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(), 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.