ANDROID How to reduce String allocations

I've managed to get my a开发者_开发技巧llocations down to next to nothing using DDMS (great tool), this has drastically reduced my GCs to about 1 or 2 every 3 minutes. Still, I'm not happy because those usually cause a noticeable delay in the game (on some phones) when you interact with it.

Using DDMS, I know what the allocations are, they are Strings being converted from integers used to display game information to the HUD.

I'm basically doing this:

int playerScore = 20929;
String playerScoreText = Integer.toString(playerScore);
canvas.drawText(playerScoreText, xPos, yPos);

This happens once each frame update and the HUD system is modular so I plug things in when I need and this can cause 4 or 5 hud elements to allocate Strings and AbstractStringBuilders in DDMS.

Any way to reduce these further or eliminate all the String allocations and just reuse a String object?

Thanks, Albert Pucciani

Reading your question reminded me of one of Robert Greens articles that I read quite some time ago. It discusses your problem almost identically. http://www.rbgrn.net/content/290-light-racer-20-days-32-33-getting-great-game-performance . Skip down to day 33 and start reading.

Remember the last int score and its string representation. On a new frame check if the score is the same. If the same, then no need to create a new string - just use the old one.

Here's what I've done in the past. This will eliminate string allocations.

I create a char[] of a size that will be at least as large as the maximum number of characters you will need to display on the screen. This means that you should select a maximum high score that is achievable in the game. The way you have it now let's you display a score as high as 2^31-1 which is insanely huge, it's not practical with respect to the game. Keep in mind, this is your game, so it's ok to limit the max score to something more reasonable in the context of the game. Pick a number that will virtually be impossible to achieve. Setting this limit will then set you up to be able to not have to muck around with converting large integers to String objects.

Here's what's required:

First, you need to be able to separate the digits in an integer and convert them to char without creating String objects. Let's say you want to convert the integer of 324 into three separate characters '3','2','4' to be placed in the text char[]. One way you can do this is by taking the value 324 and do a mod 10 to get the lowest digit. So 324%10 = 4. Then divide the value by ten and do another mod 10 to get the next digit. So (324/10)%10 = 2, and (324/100)%10 = 3.

int score = 324;
int firstPlaceInt = score%10; // firstPlace will equal 4
int tensPlaceInt = (score/10)%10; // tensPlace will equal 2
int hundresPlaceInt = (score/100)%10; // hundredsPlace will equal 3

You will have to do the above in a loop, but this expresses the idea of what you're trying to do here.

Next, with these digits you can then convert them to chars by referencing a character map. One way to do this is you can create this character map by making a char[] of size 10 and placing values 0 - 9 in indexes 0 - 9.

char[] charMap = {'0','1','2','3','4','5','6','7','8','9',};

So doing this:

int score = 324;
char firstPlace = charMap[score%10];
char tenslace = charMap[(score/10)%10];
char hundredsPlace = charMap[(score/100)%10];

Will create the chars you need for the 3 digits in score.

Now, after all that, I would limit the highest score to say 99,999 (or whatever makes sense in your game). This means the largest "string" I would need to display is "Score: xx,xxx". This would require a char[] (call it text for this example) of size 13. Initialize the first 7 characters with "Score: ", these will never need to change.

char[] text = new char[13];
text[0] = 'S';
text[1] = 'c';
text[2] = 'o';
text[3] = 'r';
text[4] = 'e';
text[5] = ':';
text[6] = ' ';

The next 6 will vary based on the score. Note, that you may not necessarily fill in all 6 of those remaining characters, therefore you need to create an int (call it scoreCount for this example) which will tell you how many characters in the text char[] are actually relevant to the current score in the game. Let's say I need to display "Score: 324", this only takes 10 chars out of the 13. Write the 3 chars for the score of 324 into char[7] to char[9], and set scoreCount to 10 to indicate the number of valid characters in the char[].

int scoreCount = 7;
text[9] = charMap[score%10]; // This is firstPlace
text[8] = charMap[(score/10)%10]; // This is tensPlace
text[7] = charMap[(score/100)%10]; // This is hundredsPlace
scoreCount = 10;

You will probably have to do the above in a loop, but this should express the general idea of what you're trying to do here.

After that, you can just use drawText (char[] text, int index, int count, float x, float y, Paint paint). index will be 0, and count will be scoreCount which indicates how many characters in text should be drawn. In the example above, it doens't matter what's in text[10] to text[12], it's considered invalid. You can continue to update text[] using the character map, and this should not create any objects.

I hope this helps. The code above isn't very robust, but I wrote it out as more of an expression of the ideas I'm trying to convey. You will have to create your own loops and manage the data properly within your code, but this sums up the mechanics of what needs to happen to avoid the use of Strings/StringBuilder/StringBuffer/etc.