Puede obtener el índice del objeto con Inseguro. Dependiendo de cómo la JVM está utilizando la memoria (direcciones de 32 bits, índice de 32 bits, índice de 32 bits con desplazamiento, dirección de 64 bits) puede afectar la utilidad del índice del objeto.
Aquí hay un programa que supone que tiene un índice de 32 bits en una JVM de 64 bits.
import sun.misc.Unsafe;
import java.lang.reflect.Field;
import java.util.Arrays;
import java.util.Collections;
public class OrderOfObjectsAfterGCMain {
static final Unsafe unsafe = getUnsafe();
static final boolean is64bit = true; // auto detect if possible.
public static void main(String... args) {
Double[] ascending = new Double[16];
for(int i=0;i<ascending.length;i++)
ascending[i] = (double) i;
Double[] descending = new Double[16];
for(int i=descending.length-1; i>=0; i--)
descending[i] = (double) i;
Double[] shuffled = new Double[16];
for(int i=0;i<shuffled.length;i++)
shuffled[i] = (double) i;
Collections.shuffle(Arrays.asList(shuffled));
System.out.println("Before GC");
printAddresses("ascending", ascending);
printAddresses("descending", descending);
printAddresses("shuffled", shuffled);
System.gc();
System.out.println("\nAfter GC");
printAddresses("ascending", ascending);
printAddresses("descending", descending);
printAddresses("shuffled", shuffled);
System.gc();
System.out.println("\nAfter GC 2");
printAddresses("ascending", ascending);
printAddresses("descending", descending);
printAddresses("shuffled", shuffled);
}
public static void printAddresses(String label, Object... objects) {
System.out.print(label + ": 0x");
long last = 0;
int offset = unsafe.arrayBaseOffset(objects.getClass());
int scale = unsafe.arrayIndexScale(objects.getClass());
switch (scale) {
case 4:
long factor = is64bit ? 8 : 1;
final long i1 = (unsafe.getInt(objects, offset) & 0xFFFFFFFFL) * factor;
System.out.print(Long.toHexString(i1));
last = i1;
for (int i = 1; i < objects.length; i++) {
final long i2 = (unsafe.getInt(objects, offset + i * 4) & 0xFFFFFFFFL) * factor;
if (i2 > last)
System.out.print(", +" + Long.toHexString(i2 - last));
else
System.out.print(", -" + Long.toHexString(last - i2));
last = i2;
}
break;
case 8:
throw new AssertionError("Not supported");
}
System.out.println();
}
private static Unsafe getUnsafe() {
try {
Field theUnsafe = Unsafe.class.getDeclaredField("theUnsafe");
theUnsafe.setAccessible(true);
return (Unsafe) theUnsafe.get(null);
} catch (Exception e) {
throw new AssertionError(e);
}
}
}
se ejecuta en Java 6 Update 26 (de 64 bits con comprimido vaya) y Java 7. Nota: direcciones y direcciones relativas están en formato hexadecimal.
Before GC
ascending: 0x782322b20, +18, +18, +18, +18, +18, +18, +18, +18, +18, +18, +18, +18, +18, +18, +18
descending: 0x782322e58, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18
shuffled: 0x782322ec0, +78, -30, +90, -c0, +18, +90, +a8, -30, -d8, +f0, -30, -90, +60, -48, +60
After GC
ascending: 0x686811590, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18
descending: 0x686811410, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18
shuffled: 0x686811290, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18
o, a veces
Before GC
ascending: 0x782322b20, +18, +18, +18, +18, +18, +18, +18, +18, +18, +18, +18, +18, +18, +18, +18
descending: 0x782322e58, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18, -18
shuffled: 0x782323028, -168, +150, -d8, -30, +60, +18, +30, +30, +18, -108, +30, -48, +78, +78, -30
After GC
ascending: 0x6868143c8, +4db0, +7120, -bd90, +bda8, -bd90, +4d40, +18, +18, -12710, +18, +80, +18, +ffa8, +220, +6b40
descending: 0x68681d968, +18, +d0, +e0, -165d0, +a8, +fea8, +c110, -5230, -d658, +6bd0, +be10, +1b8, +75e0, -19f68, +19f80
shuffled: 0x686823938, -129d8, +129f0, -17860, +4e88, +19fe8, -1ee58, +18, +18, +bb00, +6a78, -d648, -4e18, +4e40, +133e0, -c770
especifique ¿qué quiere decir con la dirección? Dirección en la memoria? Garbage collector-id? – yankee
¿Por qué lo necesitas? – jarnbjo
cualquiera de las direcciones en la memoria o el recolector de basura id –