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我正在尝试将 String 类型的键和 LinkedList 类型的值（它本身是 Sprite 类型）插入到 TreeMap 中。但是，当我的代码调用 put() 方法时，它会抛出一个空指针异常，我不知道为什么。

我的整个班级都可以在这里找到。但为简洁起见，我已将其范围缩小到以下问题部分。

这是我的 Treemap 声明（我使用的是 Java 7，所以它喜欢菱形。

TreeMap<String, LinkedList<Sprite>> paneSprites = new TreeMap<>();

这是我的方法的一部分（其余部分与其他精灵做同样的事情，在这里注释掉 put() 方法只是稍后在另一个 put() 方法处引发另一个异常。

public void initGUIControls()
{
    canvas = new RambleOnPanel(this, (RambleOnDataModel)data);
    LinkedList<Sprite> spriteList = new LinkedList<>();

    //Sprite for Welcome Pane
    SpriteType st = new SpriteType(settings.WELCOME_BACKGROUND_TYPE);
    BufferedImage img = loadImage(settings.WELCOME_IMAGE_PATH);
    st.addState(settings.DEFAULT_STATE, img);
    st.addState(settings.INVISIBLE_STATE, img);
    int x = 0;
    int y = 0;
    int vX = 0;
    int vY = 0;
    Sprite s = new Sprite(st,x,y,vX,vY, settings.DEFAULT_STATE);
    spriteList.add(s);
    guiButtons.put(st.getSpriteTypeID(), s);

    //put sprite types for this pane in the hash map and clear the list
    getPaneSprites().put(settings.WELCOME_PANE_TYPE, spriteList);  //EXCEPTION THROWN HERE
    spriteList.clear();

    //Sprites for Select Account Pane

此外，这里使用的所有字符串都在另一个类中实例化，如下所示

package ramble_on;

public class Settings
{
//Game Settings
public final String APP_TITLE = "Ramble On!";
public final int FRAME_RATE = 30;
public final int GAME_HEIGHT = 700;
public final int GAME_WIDTH = 1200;

//Sprite States
public final String INVISIBLE_STATE = "INVISIBLE STATE";
public final String  DEFAULT_STATE = "DEFAULT STATE";

//Pane Types
public final String WELCOME_PANE_TYPE = "WELCOME PANE TYPE";
public final String SELECT_ACCOUNT_PANE_TYPE = "SELECT ACCOUNT PANE TYPE";
public final String CURRENT_ACCOUNT_PANE_TYPE = "CUTTENT ACCOUNT PANE TYPE";

//Sprite Types
public final String WELCOME_BACKGROUND_TYPE = "WELCOME BACKGROUND TYPE";
public final String SELECT_ACCOUNT_BACKGROUND_TYPE = "SELECT ACCOUNT TYPE";
public final String NEW_USER_BUTTON_TYPE = "NEW USER BUTTON TYPE";
public final String CURRENT_ACCOUNT_BACKGROUND_TYPE = "CURRENT ACCOUNT BACKGROUND TYPE";
public final String LARGE_RETURN_BUTTON_TYPE = "LARGE RETURN BUTTON TYPE";

//Sprite Image paths
public   final String IMAGES_PATH = "./data/images/";

public final String WELCOME_IMAGE_PATH = IMAGES_PATH + "welcome.png";
public final String SELECT_ACCOUNT_BACKGROUND_IMAGE_PATH = IMAGES_PATH + "selectAccount.png";
public final String NEW_USER_BUTTON_PATH = IMAGES_PATH + "newUser.png";
public final String Current_Account_SCREEN_BACKGROUND_IMAGE_PATH = IMAGES_PATH + "currentAccount.png";
public final String LARGE_RETURN_BUTTON_IMAGE_PATH = IMAGES_PATH + "newUser.png";

}
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1 回答 1

1

对于该行中的 nullpointerexception，您有两个选项

getPaneSprites().put(settings.WELCOME_PANE_TYPE, spriteList);

  1. getPaneSprited() 返回 null
  2. settings.WELCOME_PANE_TYPE 为空

要查看它是否为 1，您可以将 get 调用和 put 拆分为两条不同的行。然后调试 getter 是否返回 null。

树形图键可能不为空，因此也可能为空。它与泛型无关，因为一旦编译，泛型就会由于类型擦除而消失。

于 2013-04-14T13:45:10.363 回答