Uses of Unsafe

Some uses of unsafe is s follows:

Use | API | —— | —— | Off heap / direct memory allocation, reallocation and deallocation | allocateMemory(bytes), reallocateMemory(address, bytes) and freeMemory(address) | Memory fences | loadFence(), storeFence(), fullFence() | Parking current thread | park(isAbsolute, time), unpark(thread) | Direct field and or memory access | get* and put* family of methods | Throwing unchecked exceptions | throwException(e) | CAS and Atomic Operations | compareAndSwap* family of methods | Setting out memory | setMemory | Volatile or concurrent operations | get*Volatile, put*Volatile, putOrdered* |

The get and put family of methods are relative to a given object. If the object is null then it is treated as an absolute address.

// Putting a value to a field
protected static long fieldOffset = UNSAFE.objectFieldOffset(getClass().getField("theField"));
UNSAFE.putLong(this, fieldOffset , newValue);

// Puting an absolute value
 UNSAFE.putLong(null, address, newValue);
 UNSAFE.putLong(address, newValue);

Some methods are only defined for int and longs. You can use these methods on floats and doubles using floatToRawIntBits, intBitsToFloat,doubleToRawLongBits,longBitsToDouble`