Download Java Games To Memory Card

I'm using an HTC Desire 610 for Android development. I followed the examples in other answers to the same question, but all my file saves end up on internal device storage, and not the SD card. The phone definitely recognizes the SD card, and from within the phone I can transfer files to the SD card.

I tried hard-coding the file path to the SD card, and I also tried running the app while not plugged into the computer - all to no avail. It is extremely important that my app be able to save these files directly to the SD card. Any ideas?

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I am working on a Java Card applet (for Java Card 2.2.1) which requires some temporary objects for processing APDU commands. I have questions about correct memory management.I have spent plenty of time on researching on the issues, but no where I have found any clarification or good sample codes on some java card APIs. I have 2 major questions:

How can I create an array of transient objects (I mean custom objects in RAM not in EEPROM). I have read about makeTransientObjectArray but it returns only array of Object type. I know how to create for example, transient byte array using makeTransientByteArray, but my problem is about transient array of object instances. Or may be any way in java language to cast byte array to instances without serialization?

I need this transient array of objects only during process of incoming APDU command and not need to keep the memory allocated for me. Where is the best place to allocate this transient memory (inside install, select, process, ... functions)?

As I have already read from documentations, any object instance is stored in EEPROM. Assume that I know max number of objects I will need in my process algorithm (say 100). I generate 100 instances of MyClass inside install method. Each instance of MyClass contains 3 fields: field1 a short, field2 a byte, and field3 a short type. All these 100 instances will be filled by input of APDU command. If for each command, I fill objects on EEPROM, its not a good practice, because they are temporary data. Also EEPROM has a max wiriting cycles. An approach may be that for each instance, I allocate 5 bytes for each object using makeTransientByteArray and makeTransientShortArray. But as I have read from documentations, It allocates memory by clusters (of 32 bytes - not sure for size) which is not effective. So what I have to do in this scenario?

I mean what to do for transient memory. If allocate transient memory inside install function, it will not be available for other applets. If the applet is the only one applet on the Card, it is a good practice to allocate all transient memory in install function. I want to know a general effective method for all conditions (single applet device or multi-applet device). Also I am not sure, if transient memory allocated inside install, will be available inside process function whenever the card is inserted in the card reader.

Java is a relatively high level language where objects are always stored in one particular piece of memory. Now they have changed that type of memory to persistent memory for Java Card. However, it would require a complete redesign of the language to allow objects to be constructed in one type of memory or another. Nowadays the JCF could of course consider using annotations for that - it would still be extremely tricky but possibly doable.

One good strategy to use is to create a cache of objects that contain transient memory or reference existing memory such as memory within the APDU buffer. The objects would be created during installation or personalization. These objects then can be retrieved when necessary, used and returned to the cache. To give you an idea, take a look at Java's ByteBuffer.wrap() method that allows you to perform buffer operations on part of an existing array. Now consider a reuseable object of that type.

JavaCard specification provides a method makeTransientObjectArray(short, byte) to make an array of transient objects. This will allocate a memory on RAM and then you can store the reference of your objects in this memory.

However, you cannot still completly acheive what you are trying to, because the objects instantiated in YourClass might be still be consuming memory from non transient memory (EEPROM) or transient (RAM) depending upon their allocation in the constructor of YourClass. It is only the reference of the objects of YourClass is what you are storing in a transient space (aob).

The x variable does not really exist in byte code. There are operations on a location in the Java stack that represents x (be it Java byte code or the code after conversion by the Java Card converter). Now the Java stack is a virtual stack. This stack is implemented on a CPU that has registers and a non-virtual stack. In general, if there are enough registers available, then the variable x is simply put in a register until it is out of scope. The register may of course be reused. The CPU stack itself is a LIFO (last in first out) queue in transient memory (RAM). The stack continuously grows and shrinks during the execution of the byte code that makes up your Applet. Like registers, the stack memory is reused over and over again. All the local variables (those defined inside code blocks as well as method arguments) are treated this way.

If you put your variable in a transient array then you are putting the variable on a RAM based heap. The Java Card RAM heap will never go out of scope. That means that if you update the value that the change needs to be written to transient memory. That is of course slower than a localized update of a CPU register, as you found by experimentation. Usually the memory in the transient memory is never freed. That said, you can of course reuse the memory for other purposes, as long as you have a reference to the array. Note that the references themselves (the index in index[0]) may be either in persistent memory (EEPROM or flash) or transient memory.

It's unclear what you mean with "normal variable". If this is something that has been created with new or if it is a field in an object instance then it persists in the heap in persistent memory (EEPROM or flash). EEPROM and flash have limited amount of write cycles and writing to EEPROM or flash is much much slower than writing to RAM.

Java Card contains two kinds of transient memory: CLEAR_ON_RESET and CLEAR_ON_DESELECT. The difference between the two is that the CLEAR_ON_RESET allows memory to be shared between Applet instances while the CLEAR_ON_DESELECT allows memory to be reused by different Applets.

Java Card classic doesn't contain a garbage collector that runs during Applet execution, you can usually only request garbage collection during startup using JCSystem.requestObjectDeletion() which will clean up the memory that is not referenced anymore, both on the heap in transient memory as well as in persistent memory. Cleaning up the memory means scanning all the memory, marking all the unreferenced blocks and then compacting the memory. This is similar to defragmenting a hard disk; it can take a uncomfortably long time.

The card's OS and Java Card APIs and some factory proprietary packages stored here. The contents of this memory is fixed and you can't modify it. Writing in this memory happens only once in the chip production and the process is named Masking.

Now, your external memory will most likely have a different name than mine. Best way to know what it is is to open it up on your file navigation, and then click the bar at the top and copy that letter/number/name into the file directory on the launcher.

I'm thinking of installing Minecraft java edition onto my laptop, but my storage is fucked up enough already, and Minecraft is crudding on it more. I have an SD card with plenty of storage I COULD install it on, but I'm not sure if that would work? Would it?

Java Card is a software technology that allows Java-based applications (applets) to be run securely on smart cards and more generally on similar secure small memory footprint devices[1] which are called "secure elements" (SE). Today, a secure element is not limited to its smart cards and other removable cryptographic tokens form factors; embedded SEs soldered onto a device board and new security designs embedded into general purpose chips are also widely used. Java Card addresses this hardware fragmentation and specificities while retaining code portability brought forward by Java.

Java Card is the tiniest of Java platforms targeted for embedded devices. Java Card gives the user the ability to program the devices and make them application specific. It is widely used in different markets: wireless telecommunications within SIM cards and embedded SIM, payment within banking cards[2] and NFC mobile payment and for identity cards, healthcare cards, and passports. Several IoT products like gateways are also using Java Card based products to secure communications with a cloud service for instance.

The first Java Card was introduced in 1996 by Schlumberger's card division which later merged with Gemplus to form Gemalto. Java Card products are based on the specifications by Sun Microsystems (later a subsidiary of Oracle Corporation). Many Java card products also rely on the GlobalPlatform specifications for the secure management of applications on the card (download, installation, personalization, deletion).

Java Card aims at defining a standard smart card computing environment allowing the same Java Card applet to run on different smart cards, much like a Java applet runs on different computers. As in Java, this is accomplished using the combination of a virtual machine (the Java Card Virtual Machine), and a well-defined runtime library, which largely abstracts the applet from differences between smart cards. Portability remains mitigated by issues of memory size, performance, and runtime support (e.g. for communication protocols or cryptographic algorithms). 2351a5e196