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Java Snake Bug: It happens when change direction quickly

In my Snake code, if the snake is moving LEFT currently, and I then press either UP or DOWN, and then very quickly press RIGHT, the game is over. I knew the reason why it happened, but I don't know how to fix it. Maybe I should announce a new variable for last direction and then compare it with the new direction to decide if the snake should turn to the new direction? I don't know how to fix it. Can somebody help me to solve the problem ? :-)
Here is the relevant code.
//Judge the keyboard input
public void changeDirection(Direction newDirection) {
if (snakeDirection.compatibleWith(newDirection)) {
snakeDirection = newDirection;
}
Direction.java
public enum Direction {
UP(0),
RIGHT(1),
DOWN(2),
LEFT(3);
private final int directionCode;
Direction(int directionCode) {
this.directionCode = directionCode;
}
private int directionCode() {
return directionCode;
}
//
public boolean compatibleWith(Direction direction) {
return (this.directionCode() + direction.directionCode()) % 2 == 1;
}
}
GameController.java
public class GameController implements Runnable, KeyListener {
private final Grid grid;
private final GameView gameView;
boolean running;
public GameController(Grid grid, GameView gameView) {
this.grid = grid;
this.gameView = gameView;
this.running = true;
}
#Override
public void keyPressed(KeyEvent e) {
int keyCode = e.getKeyCode();
switch (keyCode) {
case KeyEvent.VK_UP:
grid.changeDirection(Direction.UP);
break;
case KeyEvent.VK_DOWN:
grid.changeDirection(Direction.DOWN);
break;
case KeyEvent.VK_LEFT:
grid.changeDirection(Direction.LEFT);
break;
case KeyEvent.VK_RIGHT:
grid.changeDirection(Direction.RIGHT);
break;
case KeyEvent.VK_ENTER:
if (running == false) {
grid.init();
running = true;
new Thread(this).start();
}
break;
case KeyEvent.VK_SPACE:
if (running) {
running = false;
} else {
running = true;
new Thread(this).start();
}
break;
default:
break;
}
}
// the Thread
public void run() {
while (running) {
try {
Thread.sleep(200);
} catch (InterruptedException e) {
break;
}
// your code here
if (grid.nextRound()) {
gameView.draw();
} else {
gameView.showGameOverMessage();
break;
}
}
running = false;
}

You really need a new variable. Your snakeDirection is the direction you want to use in the next time step and comparing it with newDirection only helps when it has been used. You need a lastUsedDirection set after a step was done.
Some comments
You can replace directionCode by ordinal().
You should start only a single thread and let it skip the action when running=false. Use the constructor allowing to start it with deamon=true, so that you can terminate the game without it terminating first. Don't let it terminate. You current code risks having multiple threads running when you press SPACE multiple times fast enough.
Be careful with you variable used in multiple threads. As long as one thread only reads the variable and the other one only writes it, it's enough to use volatile. You probably don't even do this and then it can happen that one thread never sees the writes made by another one (this is no theory; this really happens, maybe not in your case).

Just check the x and y positon of the head and the "neck".
What I mean is:
neck
|
| xxxx
| x <--- The snake
HNxx
|
|
head
If the position is the same in one axis, you should not turn.
Here's an actual example (it's C++, but Java has similar syntax, so this shouldn't be a problem).
void Snake::setDirection(char dir) {
switch (direction) {
case Snake::NORTH:
if (dir == Snake::SOUTH) return;
if (body.size() > 1 && body[0]->y == body[1]->y) return;
break;
case Snake::SOUTH:
if (dir == Snake::NORTH) return;
if (body.size() > 1 && body[0]->y == body[1]->y) return;
break;
case Snake::EAST:
if (dir == Snake::WEST) return;
if (body.size() > 1 && body[0]->x == body[1]->x) return;
break;
case Snake::WEST:
if (dir == Snake::EAST) return;
if (body.size() > 1 && body[0]->x == body[1]->x) return;
break;
}
direction = dir;
}
body is a std::vector that holds all the snake segments and direction is a Snake class variable.

Java Switch between cases without every time skipping the remaining cases

I am new to Java, would appreciate some help.
what I am trying to do here is switch between the cases. However what I also need is to not skip the remaining cases in this procedure.
I mean the code below should output:
two
four
three
four
public class X {
public static void main(String[] args) {
String n = "two";
while(true)
{
switch (n)
{
case "zero":
{
System.out.println("zero");
n="one";
}
case "one":
{
System.out.println("one");
n="three";
}
case "two":
{
System.out.println("two");
if (12>3)
{
n="four";
break;
}
}
case "three":
{
System.out.println("three");
}
case "four":
{
System.out.println("four");
return;
}
}
}
}
}
I have used return to end the while loop. Now I do understand that I have used break in case two which will break the current switch and thereby not complete it. But if i don't, I just can't switch between cases in the first place. So, I need a different solution. And working implementation in java should be helpful. Thanks

You can use Queue for this.
Each case is responsible to add the next one to the queue by the order of expected execution.
Queue q = new LinkedList();
q.add("two");
String n = (String)q.poll();
while(n!=null)
{
switch (n)
{
case "zero":
{
System.out.println("zero");
q.add("one");
break;
}
case "one":
{
System.out.println("one");
q.add("three");
q.add("two");
break;
}
case "two":
{
System.out.println("two");
if (12>3)
{
q.add("four");
}
q.add("three");
break;
}
case "three":
{
System.out.println("three");
q.add("four");
break;
}
case "four":
{
System.out.println("four");
break;
}
}
n=(String) q.poll();
}

The problem does not lie within the switch statement. You simply need to distinguish from where you 'came from'.
To do that you need to remember it, e.g. in a local variable:
String lastN;
and in the loop before the switch:
lastN = n;
Now you can do something like:
case "four":
{
System.out.println("four");
if("three".equals(lastN))
{
return;
}
else
{
n = "three";
break;
}
}

Your code is working as it should, if what you need is a fall through
then consider the fact that case zero and one must be executed first...
on the other hand, you don't need to add { } to the case group
case "zero": {
System.out.println("zero");
n = "one";
}

public static void main(String[] args) {
String n = "two";
while(true)
{
switch (n)
{
case "zero":
{
System.out.println("zero");
}
case "one":
{
System.out.println("one");
}
case "two":
{
System.out.println("two");
}
case "four":
{
System.out.println("four");
if(n=="four"){
return;
}
}
case "three":
{
System.out.println("three");
n="four";
}
}
}
}

Reviewing and correcting code style [closed]

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I am new to android developement.
Created calculator application.
Want to improve my code quality.
Will be helpfull for any advice to make the code better and more professional
(overall structure, splitting onto logical units, accordance to code conventions, methods and variables names, comments etc).
Here is my code:
public class OperationsAndFunctions {
static enum OperEnum {
SUM, SUBSTRACT, MULTIPLY, DIVIDE, EQUAL
}
static enum FuncEnum {
RESET, BACKSPACE, SIGN, PERCENT, POINT
}
}
public class LCalculator extends Activity {
private TextView mDisplay;
private boolean mDisplayIsEmpty = true;
private boolean mFirstNumberReceived;
private boolean mNumberEntered;
private boolean mPointEntered;
private double sNum1;
private double sNum2;
private static OperationsAndFunctions.OperEnum sOperation;
private static OperationsAndFunctions.FuncEnum sFunction;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main_layout);
mDisplay = (TextView) findViewById(R.id.tvDisplay);
mDisplay.setText("0");
}
// listening for number buttons pressing
public void num_Clicked(View view) {
Button button = (Button) view;
int number = 0;
// checking button ID
switch (button.getId()) {
case R.id.button1:
number = 1;
break;
case R.id.button2:
number = 2;
break;
case R.id.button3:
number = 3;
break;
case R.id.button4:
number = 4;
break;
case R.id.button5:
number = 5;
break;
case R.id.button6:
number = 6;
break;
case R.id.button7:
number = 7;
break;
case R.id.button8:
number = 8;
break;
case R.id.button9:
number = 9;
break;
case R.id.button0:
if (mDisplay.getText().toString().equals("0")) {
return;
}
number = 0;
break;
}
// setting a new digit onto display if it is empty
if (mDisplayIsEmpty) {
if (!(number == 0)) {
mDisplayIsEmpty = false;
}
mDisplay.setText(Integer.toString(number));
}
// appending digit if display isn't empty
else {
mDisplay.append(Integer.toString(number));
}
mNumberEntered = true;
}
// listenning for operational buttons pressing
public void op_Clicked(View view) {
Button button = (Button) view;
// calculating and printing result
// if a number has been entered before
// (Not entering here if another operation has been pressed before)
if (mNumberEntered) {
// if received first number and saved to sNum1
if (mFirstNumberReceived) {
sNum2 = Double.parseDouble(mDisplay.getText().toString());
printResult(calculateResult(sNum1, sOperation, sNum2));
sNum1 = Double.parseDouble(mDisplay.getText().toString());
}
// if not received first number - receiving it now
else {
sNum1 = Double.parseDouble(mDisplay.getText().toString());
mFirstNumberReceived = true;
}
mNumberEntered = false;
}
// checking operational buttons id
// and assigning appropriate operations enum value
switch (button.getId()) {
case R.id.buttonPlus:
sOperation = OperationsAndFunctions.OperEnum.SUM;
break;
case R.id.buttonMinus:
sOperation = OperationsAndFunctions.OperEnum.SUBSTRACT;
break;
case R.id.buttonMultiply:
sOperation = OperationsAndFunctions.OperEnum.MULTIPLY;
break;
case R.id.buttonDivide:
sOperation = OperationsAndFunctions.OperEnum.DIVIDE;
break;
case R.id.buttonEqual:
sOperation = OperationsAndFunctions.OperEnum.EQUAL;
break;
}
// next digit entered will be a new number
mDisplayIsEmpty = true;
mPointEntered = false;
}
// listening for functional buttons pressing
public void func_Clicked(View view) {
Button button = (Button) view;
// checking operational buttons id
// and assigning appropriate functions enum value
switch (button.getId()) {
case R.id.buttonAc:
sFunction = OperationsAndFunctions.FuncEnum.RESET;
break;
case R.id.buttonC:
sFunction = OperationsAndFunctions.FuncEnum.BACKSPACE;
break;
case R.id.buttonSign:
sFunction = OperationsAndFunctions.FuncEnum.SIGN;
break;
case R.id.buttonPercent:
sFunction = OperationsAndFunctions.FuncEnum.PERCENT;
break;
case R.id.buttonPoint:
sFunction = OperationsAndFunctions.FuncEnum.POINT;
break;
}
// implementing chosen function
implementFunction(sFunction);
}
// implementing function
private void implementFunction(OperationsAndFunctions.FuncEnum function) {
sFunction = function;
switch (function) {
case RESET:
reset();
break;
case BACKSPACE:
printResult(Double.parseDouble(backSpace(mDisplay.getText())
.toString()));
break;
case SIGN:
printResult(readDisplayState() * (-1));
break;
case PERCENT:
printResult(readDisplayState() / 100);
break;
case POINT:
if (!mPointEntered) {
if (!mDisplayIsEmpty) {
mDisplay.append(".");
} else {
mDisplay.setText("0.");
mDisplayIsEmpty = false;
}
mPointEntered = true;
}
break;
}
}
// reseting the calculator
private void reset() {
mDisplay.setText("0");
sNum1 = sNum2 = 0;
mDisplayIsEmpty = true;
mFirstNumberReceived = false;
mNumberEntered = false;
mPointEntered = false;
}
// deleting the last symbol on display
private CharSequence backSpace(CharSequence displayState) {
CharSequence result = displayState;
if (displayState.length() > 1) {
result = displayState.subSequence(0, displayState.length() - 1);
}
else if (displayState.length() == 1) {
result = "0";
}
return result;
}
// calculating the result
private double calculateResult(double num1,
OperationsAndFunctions.OperEnum operation, double num2) {
sNum1 = num1;
sNum2 = num2;
sOperation = operation;
double result = 0;
switch (operation) {
case SUM:
result = num1 + num2;
break;
case SUBSTRACT:
result = num1 - num2;
break;
case MULTIPLY:
result = num1 * num2;
break;
case EQUAL:
mDisplayIsEmpty = true;
mNumberEntered = false;
mFirstNumberReceived = false;
break;
case DIVIDE:
// division by zero
if (num2 == 0) {
showError();
break;
}
result = num1 / num2;
break;
}
return result;
}
// reading current displayNumber
private double readDisplayState() {
return Double.parseDouble(mDisplay.getText().toString());
}
// printing the result
private void printResult(Double result) {
// checking if the result having decimal part
// if not then we print integer value of it without point and zero(s)
if (result % 1 == 0) {
mDisplay.setText(Integer.toString(result.intValue()));
}
else {
mDisplay.setText(Double.toString(result));
}
}
// Error message (in case of division by zero)
private void showError() {
// printing error message
mDisplay.setText("Error");
// and reseting current state
sNum1 = sNum2 = 0;
mDisplayIsEmpty = true;
mFirstNumberReceived = false;
mNumberEntered = false;
mPointEntered = false;
}
}
Thank you very much in advance!

Code style can be either a personal preference, or an organizational guideline. If working for yourself, do what works best for you. Start with some published standard code guidelines (Android Style Guide) and then change things that you don’t like. If you are working within a group, be it an open source project or as part of a project with an employer, there are typically coding standards set forth by them. One bit of advice is even if you are not a fan of the chosen style, abide by it. Having an entire file show as updated just because you reformatted the style to match your preferences is not received well in a team environment. As far as code quality, there are tools (Static analysis) that you can run against your code to give you suggestions of what might be places that could cause problems. (Android Static Analysis)

Switch Statement: Execute Code Once

If I have a switch statement testing the value of integer i, how can I execute the same code once?
For example:
switch(i) {
case 0:
if(j == 2) {
booleanA = true;
booleanB = false;
case 1:
if(j == 4) {
booleanA = true;
booleanB = false;
}
With 5 different cases, instead of me having to type out
booleanA = true;
booleanB = false;
five times, is there a way to say if one of the if statements is true, use this block of code? Is that possible?
Thanks!

You can do it without a switch statement...
int[] requiredJ = {2,4};
if (j == requiredJ[i]) {
booleanA = true;
booleanB = false;
}

I can not understand logic behind your code, but may be this can be done ( Like switch hit in cricket !!! :p).
Assign the values to your booleans, and revert in default case.
booleanA = true;
booleanB = false;
// more code blocks
switch(i) {
case 0:
// Process
break;
case 1:
// Process
break;
default :
booleanA = false;
booleanB = true;
}

How to make a sleep thread in For loop?

I'm working on a card game app and i finished the basic stuff and now i'm trying to make it look professional.
the first thing I want to do is the effect of the distribution of cards,
i want to make a shuffle card effect.
when a card is given to a player, I want at least 500 milliseconds difference to the next card that will be distributed to him.
ideas?
this is a part from my code..
private void SetTheGame() {
SetShuffleSound();
for ( int i = 0; i < Imagename.length;i++) {
Imagename[i] = (ImageView) findViewById(WTF[i]);
CountCards();
Random = getRandom();
SwitchImages SwitchMe = new SwitchImages(myNewArray[Random]);
int first = SwitchMe.ChangeImages();
Imagename[i].setImageResource(myNewArray[Random]);
Imagename[i].setVisibility(View.VISIBLE);
CardsCount valueOfCard = new CardsCount(myNewArray[Random]);
int a = valueOfCard.WhatsMyValue();
String b = valueOfCard.TheFamily();
switch (i) {
case 0:
if (first != 0) {
Imagename[0].setImageResource(first);
}
FirstColumnComputer.add(a);
FirstColumnComputerFAMILY.add(b);
break;
case 1:
if (first != 0) {
Imagename[1].setImageResource(first);
}
SecondColumnComputer.add(a);
SecondColumnComputerFAMILY.add(b);
break;
case 2:
if (first != 0) {
Imagename[2].setImageResource(first);
}
ThirdColumnComputer.add(a);
ThirdColumnComputerFAMILY.add(b);
break;
case 3:
if (first != 0) {
Imagename[3].setImageResource(first);
}
FourColumnComputer.add(a);
FourColumnComputerFAMILY.add(b);
break;
case 4:
if (first != 0) {
Imagename[4].setImageResource(first);
}
FifthColumnComputer.add(a);
FifthColumnComputerFAMILY.add(b);
break;
case 5:
FirstColumnPlayer.add(a);
FirstColumnPlayerFAMILY.add(b);
break;
case 6:
SecondColumnPlayer.add(a);
SecondColumnPlayerFAMILY.add(b);
break;
case 7:
ThirdColumnPlayer.add(a);
ThirdColumnPlayerFAMILY.add(b);
break;
case 8:
FourColumnPlayer.add(a);
FourColumnPlayerFAMILY.add(b);
break;
case 9:
FifthColumnPlayer.add(a);
FifthColumnPlayerFAMILY.add(b);
break;
}
Cards.remove(Random);
// MakeTheCardPause();
}
SentTheLinkedList();
}
MakeTheCardPause() is the problem...
private void MakeTheCardPause() {
Thread Timer = new Thread()
{
public void run()
{
try{
sleep(1000);
}catch(InterruptedException e)
{
e.printStackTrace();
}finally
{
//do something...
}
}
};
Timer.start();
}
thanks!

Many ways you can do this. Thread.sleep(500) is the way was you suggested but it is not what I would recommend. Here are two alternatives
Message Handler
An example
Handler mHandler = new Handler(){
public void handleMessage(Message msg){
super.handleMessage(msg);
switch(msg.what){
case shuffle:
// Do something
break;
case doneShuffle:
//Do something
}
}
};
Asynch Tasks
Here is an example:
private class shuffleCards extends AsyncTask<Card, Integer, Long> {
protected Long doInBackground(Card card) {
//Do something
//shuffle deck
// Escape early if cancel() is called
if (isCancelled()) break;
}
return deck;
}
protected void onProgressUpdate(Integer... progress) {
//Number of shuffled cards??
}
protected void onPostExecute(Long result) {
//Show card
}
}
Remember this is just a background task to display results. Your main thread will be handling the actual card values and handing them over to the Asynch task.
Good Luck

What about this? You need to have the sleep in the working thread, your code above is creating a new thread and telling it to sleep, which has no noticeable effect to the user.
private void SetTheGame() {
SetShuffleSound();
for ( int i = 0; i < Imagename.length;i++) {
Imagename[i] = (ImageView) findViewById(WTF[i]);
CountCards();
Random = getRandom();
SwitchImages SwitchMe = new SwitchImages(myNewArray[Random]);
int first = SwitchMe.ChangeImages();
Imagename[i].setImageResource(myNewArray[Random]);
Imagename[i].setVisibility(View.VISIBLE);
CardsCount valueOfCard = new CardsCount(myNewArray[Random]);
int a = valueOfCard.WhatsMyValue();
String b = valueOfCard.TheFamily();
switch (i) {
case 0:
if (first != 0) {
Imagename[0].setImageResource(first);
}
FirstColumnComputer.add(a);
FirstColumnComputerFAMILY.add(b);
break;
case 1:
if (first != 0) {
Imagename[1].setImageResource(first);
}
SecondColumnComputer.add(a);
SecondColumnComputerFAMILY.add(b);
break;
case 2:
if (first != 0) {
Imagename[2].setImageResource(first);
}
ThirdColumnComputer.add(a);
ThirdColumnComputerFAMILY.add(b);
break;
case 3:
if (first != 0) {
Imagename[3].setImageResource(first);
}
FourColumnComputer.add(a);
FourColumnComputerFAMILY.add(b);
break;
case 4:
if (first != 0) {
Imagename[4].setImageResource(first);
}
FifthColumnComputer.add(a);
FifthColumnComputerFAMILY.add(b);
break;
case 5:
FirstColumnPlayer.add(a);
FirstColumnPlayerFAMILY.add(b);
break;
case 6:
SecondColumnPlayer.add(a);
SecondColumnPlayerFAMILY.add(b);
break;
case 7:
ThirdColumnPlayer.add(a);
ThirdColumnPlayerFAMILY.add(b);
break;
case 8:
FourColumnPlayer.add(a);
FourColumnPlayerFAMILY.add(b);
break;
case 9:
FifthColumnPlayer.add(a);
FifthColumnPlayerFAMILY.add(b);
break;
}
Cards.remove(Random);
long sleepMax = 1000L;
Random r = new Random();
long delay = (long) (r.nextDouble() * range);
Thread.sleep(delay);
}
SentTheLinkedList();
}