Question

我正在尝试将一个String类型的键和一个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，我无法弄清楚原因。

My entire class can be found here. But for brevity, I've narrowed it down to the problem parts below.

这是我的Treemap声明（我使用的是Java 7，所以它喜欢钻石。

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

这是我的方法的一部分（其余的与其他精灵做同样的事情，并在这里注释put（）方法稍后在另一个put（）方法中抛出另一个异常。

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，此处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";

}

Answer 1

在行

中有两个nullpointerexception选项

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

getPaneSprited（）返回null
settings.WELCOME_PANE_TYPE为空

要查看它是否为1，您可以将get call和put分成两行。然后在getter返回null时调试。

Treemap键可能不为null，因此也可以。它与泛型无关，因为一旦编译完成，由于类型擦除，泛型无论如何都会消失。

使用TreeMap和泛型的空指针异常

1 个答案: