gameproject;

/**
 * Use comments like this to describe what the classes purpose is.
 * Class comment is the most important one. If you can't tell what a method/variable is doing by its name, you should also comment methods and/or variables!
 * @author JayC667
 */
public class World {

    /*
     * STATIC part of the class - keep separated from object code
     */

    // you could/should also put these static classes to their separate files and make em non-static
    /**
     * Denotes, what a {@linkplain Cell} is occupied with
     */
    static public enum CellType {
        EMPTY, //
        BOSS, //
        ENEMY
    }

    /**
     * Represents a single cell within the world. Stores information about its coodrinates (redundant) and its occupator (see {@linkplain CellType})
     * @author JayC667
     */
    static private class Cell { // use cell to store data for you
        public final int    mX;                         // x and y are actually not useful at the moment, you could also remove them
        public final int    mY;
        private CellType    mCellType   = CellType.EMPTY;

        public Cell(final int pX, final int pY) {
            mX = pX;
            mY = pY;
        }

        public CellType getCellType() {
            return mCellType;
        }
        public void setCellType(final CellType pCellType) {
            mCellType = pCellType;
        }
    }

    // when possible, make methods static, unless you unnecessarily blow up the parameter list
    // this is a typical demo for a factory method
    static private Cell[][] createWorld(final int pWidth, final int pHeight) {
        final Cell[][] newWorld = new Cell[pWidth][pHeight];
        for (int y = 0; y < pHeight - 1; y++) {
            for (int x = 0; x < pWidth - 1; x++) {
                newWorld[y][x] = new Cell(x, y);
            }
        }
        return newWorld;
    }

    /*
     * OBJECT part of the class - keep separated from static code
     */

    private final Cell[][]  mWorld;
    private final int       mWorldWidth;
    private final int       mWorldHeight;
    private final int       mNumberOfEnemies;
    private final int       mNumberOfBosses;

    public World(final int pWidth, final int pHeight, final int pNumberOfEnemies, final int pNumberOfBosses) {
        if (pWidth < 1 || pHeight < 1) throw new IllegalArgumentException("World width and height must be greater than 0!");
        if (pNumberOfEnemies < 0 || pNumberOfBosses < 0) throw new IllegalArgumentException("Enemy and boss counts must not be negative!");
        if (pWidth * pHeight < pNumberOfEnemies + pNumberOfBosses) throw new IllegalArgumentException("World is too small for all the bad guys!");

        mWorldWidth = pWidth;
        mWorldHeight = pHeight;
        mNumberOfEnemies = pNumberOfEnemies;
        mNumberOfBosses = pNumberOfBosses;
        mWorld = createWorld(pWidth, pHeight);
        populateWorld();
    }

    // refers to many member variables, so not static (would only blow up parameter list)
    private void populateWorld() {
        for (int i = 0; i < mNumberOfBosses; i++) {
            final Cell c = getRandomCell(CellType.EMPTY);
            mWorld[c.mY][c.mX].setCellType(CellType.BOSS);
        }
        for (int i = 0; i < mNumberOfEnemies; i++) {
            final Cell c = getRandomCell(CellType.EMPTY);
            mWorld[c.mY][c.mX].setCellType(CellType.ENEMY);
        }
    }

    private Cell getRandomCell(final CellType pCellType) {
        while (true) { // TODO not a good, but simple solution; might run infinite loops
            final int randomX = (int) (mWorldWidth * Math.random());
            final int randomY = (int) (mWorldHeight * Math.random());
            if (mWorld[randomY][randomX].getCellType() == pCellType) return new Cell(randomX, randomY);
        }
    }

}