Over the past week, some users have encountered Java cleanup error code. There are a number of factors that can cause this problem. We’ll cover them below.
The Java runtime has a garbage collector that periodically reclaims unused space used by objects. The garbage collector does its job automatically. In some situations, you may need to explicitly request garbage collection by calling the gc method on the System.
Design a class to clean up elements correctly
Three months ago, I began my mini-article series on object design by discussing design principles for getting good initialization early in an object’s life. In this article on design techniques, I will focus on design principles that you can use to ensure proper cleaning at the end of a facility’s life.
Every object in a Java program uses finite computational resources. The most obvious is that all objects use memory to store their images on the heap. (This also applies to objects that do not declare nebelt copies. Each object image must contain some sort of pointer to the class data, and may also contain other implementation-dependent information.) However, objects can use other finite resources besides memory. For example, some objects may use resources such as file descriptors, graphics contexts, sockets, etc. When designing an object, you need to make sure that it eventually releases all the limited resources it uses so that the system does not run out of resources.
Since Java is a garbage collection language, it is easy to free the memory associated with an object. All you have to do is drop all references to the object. Since you don’t need to worry about explicitly releasing an object, as in languages such as C or C , you don’t need to worry about memory corruption due to accidentally freeing an object. the same object twice. However, you need to make sure that you have actually released all references to the object. Otherwise, it can cause a memory leak, just like a memory leak in a C program when you run You explicitly release objects. However, as long as you deallocate all references to an object, you don’t need to worry about explicitly “freeing” that memory.
Likewise, you don’t have to worry about explicitly releasing all components that are referenced by the instance variables of an object you no longer need. When all object references that are not required are released, all object references contained in the instance variables of that object become invalid. If the now invalid references were the only remaining references to these constituent objects, the constituent objects would also be available for garbage collection. Child’s play, isn’t it?
Garbage Collection Rules
Although garbage collection makes memory management much easier in Java than in C or C , you cannot completely forget about memory when programming in Java. To know when you might need to think about memory management in Java, you need to know a little about how garbage collection is handled in the Java specs.
No garbage collection required
The first thing you need to know is what toAs much as you search for the Java Virtual Machine (JVM) specification, you cannot find the game instructions for each JVM to have a garbage collector. The JVM specification gives virtual machine developers a lot of leeway in deciding how their implementations handle memory, including the need for garbage collection. As a result, some JVMs (such as a JVM with a simple smart card) may require that the programs executed in each session “fit” in available memory.
Of course, virtual storage can always run out of memory. The JVM specification does not specify the amount of memory available to the JVM. It simply means that the JVM should throw an
OutOfMemoryError if there is not enough memory available.
Most JVMs use a garbage collector to enable Java applications to run without running out of memory. The garbage collector frees memory used by unreferenced objects on the heap so that the memory can be reused by new objects, and usually parses the heap while the program is running.
Alg No garbage collection rhythm defined
Another command that you will not find in the JVM specification is that all JVMs that use garbage collection must use the XXX algorithm. The developers of each JVM can decide how garbage collection works in their implementations. Garbage collection is one area where JVM vendors can strive to implement better than competitors. This is important to you as a Java programmer for the following reason:
Since you usually don’t know how garbage collection is performed in the JVM, you don’t know when a particular object is garbage collected.
So what? You might ask, “The reason you might be interested in seeing the deleted item is because of finalizers.” (A finalizer is defined as a standard Java instance method named
finalize () that returns void and takes no arguments.) The Java specification promises the following for finalizers:
Before freeing memory used by an object using a finalizer, the garbage collector calls the object’s finalizer.
Since you don’t know when objects areThey are collected by spam, but you know that finalizable objects are completed when collected by spam, you can draw the following important conclusion:
You don’t know when the questions will be completed.
You should capture this important fact in your brain and leave it forever to inform your Java object projects.
Central golden rule for finalizers:
Do not design your Java programs in such a way that their accuracy depends on timely completion.
In other words, don’t write programs that break if certain objects don’t complete at certain points in the program’s life. If you write a program like this, it might work with some JVM implementations, but not others.
Do not rely on finalizers to free resources other than memory.
An example of an object that violates this rule is an object that opens a file in its constructor and closes the file in its
finalize () method. While this design looks neat, tidy and symmetrical, it can create an insidious flaw. approx. A Java program usually has a limited number of file descriptors. If all of these descriptors are used, the program will no longer be able to open files.
A Java program using such an object (opening a file in its constructor and closing it in its finalizer) may work fine with some JVM implementations. In such implementations, finalization will occur frequently enough that a sufficient number of file descriptors will always be available. However, the same program might crash on another Java virtual machine that is not garbage collected enough to cause the program to run out of file descriptors. Or, more insidiously, the program can work on all JVM implementations now, but will fail after a few years (and release cycles) in a business critical situation.
Other basic rules for finalizer
Two other decisions that are left to the discretion of the JVM developers are the choice of the thread (or threads) in which the finalizers will run, and the order in which the finalizators. Finalizers can be run in any order – sequentially from one thread or from multiple threads at the same time. If your program depends on finalizers working in a specific order, or on a specific thread for precision, it may work for some JVM implementations, but not for others.
Also note that Java considers the object to be completed, regardless of whether the
finalize () method returns normally or exits abruptly, throwing an exception. Garbage collectors ignore all exceptions thrown by finalizers and do not notify them in any way