Should I save memory by using byte, short and float?
Our teacher tells us always to use int and double. But what if I don't need such precision or large values?
Shouldn't I use byte, short and float instead?
You don't save any memory if you use floats instead of doubles in a method. These variables only exist on the stack when the method is executing. Also remember that Java may do type conversions from float to double in expressions. This may make your code slower.
If you have a class with large quantities of doubles, for example an array of 100000 doubles, then you may consider using floats, because the memory saving is substantial. If you access the array from outside the class via double methods you can easily do this change local to the class late in the development process.
I'd say generally it's better to do as your teacher says and standardize on doubles and integers. If you write your program well you can always optimize later if you have to.
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when do i should really use byte and short anyway?
let's say i'm writing a MIDlet and i really really want to save up some memory at run time, would it be helpful if i will use short and byte if i dont need large numbers? let's say i only need a maximum representation of 500?
i know int is commonly used, but is it worth the change?I don't know about the Micro Editon VM, but the Java Standard Edition run-time VM has no special instructions for operating using byte primitives as opposed to, say, integer or short primitives, and byte primitives in the VM are stored as ints, I believe. So, chances are your optimizations of these primitives aren't going to save you that much in terms of speed or memory. However, again, my previous comments only apply to the Standard Edition VM [feel free to correct them if I am wrong, as I am not sure if these restrictions have changed since Java v1.3 or not].
Plus, if your value is going to be a maximum of 500, you need a short because the signed byte primitive will only be valid across the -128 to 127 range.
-Dok -
Use always int or short and byte if int is not needed?
If I have a variable for percentage and if I don't want to use double or float, what type should the variable be? byte? short? int? long?
Is there a rule? What is a good style?The problem is with casting and that it seems that
Java programmers just use int and double no matter if
they really need such great values and precision.
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Wasn't being condescending, this is a new thead that continues one he already started asking if he could get iWeb on the iPad. Two people explained to him that iWeb was being discontinued (along with MobileMe) and suggested Rapidweaver and two other apps as replacements. It was also explained to him that there were no web creation apps on the iPad because you need to run a local web server, such as Apache, on your computer in order to use them. This is why they work on the Mac because it does have such a server. The iPad does not have one and cannot run one. And I suggested using HTML code if he wanted to develop on his iPad.
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Message was edited by: deggie
Message was edited by: deggie -
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Register() and register(byte[], short, byte)
According to JavaCard 2.2.1 API:
register()
-This method is used by the applet to register this applet instance with the Java Card runtime environment and to assign the Java Card platform name of the applet as its instance AID bytes.
register(byte[], short, byte)
-This method is used by the applet to register this applet instance with the Java Card runtime environment and assign the specified AID bytes as its instance AID bytes.
1. As far as I know, the later is used for assigning specific instance AID. But if the register() is used, what is the instance AID?
2. If I have registered only one instance with JCRE, should I select it by its applet AID or instance AID? Why is it so?
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my question :
if I want to storage ID and password data to smart card memory .. where I must to place these data, so I can update that data on other time..
do you have some code that similiar with my applet ?
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Is it really worth to use primitive datatypes like byte and short over int, when arithmetic is used? I've read that byte and short are converted to int prior to arithmetic and it just seems cumbersome when some of your bytes/shorts mingle with ints. When do people actually use these datatypes other than memory critical apps?
thanksThe reason I ask is because I have some values that fit within a byte and so I thought it best to use the smallest appropriate data type, but at times working with byte has proven to be a pain so I was thinking of just moving most of my bytes to ints. I was more just concerned with the impact on memory.
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Problem using byte indexed pixel format in setPixels method of PixelWriter
I try to construct a byte array and set it to a WritableImage using PixelWriter's setPixels method.
If I use an RGB pixel format, it works. If I use a byte-indexed pixel format, I get an NPE.
The stride etc should be fine if I'm not mistaken.
java.lang.NullPointerException
at com.sun.javafx.image.impl.BaseByteToByteConverter.<init>(BaseByteToByteConverter.java:45)
at com.sun.javafx.image.impl.General$ByteToByteGeneralConverter.<init>(General.java:69)
at com.sun.javafx.image.impl.General.create(General.java:44)
at com.sun.javafx.image.PixelUtils.getB2BConverter(PixelUtils.java:223)
at com.sun.prism.Image$ByteAccess.setPixels(Image.java:770)
at com.sun.prism.Image.setPixels(Image.java:606)
at javafx.scene.image.WritableImage$2.setPixels(WritableImage.java:199)
Short, self-contained example here:
import java.nio.ByteBuffer;
import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.image.ImageView;
import javafx.scene.image.PixelFormat;
import javafx.scene.image.WritableImage;
import javafx.scene.layout.BorderPane;
import javafx.stage.Stage;
public class IndexedColorTestApp extends Application {
public static void main(String[] args) {
launch(args);
@Override
public void start(Stage primaryStage) {
BorderPane borderPane = new BorderPane();
Scene scene = new Scene(borderPane, 600, 1100);
primaryStage.setScene(scene);
ImageView imageView = new ImageView();
borderPane.setCenter(imageView);
primaryStage.show();
int imageWidth = 200;
int imageHeight = 200;
WritableImage writableImage = new WritableImage(imageWidth, imageHeight);
// this works
byte[] rgbBytePixels = new byte[imageWidth * imageHeight * 3];
PixelFormat<ByteBuffer> byteRgbFormat = PixelFormat.getByteRgbInstance();
writableImage.getPixelWriter().setPixels(0, 0, imageWidth, imageHeight,
byteRgbFormat, rgbBytePixels, 0, imageWidth * 3);
imageView.setImage(writableImage);
// this throws an NPE in setPixels()
byte[] indexedBytePixels = new byte[imageWidth * imageHeight];
int[] colorPalette = new int[256];
PixelFormat<ByteBuffer> byteIndexedFormat = PixelFormat.createByteIndexedInstance(colorPalette);
writableImage.getPixelWriter().setPixels(0, 0, imageWidth, imageHeight,
byteIndexedFormat, indexedBytePixels, 0, imageWidth);
imageView.setImage(writableImage);
}If there's no solution, maybe someone knows a workaround? We chose to use indexed format because of data size / performance reasons.
Edited by: Andipa on 01.03.2013 10:52You have found a platform bug, file it against the Runtime project at => http://javafx-jira.kenai.com with your sample code and a link back to this forum question.
Byte indexed pixel formats seem like a feature which was never completely (or perhaps even hardly at all) implemented to me.
The PixelFormat type your failed case is using is (PixelFormat.Type.BYTE_INDEXED):
PixelFormat<ByteBuffer> byteIndexedFormat = PixelFormat.createByteIndexedInstance(colorPalette);
System.out.println(byteIndexedFormat.getType());These are the valid PixelFormat types =>
http://docs.oracle.com/javafx/2/api/javafx/scene/image/PixelFormat.Type.html
BYTE_BGRA
The pixels are stored in adjacent bytes with the non-premultiplied components stored in order of increasing index: blue, green, red, alpha.
BYTE_BGRA_PRE
The pixels are stored in adjacent bytes with the premultiplied components stored in order of increasing index: blue, green, red, alpha.
BYTE_INDEXED
The pixel colors are referenced by byte indices stored in the pixel array, with the byte interpreted as an unsigned index into a list of colors provided by the PixelFormat object.
BYTE_RGB
The opaque pixels are stored in adjacent bytes with the color components stored in order of increasing index: red, green, blue.
INT_ARGB
The pixels are stored in 32-bit integers with the non-premultiplied components stored in order, from MSb to LSb: alpha, red, green, blue.
INT_ARGB_PRE
The pixels are stored in 32-bit integers with the premultiplied components stored in order, from MSb to LSb: alpha, red, green, blue.As the native pixel format for a WritableImage is not the same as the pixel format you are using, the JavaFX platform needs to do a conversion by reading the pixels in one format and writing them in another format. To do this it must be able to determine a PixelGetter for your PixelFormat (the PixelGetter is an internal thing, not public API).
And here is the source the determines the PixelGetter for a given PixelFormat type:
http://hg.openjdk.java.net/openjfx/8/master/rt/file/06afa65a1aa3/javafx-ui-common/src/com/sun/javafx/image/PixelUtils.java
119 public static <T extends Buffer> PixelGetter<T> getGetter(PixelFormat<T> pf) {
120 switch (pf.getType()) {
121 case BYTE_BGRA:
122 return (PixelGetter<T>) ByteBgra.getter;
123 case BYTE_BGRA_PRE:
124 return (PixelGetter<T>) ByteBgraPre.getter;
125 case INT_ARGB:
126 return (PixelGetter<T>) IntArgb.getter;
127 case INT_ARGB_PRE:
128 return (PixelGetter<T>) IntArgbPre.getter;
129 case BYTE_RGB:
130 return (PixelGetter<T>) ByteRgb.getter;
131 }
132 return null;
133 }As you can see, the BYTE_INDEXED format is not handled and null is returned instead . . . this is the source of your NullPointerException. -
Content of message deleted to save memory, where to set?
Hi,
When trying to display "Message Content" in the Message Monitoring in the Runtie Workbench do I get the message
"Content of message deleted to save memory"
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StephanHi all,
I'm just adding this because I think the result of the answers is maybe still not what would be expected by the average XI user :
( all explanations are done for a sync SOAP receiver example )
-Changing settings in the XI integration engine configuration only affects the SXMB_MONI view ( not the adapter(s) view via RWB )
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In my experience, the results regarding this are mixed for several adapters : for the RNIF adapter you see the raw messages but apparently for soap not...
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Hope this helps future users
regards
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Nasty memory leak using sockets inside threads
In short, any time I create or use a socket inside a worker thread, that Thread object instance will never be garbage collected. The socket does not need to be connected or bound, it doesn't matter whether I close the socket or not, and it doesn't matter whether I create the Socket object inside the thread or not. As I said, it's nasty.
I initially encountered this memory leak using httpclient (which creates a worker thread for every connect() call), but it is very easy to reproduce with a small amount of stand-alone code. I'm running this test on Windows, and I encounter this memory leak using the latest 1.5 and 1.6 JDK's. I'm using the NetBeans 5.5 profiler to verify which objects are not being freed.
Here's how to reproduce it with an unbound socket created inside a worker thread:
public class Test {
public static class TestRun extends Thread {
public void run() {
new Socket();
public static void main(String[] strArgs) throws Exception {
for(;;) {
(new TestRun()).start();
Thread.sleep(10);
}Here's how to reproduce it with a socket created outside the thread and used inside the worker thread:
public class Test {
public static class TestRun extends Thread {
Socket s;
public TestRun(Socket s) { this.s = s; }
public void run() {
try {
s.bind(new InetSocketAddress(0));
s.close();
} catch(Exception e) {}
public static void main(String[] strArgs) throws Exception {
for(;;) {
(new TestRun(new Socket())).start();
Thread.sleep(10);
}Here's how to reproduce it implementing Runnable instead of extending Thread:
public class Test {
public static class TestRun implements Runnable {
public void run() {
Socket s = new Socket();
try { s.close(); } catch(Exception e) {}
public static void main(String[] strArgs) throws Exception {
for(;;) {
(new Thread(new TestRun())).start();
Thread.sleep(10);
}I've played with this a lot, and no matter what I do the Thread instance leaks if I create/use a socket inside it. The Socket instance gets cleaned up properly, as well as the TestRun instance when it's implementing Runnable, but the Thread instance never gets cleaned up. I can't see anything that would be holding a reference to it, so I can only imagine it's a problem with the JVM.
Please let me know if you can help me out with this,
SeanFind out what is being leaked. In the sample programs, add something like this:
static int loop_count;
while (true) {
if (++count >= 1000) {
System.gc();
Thread.sleep(500); // In case gc is async
System.gc();
Thread.sleep(500);
System.exit(0);
}Then run with java -Xrunhprof:heap=sites YourProgram
At program exit you get the file java.hprof.txt which contains something like this towards the end of the file:
percent live alloc'ed stack class
rank self accum bytes objs bytes objs trace name
1 0.47% 0.47% 736 5 736 5 300036 char[]
2 0.39% 0.87% 616 3 616 3 300000 java.lang.Thread
3 0.30% 1.17% 472 2 472 2 300011 java.lang.ThreadLocal$ThreadLocalMap$Entry[]
4 0.27% 1.43% 416 2 416 2 300225 java.net.InetAddress$Cache$Type[]See, only three live Thread objects (the JVM allocates a few threads internally, plus there is the thread running main()). No leak there. Your application probably has some type of object that it's retaining. Look at "live bytes" and "live objs" to see where your memory is going. The "stack trace" column refers to the "TRACE nnnnn"'s earlier in the file, look at those to see where the leaked objects are allocated.
Other quickies to track allocation:
Print stats at program exit:
java -Xaprof YourProgram
If your JDK comes with the demo "heapViewer.dll" (or
heapViewer.so or whatever dynamic libraries are called on your system):
java -agentpath:"c:\Program Files\Java\jdk1.6.0\demo\jvmti\heapViewer\lib\heapViewer.dll" YourProgram
Will print out statistics at program exit or when you hit Control-\ (Unix) or Control-Break (Windows).
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