Java Language Tutorial => Uses of Unsafe

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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	`getVolatile`, `putVolatile`, `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`

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Java Language sun.misc.Unsafe Uses of Unsafe

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