Using the sun.misc.Unsafe class

The sun.misc.Unsafe class, like other sun classes, is not officially documented or supported. It has been used to circumvent some of Java's built-in memory management safety features. While this can be viewed as a window to greater control and flexibility in our code, it is a terrible programming practice.

The class had a single private constructor, so an instance of the class could not easily be instantiated. So, if we tried to instantiate an instance with myUnsafe = new Unsafe(), a SecurityException would be thrown in most circumstances. This somewhat unreachable class has over 100 methods that permitted operations on arrays, classes, and objects. Here is a brief sampling of those methods:

Arrays	Classes	Objects
arrayBaseOffset	defineAnonymousClass	allocateInstance
arrayIndexScale	defineClass	objectFieldOffset
	ensureClassInitialized
	staticFieldOffset

Here is a secondary grouping of the sun.misc.Unsafe class method for information, memory, and synchronization:

Information	Memory	Synchronization
addressSize	allocateMemory	compareAndSwapInt
pageSize	copyMemory	monitorEnter
	freeMemory	monitorExit
	getAddress	putOrderedEdit
	getInt	tryMonitorEnter
	putInt

The sun.misc.Unsafe class was earmarked for removal in Java 9. There was actually some opposition to this decision in the programming industry. To put their concerns to rest, the class has been depreciated, but will not be completely removed. A special flag can be sent to the JVM to utilize the original API.