![]() ![]() In order to help the Virtual Machine, it is a good idea to remove yourreferences to unneeded objects. Theprocess stops when all objects that it is possible to reach have been marked andthe rest have been discarded. Then,all objects that are referred to by this thread set are marked as current. First, the garbagecollector gets a snapshot of all running threads and all loaded classes. They generally follow the same process, however. The implementation of garbage collection varies between Java VirtualMachines. When it finds them, it destroys them andreclaims the memory. Garbage collection runs as a thread in the background, looking for objectsthat no longer have a usable reference. ![]() When you aredone with an object, the memory is reclaimed for you automatically viaJava's garbage collection facility. It is useful to know that these two different kinds of memory exist in Java.Stack memory is the program's memory, and heap memory resides outside ofthe program.Īs a Java programmer, you do not have to directly address memory allocationand recovery of memory space, which is a common headache for C++ programmers.When you need a new object, Java allocates the required memory. This kind of reassignment makes twostack references to the same object on the heap. The test2 object on the heap still exists, but it cannot be accessed.That's because this reassignment overwrote the old address that test2 was keeping on the stack. After performing the aboveassignment, test2 now holds this address in stack memory: 0x99f775, which refers to the same object as test1. Assume that test1's memory address was 0x33d444 and that test2's address was 0x99f775. What you're actually doing when you write this is assigning the addressof the test1 object to the test2 object. Say you've got two Test objects, and you assign the first tothe second, like this: Test test1 = new Test() Test test2 = new Test() test2 = test1 An object reference on the stack isonly an address that refers to the place in heap memory where that object iskept. Stack memory stores primitive types and the addresses of objects.The object values are stored in heap memory. These are called stack memory andheap memory. There are two kinds of memory used in Java. Thisreference represents the location where the object and its metadata are stored. Anobject reference variable must then hold a reference to those values. The associationbetween each value and the object must be maintained throughout its life. They oftenhold multiple values, each of which must be stored in memory. Objects must be stored differently because they are more complex. The appropriate amount of space is allocated given the data type, and thevariable is stored in memory just as it is. Primitive data types have just one value to store. In this section we will look at how variables are stored in memory in Java.We are examining memory in Java at this point so that you can understand at alower level what happens when you create and manipulate the objects that make upyour programs. Learn More Buy 7.8 Stack and Heap Memory
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