Subclasses of this class are of the following form: * *
* class FooMap
* extends sun.util.PreHashedMap<String>
* {
*
* private FooMap() {
* super(ROWS, SIZE, SHIFT, MASK);
* }
*
* protected void init(Object[] ht) {
* ht[0] = new Object[] { "key-1", value_1 };
* ht[1] = new Object[] { "key-2", value_2,
* new Object { "key-3", value_3 } };
* ...
* }
*
* }The init method is invoked by the PreHashedMap * constructor with an object array long enough for the map's rows. The method * must construct the hash chain for each row and store it in the appropriate * element of the array. * *
Each entry in the map is represented by a unique hash-chain node. The * final node of a hash chain is a two-element object array whose first element * is the entry's key and whose second element is the entry's value. A * non-final node of a hash chain is a three-element object array whose first * two elements are the entry's key and value and whose third element is the * next node in the chain. * *
Instances of this class are mutable and are not safe for concurrent * access. They may be made immutable and thread-safe via the appropriate * methods in the {@link java.util.Collections} utility class. * *
In the JDK build, subclasses of this class are typically created via the
* Hasher program in the make/tools/Hasher directory.
*
* @author Mark Reinhold
* @since 1.5
*
* @see java.util.AbstractMap
*/
public abstract class PreHashedMap This constructor invokes the {@link #init init} method, passing it a
* newly-constructed row array that is rows elements long.
*
* @param rows
* The number of rows in the map
* @param size
* The number of entries in the map
* @param shift
* The value by which hash codes are right-shifted
* @param mask
* The value with which hash codes are masked after being shifted
*/
protected PreHashedMap(int rows, int size, int shift, int mask) {
this.rows = rows;
this.size = size;
this.shift = shift;
this.mask = mask;
this.ht = new Object[rows];
init(ht);
}
/**
* Initializes this map.
*
* This method must construct the map's hash chains and store them into
* the appropriate elements of the given hash-table row array.
*
* @param rows
* The row array to be initialized
*/
protected abstract void init(Object[] ht);
@SuppressWarnings("unchecked")
private V toV(Object x) {
return (V)x;
}
public V get(Object k) {
int h = (k.hashCode() >> shift) & mask;
Object[] a = (Object[])ht[h];
if (a == null) return null;
for (;;) {
if (a[0].equals(k))
return toV(a[1]);
if (a.length < 3)
return null;
a = (Object[])a[2];
}
}
/**
* @throws UnsupportedOperationException
* If the given key is not part of this map's initial key set
*/
public V put(String k, V v) {
int h = (k.hashCode() >> shift) & mask;
Object[] a = (Object[])ht[h];
if (a == null)
throw new UnsupportedOperationException(k);
for (;;) {
if (a[0].equals(k)) {
V ov = toV(a[1]);
a[1] = v;
return ov;
}
if (a.length < 3)
throw new UnsupportedOperationException(k);
a = (Object[])a[2];
}
}
public Set