How does the garbage collector work in Java

Garbage collection is the process of freeing space on the heap so that new objects can be added.

Objects are created using the new operator, thereby assigning a reference to the object. To finish working with an object, you just need to stop referring to it, for example, by assigning a reference to another object to a variable or the value null; terminate the execution of the method so that its local variables expire naturally. Objects that are not referenced are commonly referred to as garbage, which will be removed.

The Java virtual machine, using the garbage collection mechanism, ensures that any object that has references remains in memory - all objects that are unreachable from the executable code, due to the lack of references to them, are deleted, freeing the memory allocated for them. More specifically, an object is outside the scope of the garbage collection process if it is reachable through a chain of links starting at the GC Root, i.e. a link that directly exists in the executable code.

Memory is freed by the garbage collector at its own discretion. The program can successfully complete its work without exhausting the resources of free memory or not even approaching this limit, and therefore it will not need the "services" of the garbage collector.

Garbage is collected by the system automatically, without user or programmer intervention, but this does not mean that this process does not require attention at all. The need to create and delete a large number of objects significantly affects the performance of applications, and if program performance is an important factor, you should carefully consider decisions related to creating objects - this, in turn, will reduce the amount of garbage to be disposed of.

Read also:


Comments

Post a Comment

Popular posts from this blog

Methods for reading XML in Java

Image
DOM (Document Object Model) - object - reads XML, recreating it in memory in the form of an object structure, while the XML document is represented as a set of tags - nodes. Each node can have an unlimited number of child nodes. Each child can also contain several levels of descendants or none at all. Thus, the result is a kind of tree. Pluses: Easy to program. If there are many objects in XML with cross-references to each other, it is enough to go through the document twice: first time create objects without references and fill in the name-object dictionary, the second time - restore links. If an error occurs in XML, a half-created XML structure remains in memory, which will be automatically destroyed. Suitable for both reading and writing. Minuses: Low speed. Wastes a lot of memory. SAX (Simple API for XML) - event-driven - reads an XML document, responding to emerging events (opening or closing tag, string, attribute) by calling the event handlers provided by the appl...
Read more

XML, well-formed XML and valid XML

Image
XML, the eXtensible Markup Language, is a language with a simple formal syntax, well suited for creating and manipulating documents with programs, and at the same time easy to read and create documents by humans. XML is extensible, it does not fix the markup used in documents, and the developer is free to create markup in accordance with the needs of a particular area, being limited only by the syntax rules of the language. DTD A DTD, Document Type Definition, is a predefined set of rules that defines the relationships between elements and attributes. For example, the DTD for HTML says that the DIV tag must be inside the BODY tag and can appear multiple times, TITLE - in HEAD and only once, and SCRIPT - both there and there as many times as you want. A DTD is usually described directly in the document as a formulation line starting with <!DOCTYPE ... > or in a separate file. Difference between well-formed XML and valid XML Depending on the level of compliance, the document...
Read more

ArrayList and LinkedList in Java, memory usage and speed

Image
How much extra memory is needed when calling ArrayList.add()? If there is enough space in the array to accommodate a new element, then no additional memory is required. Otherwise, a new array is created, 1.5 times larger than the existing one (this is true for JDK above 1.7, in earlier versions the size of the increase is different). How much extra memory is allocated when you call LinkedList.add()? One new instance of the nested Node class is created. How much memory to store one byte primitive in LinkedList? Each LinkedList element stores a link to the previous element, the next element, and a data link. private static class Node<E> { E item; Node<E> next; Node<E> prev; //... } For 32-bit systems, each link is 32 bits (4 bytes). The object (header) of the nested Node class itself takes 8 bytes. 4 + 4 + 4 + 8 = 20 bytes, and since the size of each object in Java is a multiple of 8, so we get 24 bytes. A byte primitive occupies 1 by...
Read more