java - 抽象类和子类中的静态变量初始化

Question

我是错误处理的新手。我在变量初始化方面遇到麻烦。只要存在图片，它就可以正常工作，但是当我故意加载不正确的路径时，我在下面收到以下错误消息。

所以我的猜测是，如果我正确地修复了静态方法的初始化，那么问题将得到解决。

    Exception in thread "main" java.lang.ExceptionInInitializerError
at Board.placeBishops(Board.java:149)
at Board.createNewBoard(Board.java:64)
at RunGame.main(RunGame.java:19)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:497)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)


    Caused by: java.lang.IllegalArgumentException: input == null!
at javax.imageio.ImageIO.read(ImageIO.java:1388)
at Bishop.<clinit>(Bishop.java:24)


public class Bishop extends Piece{
private static BufferedImage whiteBishopImage;
private static BufferedImage blackBishopImage;

static {
try {
    whiteBishopImage = ImageIO.read(ChessFrame.class.getResource("/resources/icons/bishop_white.png"));
    blackBishopImage = ImageIO.read(ChessFrame.class.getResource("resources/icons/bishop_black.png"));
}
catch (IOException e) {
    e.printStackTrace();
    whiteBishopImage = warningImage;
    blackBishopImage = warningImage;
    RunGame.getLogger().log(Level.WARNING, "Failed to load Bishop image");
}


}
@Override public BufferedImage getImage() {
if (color == PieceColor.WHITE){
    return whiteBishopImage;
}
else return blackBishopImage;
}

这是抽象类。

public abstract class Piece {
protected static BufferedImage warningImage;
protected static BufferedImage myImage;


static {
try {
    warningImage = ImageIO.read(ChessFrame.class.getResource("/resources/icons/warning.png"));

} catch (IOException e) {
    e.printStackTrace();
    JOptionPane.showMessageDialog(null, "Failed to load warning image, application will be shutdown");
    RunGame.getLogger().log(Level.WARNING, "Failed to load warning image, application was shutdown");
    System.exit(1);
}
myImage = warningImage;
}   
public BufferedImage getImage(){
return myImage;
}

Answer 1

您的代码中的问题是您仅在初始化程序中捕获了IOException，但没有捕获NullPointerException。这可能是由于以下事实:检查IOException而未检查NullPointerException，因此您的IDE不会告诉您它可能在此处发生。

背景:不存在的资源上的Class.getResource()将返回null，并且由于不检查其结果，因此将null传递给ImageIO.read，这会引起咳嗽。

因此，您有以下选择(如果您想坚持使用初始化程序，那就是...)

捕获NullPointerException以及IOException:

try {
    warningImage = ImageIO.read(ChessFrame.class.getResource("/resources/icons/warning.png"));
} catch (IOException | NullPointerException e) {
    e.printStackTrace();
    JOptionPane.showMessageDialog(null, "Failed to load warning image,application will be shutdown");
    RunGame.getLogger().log(Level.WARNING, "Failed to load warning image, application was shutdown");
    System.exit(1);
}

或先检查getResource的结果:

try {
    URL imageResource = ChessFrame.class.getResource("/resources/icons/warning.png");
    if(imageResource != null) {
        warningImage = ImageIO.read(imageResource);
    } else {
        // do something useful
    }
} catch (IOException  e) {
    e.printStackTrace();
    JOptionPane.showMessageDialog(null, "Failed to load warning image,application will be shutdown");
    RunGame.getLogger().log(Level.WARNING, "Failed to load warning image, application was shutdown");
    System.exit(1);
}