Can you force a garbage collecter to run for the specific class?

Answer 1

garbage collection cannot be forced. However, Java provides some methods that allow you to request that the JVM perform garbage collection.

In reality, it is possible only to suggest to the JVM that it perform garbage collection. However, there are no guarantees the JVM will actually remove all of the unused objects from memory (even if garbage collection is run). It is essential that you understand this concept for the exam.

The garbage collection routines that Java provides are members of the Runtime class. The Runtime class is a special class that has a single object (a Singleton) for each main program. The Runtime object provides a mechanism for communicating directly with the virtual machine. To get the Runtime instance, you can use the method Runtime.getRuntime(), which returns the Singleton. Once you have the Singleton you can invoke the garbage collector using the gc() method. Alternatively, you can call the same method on the System class, which has static methods that can do the work of obtaining the Singleton for you. The simplest way to ask for garbage collection (remember-just a request) is

System.gc();

Theoretically, after calling System.gc(), you will have as much free memory as possible. We say theoretically because this routine does not always work that way. First, your JVM may not have implemented this routine; the language specification allows this routine to do nothing at all. Second, another thread might grab lots of memory right after you run the garbage collector.

This is not to say that System.gc() is a useless method-it's much better than nothing. You just can't rely on System.gc() to free up enough memory so that you don't have to worry about running out of memory