Capacity field vs. array length

Queue.java

package bench;

import org.openjdk.jmh.annotations.Benchmark;
import org.openjdk.jmh.annotations.Param;
import org.openjdk.jmh.annotations.Scope;
import org.openjdk.jmh.annotations.Setup;
import org.openjdk.jmh.annotations.State;
import org.openjdk.jmh.annotations.Threads;
import sun.misc.Unsafe;

import java.lang.reflect.Field;

@State(Scope.Benchmark)
@Threads(4)
public class Queue {
    private static final Unsafe unsafe = getUnsafe();
    private static final long base = unsafe.arrayBaseOffset(Object[].class);
    private static final int scale = unsafe.arrayIndexScale(Object[].class);

    private Object[] buffer;
    private int capacity;

    @Param({"0", "9"})
    private volatile int index;

    @Setup
    public void setup() {
        buffer = new Object[10];
        capacity = buffer.length;
    }

    @Benchmark
    public void arrayLength() {
        int index = this.index;
        if (index < 0 || index >= buffer.length) {
            throw new ArrayIndexOutOfBoundsException();
        }
        unsafe.putObjectVolatile(buffer, base + index * scale, "123");
    }

    @Benchmark
    public void capacityField() {
        int index = this.index;
        if (index < 0 || index >= capacity) {
            throw new ArrayIndexOutOfBoundsException();
        }
        unsafe.putObjectVolatile(buffer, base + index * scale, "123");
    }

    private static Unsafe getUnsafe() {
        try {
            Field f = Unsafe.class.getDeclaredField("theUnsafe");
            f.setAccessible(true);
            return (Unsafe) f.get(null);
        } catch (IllegalAccessException | NoSuchFieldException e) {
            throw new AssertionError("Should not happen");
        }
    }
}

results.txt

Benchmark            (index)   Mode  Cnt      Score      Error   Units
Queue.arrayLength          0  thrpt    5  49183,203 ±  521,193  ops/ms
Queue.arrayLength          9  thrpt    5  83877,975 ± 1261,613  ops/ms
Queue.capacityField        0  thrpt    5  84168,673 ±  898,044  ops/ms
Queue.capacityField        9  thrpt    5  83964,912 ± 1790,430  ops/ms