I'm working on a project for an intro to programming class, and I've run into a slight problem. We're making a side scroller, and I'm working on the score counter right now. My issue is that when I try to create a reference to the counter class in anything other than the act method(called once every frame) I get a null pointer exception error. You can download the zip file with my code in it here if you want to take a look.
EDIT:
Here's the offending code:
public class HeroMissile extends Missiles
{
/**
* Act - do whatever the HeroMissile wants to do. This method is called whenever
* the 'Act' or 'Run' button gets pressed in the environment.
*/
public void act()
{
move(8);
remove();
}
public void remove() {
if(isTouching(Drone.class)) {
removeTouching(Drone.class);
getWorld().addObject(new Explosion(), getX(), getY());
getWorld().removeObject(this);
addScore();
return;
}
}
public void addScore() {
City cityWorld = (City) getWorld();
**Counter scoreCounter = cityWorld.getCounter();**
scoreCounter.add(1);
}
}
You are calling getWorld() [in addScore()] after you removed yourself from the world. In this case, getWorld() will return null, so you will get a null pointer exception. Try changing the order in remove() to add the score before you remove yourself from the world.
Related
My test code to excercise various functions of JavaParser:
public class test001 {
public static void main(String[] args) {
test001 t = new test001();
t.run();
}
#sample.mkGetSet
int g1;
#sample.start
test001(){
g1 = 14;
}
#sample.funky
void run() {
#sample.flagVar
int a,b,c;
a=1;
b=2;
c=a+b;
c=c+g1;
System.out.println("result:"+c);
}
}
My code correctly notes that I call println in the method run.
Is there a fairly easy way to get the 'System.out.' part in addition to the println part?
In the case where the qualification is not there, I dont need it but if it is i would like it.
The type of answer I'm looking for is along the line of 'In the MethodCallExpr look at XXXXX' (with the obligatory admonition to RTFD)
I've been over the documentation and its still not clear how to do this - or if i even can.
I'm creating a mod for Minecraft. Recently, I've tried to make a custom block, and I'm having two issues with it.
My main issue is that the block is rendering incorrectly. I want the block to be smaller in size than a full block. I successfully changed the block boundaries with setBlockBounds(), and while that did make the block render smaller and use the smaller boundaries, it causes other rendering issues. When I place the block, the floor below is becomes invisible and I can see through it, either to caves below, blocks behind it, or the void if there is nothing there. How do I fix that block not rendering? Here's a screenshot:
Additionally, my goal for this block is to emit an "aura" that gives players around it speed or some other potion effect. I have the basic code for finding players around the block and giving them speed, but I can't find a way to activate this method every tick or every X amount of ticks to ensure that it gives players within the box speed in a reliable manner. There are already some blocks in the normal game that do this, so it must be possible. How can I do this?
For your first issue, you need to override isOpaqueCube to return false. You'll also want to override isFullCube for other parts of the code, but that isn't as important for rendering. Example:
public class YourBlock {
// ... existing code ...
/**
* Used to determine ambient occlusion and culling when rebuilding chunks for render
*/
#Override
public boolean isOpaqueCube(IBlockState state) {
return false;
}
#Override
public boolean isFullCube(IBlockState state) {
return false;
}
}
Here's some info on rendering that mentions this.
Regarding your second problem, that's more complicated. It's generally achieved via a tile entity, though you can also use block updates (which is much slower). Good examples of this are BlockBeacon and TileEntityBeacon (for using tile entities) and BlockFrostedIce (for block updates). Here's some (potentially out of date) info on tile entities.
Here's an (untested) example of getting an update each tick this with tile entities:
public class YourBlock {
// ... existing code ...
/**
* Returns a new instance of a block's tile entity class. Called on placing the block.
*/
#Override
public TileEntity createNewTileEntity(World worldIn, int meta) {
return new TileEntityYourBlock();
}
}
/**
* Tile entity for your block.
*
* Tile entities normally store data, but they can also receive an update each
* tick, but to do so they must implement ITickable. So, don't forget the
* "implements ITickable".
*/
public class TileEntityYourBlock extends TileEntity implements ITickable {
#Override
public void update() {
// Your code to give potion effects to nearby players would go here
// If you only want to do it every so often, you can check like this:
if (this.worldObj.getTotalWorldTime() % 80 == 0) {
// Only runs every 80 ticks (4 seconds)
}
}
// The following code isn't required to make a tile entity that gets ticked,
// but you'll want it if you want (EG) to be able to set the effect.
/**
* Example potion effect.
* May be null.
*/
private Potion effect;
public void setEffect(Potion potionEffect) {
this.effect = potionEffect;
}
public Potion getEffect() {
return this.effect;
}
#Override
public void readFromNBT(NBTTagCompound compound) {
super.readFromNBT(compound);
int effectID = compound.getInteger("Effect")
this.effect = Potion.getPotionById(effectID);
}
public void writeToNBT(NBTTagCompound compound) {
super.writeToNBT(compound);
int effectID = Potion.getIdFromPotion(this.effect);
compound.setInteger("Effect", effectID);
}
}
// This line needs to go in the main registration.
// The ID can be anything so long as it isn't used by another mod.
GameRegistry.registerTileEntity(TileEntityYourBlock.class, "YourBlock");
In my title screen, i have a code saying that the first controller using A is the PlayerIndex.one.
Here is the code:
public override void HandleInput(InputState input)
{
for (int anyPlayer = 0; anyPlayer <4; anyPlayer++)
{
if (GamePad.GetState((PlayerIndex)anyPlayer).Buttons.A == ButtonState.Pressed)
{
FirstPlayer = (PlayerIndex)anyPlayer;
this.ExitScreen();
AddScreen(new Background());
}
}
}
My question is: How can i use the "FirstPlayer" in other classes? (without this, there is no interest in this code)
I tried the Get Set thing but i can't make it work. Does i need to put my code in another class? Do you use other code to make this?
Thanks.
You can make a static variable say : SelectedPlayer,
and assign first player to it!
then you can call the first player through this class,
for example
class GameManager
{
public static PlayerIndex SelectedPlayer{get;set;}
..
..
..
}
and right after the loop in your code, you can say:
GameManager.SelectedPlayer = FirstPlayer;
I hope this helps, if your code cold be clearer that would be easier to help :)
Ok, so to do this properly you're going to have to redesign a little.
First off, you should be checking for a new gamepad input (i.e. you should be exiting the screen only when 'A' has been newly pressed). To do this you should be storing previous and current gamepad states:
private GamePadState currentGamePadState;
private GamePadState lastGamePadState;
// in your constructor
currentGamePadState = new GamePadState();
lastGamePadState = new GamePadState();
// in your update
lastGamePadState = currentGamePadState;
currentGamePadState = GamePad.GetState(PlayerIndex.One);
Really what you need to do is modify your class that deals with input. The basic functionality from your HandleInput function should be moved into your input class. Input should have a collection of functions that test for new/current input. For example, for the case you posted:
public Bool IsNewButtonPress(Buttons buton)
{
return (currentGamePadState.IsButtonDown(button) && lastGamePadState.IsButtonUp(button));
}
Then you can write:
public override void HandleInput(InputState input)
{
if (input.IsNewButtonPress(Buttons.A)
{
this.ExitScreen();
AddScreen(new Background());
}
}
Note: this will only work for one controller. To extend the implementation, you'll need to do something like this:
private GamePadState[] currentGamePadStates;
private GamePadState[] lastGamePadStates;
// in your constructor
currentGamePadStates = new GamePadState[4];
currentGamePadStates[0] = new GamePadState(PlayerIndex.One);
currentGamePadStates[1] = new GamePadController(PlayerIndex.Two);
// etc.
lastGamePadStates[0] = new GamePadState(PlayerIndex.One);
// etc.
// in your update
foreach (GamePadState s in currentGamePadStates)
{
// update all of this as before...
}
// etc.
Now, you want to test every controller for input, so you'll need to generalise by writing a function that returns a Bool after checking each GamePadState in the arrays for a button press.
Check out the MSDN Game State Management Sample for a well developed implementation. I can't remember if it supports multiple controllers, but the structure is clear and can easily be adapted if not.
Recently, I am studying Symbian development. When I want to use CDirectScreenAccess to draw on the device directly, there occurs the question.
My code is below :
//MySnakeAppView.h
class CMySnakeAppView : public CCoeControl
{
...
private:
void ConstructL(const TRect& aRect);
CDirectScreenAccess* iDSA;
void Restart(RDirectScreenAccess::TTerminationReasons aReason);
void AbortNow(RDirectScreenAccess::TTerminationReasons aReason);
void DrawGraphics();
...
}
//MySnakeAppView.cpp
void CMySnakeAppView::ConstructL(const TRect& aRect)
{
// Create a window for this application view
CreateWindowL();
// Set the windows size
SetRect(aRect);
// Activate the window, which makes it ready to be drawn
ActivateL();
CEikonEnv* env = CEikonEnv::Static();
iDSA = CDirectScreenAccess::NewL(env->WsSession(), *env->ScreenDevice(), Window(), *this);
iDSA->StartL();
DrawGraphics();
}
void CMySnakeAppView::DrawGraphics()
{
CFbsBitGc *gc = iDSA->Gc();
TRgb colorRed = AKN_LAF_COLOR(35);
gc->SetPenColor(colorRed);
gc->DrawRect(TRect(0,0,100,100));
iDSA->ScreenDevice()->Update();
}
void CMySnakeAppView::Restart(RDirectScreenAccess::TTerminationReasons aReason)
{
iDSA->StartL();
DrawGraphics();
}
void CMySnakeAppView::AbortNow(RDirectScreenAccess::TTerminationReasons aReason)
{
iDSA->Cancel();
}
when I build this project, it is wrong with the code
iDSA = CDirectScreenAccess::NewL(env->WsSession(), *env->ScreenDevice(), Window(), *this);
this is a mistake writing that :
'MDirectScreenAccess &'
- illegal implicit conversion from
'CMySnakeAppView' to
but when I do it like this ：
iDSA = CDirectScreenAccess::NewL(env->WsSession(), *env->ScreenDevice(), Window(), (MDirectScreenAccess &)*this);
there is no mistake in building,but still have mistake in the project, I don't know why,I need your help
Your CMySnakeAppView should derive from MDirectScreenAccess - it looks like you're already implementing the right methods, you're just missing the declaration:
class CMySnakeAppView : public CCoeControl, public MDirectScreenAccess
You can't pass *this, because it is not an istance of a MDirectScreenAccess class nor an istance of a class that inherits from it. You can cast it manually, but that is an error. You should construct a class that inherits from MDirectScreenAccess and from there build the iDSA. Look at here:
http://www.developer.nokia.com/Community/Wiki/Anti-tearing_with_CDirectScreenBitmap
I am using gwt and postgres for my project. On the front end i have few widgets whose data i am trying to save on to tables at the back-end when i click on "save project" button(this also takes the name for the created project).
In the asynchronous callback part i am setting more than one table. But it is not sending the data properly. I am getting the following error:
org.postgresql.util.PSQLException: ERROR: insert or update on table "entitytype" violates foreign key constraint "entitytype_pname_fkey"
Detail: Key (pname)=(Project Name) is not present in table "project".
But when i do the select statement on project table i can see that the project name is present.
Here is how the callback part looks like:
oksave.addClickHandler(new ClickHandler(){
#Override
public void onClick(ClickEvent event) {
if(erasync == null)
erasync = GWT.create(EntityRelationService.class);
AsyncCallback<Void> callback = new AsyncCallback<Void>(){
#Override
public void onFailure(Throwable caught) {
}
#Override
public void onSuccess(Void result){ }
};
erasync.setProjects(projectname, callback);
for(int i = 0; i < boundaryPanel.getWidgetCount(); i++){
top = new Integer(boundaryPanel.getWidget(i).getAbsoluteTop()).toString();
left = new Integer(boundaryPanel.getWidget(i).getAbsoluteLeft()).toString();
if(widgetTitle.startsWith("ATTR")){
type = "regular";
erasync.setEntityAttribute(name1, name, type, top, left, projectname, callback);
} else{
erasync.setEntityType(name, top, left, projectname, callback);
}
}
}
Question:
Is it wrong to set more than one in the asynchronous callback where all the other tables are dependent on a particular table?
when i say setProjects in the above code isn't it first completed and then moved on to the next one?
Please any input will be greatly appreciated.
Thank you.
With that foreign key constraint, you must make sure the erasync.setProjects(...) has completed before you insert the rest of the stuff.
I suggest doing the erasync.setEntityAttribute(...) magic in (or from) an onsuccess callback instead of jumping right to it.
You're firing several request in which (guessing from the error message) really should be called in sequence.
Any time you call more than one rpc call; try to think that you should be able to rearrange them in any order (because that's allmost what actually happens because they're asynchronous)... If running them in reverse order does not make sense; you cannot fire them sequentially!
Two ways to fix your problem:
Nesting:
service.callFirst(someData, new AsyncCallback<Void> callback = new AsyncCallback<Void>(){
#Override
public void onFailure(Throwable caught) {/*Handle errors*/}
#Override
public void onSuccess(Void result){
service.callSecond(someOtherData, new AsyncCallback<Void> callback = new AsyncCallback<Void>(){
/* onSuccess and onFailure for second callback here */
});
}
});
Or creating one service call that does both (Recommended):
service.callFirstAndSecond(someData, someOtherData, new AsyncCallback<Void> callback = new AsyncCallback<Void>(){
#Override
public void onFailure(Throwable caught) {/*Handle errors*/}
#Override
public void onSuccess(Void result){
/* Handle success */
}
});
The second option is most likely going to be much less messy, as several nested asynch callbacks quickly grows quite wide and confusing, also you make just one request.
Because of nature of Async, don't assume setProjects(...) method will be called on the server before setEntityAttribute or setEntityType.
Personally, I prefer to have a Project class which contains all necessary info, for example:
public class Project{
private String projectName;
private List attributes = new ArrayList();
.. other properties
// Getter & Setter methods
}
Then send to the server in one round trip:
Project project = new Project();
project.setProjectName(..);
// Set other properties
erasync.saveProjects(project, callback);