Unsafe类的问题，arrayIndexScale注释看不懂

Question

/**
 * Report the scale factor for addressing elements in the storage
 * allocation of a given array class.  However, arrays of "narrow" types
 * will generally not work properly with accessors like {@link
 * #getByte(Object, int)}, so the scale factor for such classes is reported
 * as zero.
 *
 * @see #arrayBaseOffset
 * @see #getInt(Object, long)
 * @see #putInt(Object, long, int)
 */
public native int arrayIndexScale(Class<?> arrayClass);

* However, arrays of "narrow" types
* will generally not work properly with accessors like {@link
* #getByte(Object, int)}, so the scale factor for such classes is reported
* as zero.

这块注释啥意思呢？我看不懂，有大神可以举例解答一下吗？

Answer 1

arrayIndexScale获取的是数组对象中元素存储的偏移量。看下面示例，就明白了：

private void arrayTest() {
    String[] array=new String[]{"str1str1str","str2","str3"};
    int baseOffset = unsafe.arrayBaseOffset(String[].class);
    System.out.println(baseOffset);
    int scale = unsafe.arrayIndexScale(String[].class);
    System.out.println(scale);
 
    for (int i = 0; i < array.length; i++) {
        int offset=baseOffset+scale*i;
        System.out.println(offset+" : "+unsafe.getObject(array,offset));
    }
}

结果：