java - 无法实例化

Question

我一直在尝试创建一个用于我们的 java 游戏的 Sprite 。一切看起来都很正常，我的程序没有看到任何错误，但是当它运行时突然出现错误，无法实例化。有人能告诉我这是怎么回事吗？

@SuppressWarnings("unused")
public class TrueSprite
{
BufferedImage spriteSheet = ImageIO.read(new File("robin.png"));

int width = 240, height = 314, rows = 5 , columns = 5;

BufferedImage[] sprites = new BufferedImage[rows * columns];

public TrueSprite(int width, int height, int rows, int columns) throws IOException
{
    this.width = width;
    this.height = height;
    this.rows = rows;
    this.columns = columns;

    for(int i = 0; i < rows; i++)
    {
        for(int j = 0; j < columns; j++)
        {
            sprites[(i * columns) + j ] = spriteSheet.getSubimage(i * width, j * height, width, height);
        }
    }

}

public void paint(Graphics g)
{
    g.drawImage(sprites[1], 100, 100, null);
}


}

错误如下:

load: really.sprite.TrueSprite.class can't be instantiated.
java.lang.InstantiationException: really.sprite.TrueSprite
at java.lang.Class.newInstance(Unknown Source)
at sun.applet.AppletPanel.createApplet(Unknown Source)
at sun.applet.AppletPanel.runLoader(Unknown Source)
at sun.applet.AppletPanel.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)

Answer 1

首先，您没有构造函数，这对于实例化您的类至关重要。将其放入类声明中:

public TrueSprite() {
    //code to run when your class is instantiated.
}

现在，这不会做任何特别的事情，但你可以用以下方式调用它:

TrueSprite sprite = new TrueSprite();

此外，你的类(class)需要清理。尝试将赋值代码放入我们刚刚构建的构造函数中，并将这些变量的声明置于其外部:

@SuppressWarnings("unused")
public class TrueSprite
{
    private final int width;
    private final int height;
    private final int rows;
    private final int cols;
    private BufferedImage bigImg;
    private BufferedImage[] sprites;

    public TrueSprite(int width, int height, int rows, int columns) {
        this.width = width;
        this.height = height;
        this.rows = rows;
        this.cols = columns;
        this.bigImg = ImageIO.read(new File("robin.png"));
        this.sprites = new BufferedImage[rows * cols];

        for (int i = 0; i < rows; i++) {
            for (int j = 0; j < cols; j++) {
                sprites[(i * cols) + j] = bigImg.getSubimage(j * width, i * height, width, height);    
            }
        }
    }

    public void paint(Graphics g)
    {
        g.drawImage(sprites[1], 100, 100, null);
    }
}

只需确保将四个有效参数传递到 TrueSprite 构造函数中即可正确调用它:

TrueSprite sprite = new TrueSprite(200, 500, 20, 50);