sun.misc.Unsafe Sınıfı

Açıklaması şöyle. 

2.2. Unsafe API

The Unsafe API is extremely efficient due to its addressing model. However, as the name suggests, this API is unsafe and has several drawbacks:

- It often allows the Java programs to crash the JVM due to illegal memory usage
- It's a non-standard Java API

constuctor

Örnek

Şöyle yaparız

Field f = Unsafe.class.getDeclaredField("theUnsafe");
f.setAccessible(true);
Unsafe unsafe = (Unsafe) f.get(null);

allocateInstance metodu

Nesne için sadece bellek ayırır ve constructor'ı çağırmaz.

Örnek

Şöyle yaparız

class InitializationOrdering {
  private long a;

  public InitializationOrdering() {
    this.a = 1;
  }

  public long getA() {
    return this.a;
  }
}

InitializationOrdering o3 
  = (InitializationOrdering) unsafe.allocateInstance(InitializationOrdering.class);
 
assertEquals(o3.getA(), 0);

defineAnonymousClass metodu

Java 15 ile Bunun yerine artık Hidden Classes kullanılıyor

getLong metodu

Örnek

Şöyle yaparız

public class Foo {

  private static final long OFFSET_value;
  private static final Unsafe UNSAFE = UnsafeLocator.UNSAFE;

  static {
    try {
      OFFSET_value = getOffset("value");
    } catch (ReflectiveOperationException e) {
      ...
    }
  }

  private static long getOffset(String fieldName) throws NoSuchFieldException {
    Field field = Foo.class.getDeclaredField(fieldName);
    return UnsafeLocator.UNSAFE.objectFieldOffset(field);
  }

  public volatile long value;

  public long unsafe() {
    return UNSAFE.getLong(this, OFFSET_value);
  }
}