In Java, memory management refers to allocating and freeing space for objects. Java maintains memory automatically. Java’s “garbage collector” is an autonomous memory management mechanism. As a result, we don’t need to include memory management logic in our software.
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Java Memory Management is divided into two major part :
- JVM Memory Structure
- Working of the Garbage Collector
JVM Memory Structure
- A region named Method Area exists in the heap memory, which is shared by all threads. When the JVM boots up, it produces.
- The superclass name, the interface name, and the constructors are all stored there.
- It contains class-specific elements such as fields, constant pools, method local data, method codes, Constructor codes, and so on, which are used to initialize objects and interfaces.
- If the memory in the method area cannot be made accessible to satisfy an allocation request, the Java Virtual Machine throws an OutOfMemoryError.
- It could be fixed or variable in size. It may not have an ongoing memory.
- Objects created while a Java application is executing are stored in heap memory.
- Stack memory stores the reference to freshly generated items. Heap memory allocation comes after dynamic memory allocation (memory is allocated during execution or runtime).
- Heap memory is bigger in size than stack memory.
- Any superfluous items in heap memory are immediately removed by the garbage collector.
- Memory on the heap does not have to be contiguous.
- JVM allows the user to initialize or adjust the heap size as needed.
- When a calculation requires more heap than the automatic storage management method can offer, the Java Virtual Machine throws an OutOfMemoryError.
- When a new keyword is used, an object is placed on the heap, but it is a reference to an item that already exists on the stack.
- The stack area is created when a thread starts. It could be constant or variable in size.
- Each thread has its own stack memory allocation. There are data and unfinished outcomes kept there.
- It contains heap object pointers.
- Furthermore, rather than a reference to a heap item, it stores the value directly.
- The term “scope” relates to the visibility of variables kept in the stack.
- Stack memory does not have to be continuous.
Native Method Stack
The Java programming language does not provide native method stacks, sometimes known as C stacks. When a thread is created, it is given some memory. Furthermore, it can be either fixed or dynamic.
Program Counter (PC) Registers
Every thread is associated with a Program Counter (PC) register. The PC register stores a native pointer or the return address. It also contains the location of the JVM instructions that are currently being executed.
Working of Garbage Collector
JVM is in charge of the garbage collector. JVM decides when to perform garbage collection. We can also instruct the JVM to activate the garbage collector. However, there is no guarantee that the JVM will follow the rules. When the JVM detects that memory is running low, the garbage collector kicks in. The JVM frequently reacts fast to garbage collector requests from Java programs. It does not ensure that the recommendations will be implemented.
Garbage collection is a costly process because it halts all other processes or threads. Although the client finds this scenario unbearable, it is fixable by employing a variety of garbage collector-based approaches. This algorithm application process, sometimes referred to as garbage collector tuning, is critical for improving program speed.
A different option is provided by generational garbage collectors, which add an age field to objects that are allocated memory. The time required to collect rubbish increases as more items are generated and added to the garbage list. The objects are classified into groups and assigned an age based on the number of clock cycles they have undergone. The waste collection effort is distributed in this manner.
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