Learning From Code: Fast Random Access

Marker interfaces do not define behavior directly, instead they "mark" a class as having a particular capability. In the case of Serializable the interface specifies that if the class is serialized using the serialization I/O classes, then a NotSerializableException will not be thrown (unless the object contains some other class that cannot be serialized). Cloneable similarly indicates that the use of the Object.clone() method for a Cloneable class will not throw a CloneNotSupportedException.

The RandomAccessinterface identifies that a particular java.util.List implementation has fast random access. More accurately, the RandomAccess interface identifies List implementations which are faster to iterate using the List.get() method rather than using the Iterator.next() method.

However, when you want to iterate List classes, then you can optimize the iteration speed by using RandomAccess

Many of the utility methods in Collections class use a variant of an algorithm depending on whether or not the object is a RandomAccess object.

    public static int binarySearch(List list, Object key) {
        if (list instanceof RandomAccess || list.size() < BINARYSEARCH_THRESHOLD)
            return indexedBinarySearch(list, key);
        else
            return iteratorBinarySearch(list, key);
    }

   public static void fill(List list, Object obj) {
        int size = list.size();


        if (size <  FILL_THRESHOLD || list instanceof RandomAccess) {
            for (int i=0; i< size; i++)
                list.set(i, obj);
        } else {
            ListIterator itr = list.listIterator();
            for (int i=0; i< size; i++) {
                itr.next();
                itr.set(obj);
            }
        }
    }

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