org.h2.mvstore.Cursor Maven / Gradle / Ivy
/*
* Copyright 2004-2019 H2 Group. Multiple-Licensed under the MPL 2.0,
* and the EPL 1.0 (https://h2database.com/html/license.html).
* Initial Developer: H2 Group
*/
package org.h2.mvstore;
import java.util.Iterator;
import java.util.NoSuchElementException;
/**
* A cursor to iterate over elements in ascending order.
*
* @param the key type
* @param the value type
*/
public class Cursor implements Iterator {
private final K to;
private CursorPos cursorPos;
private CursorPos keeper;
private K current;
private K last;
private V lastValue;
private Page lastPage;
public Cursor(Page root, K from) {
this(root, from, null);
}
public Cursor(Page root, K from, K to) {
this.cursorPos = traverseDown(root, from);
this.to = to;
}
@Override
@SuppressWarnings("unchecked")
public boolean hasNext() {
if (cursorPos != null) {
while (current == null) {
Page page = cursorPos.page;
int index = cursorPos.index;
if (index >= (page.isLeaf() ? page.getKeyCount() : page.map.getChildPageCount(page))) {
CursorPos tmp = cursorPos;
cursorPos = cursorPos.parent;
tmp.parent = keeper;
keeper = tmp;
if(cursorPos == null)
{
return false;
}
} else {
while (!page.isLeaf()) {
page = page.getChildPage(index);
if (keeper == null) {
cursorPos = new CursorPos(page, 0, cursorPos);
} else {
CursorPos tmp = keeper;
keeper = keeper.parent;
tmp.parent = cursorPos;
tmp.page = page;
tmp.index = 0;
cursorPos = tmp;
}
index = 0;
}
if (index < page.getKeyCount()) {
K key = (K) page.getKey(index);
if (to != null && page.map.getKeyType().compare(key, to) > 0) {
return false;
}
current = last = key;
lastValue = (V) page.getValue(index);
lastPage = page;
}
}
++cursorPos.index;
}
}
return current != null;
}
@Override
public K next() {
if(!hasNext()) {
throw new NoSuchElementException();
}
current = null;
return last;
}
/**
* Get the last read key if there was one.
*
* @return the key or null
*/
public K getKey() {
return last;
}
/**
* Get the last read value if there was one.
*
* @return the value or null
*/
public V getValue() {
return lastValue;
}
/**
* Get the page where last retrieved key is located.
*
* @return the page
*/
Page getPage() {
return lastPage;
}
/**
* Skip over that many entries. This method is relatively fast (for this map
* implementation) even if many entries need to be skipped.
*
* @param n the number of entries to skip
*/
public void skip(long n) {
if (n < 10) {
while (n-- > 0 && hasNext()) {
next();
}
} else if(hasNext()) {
assert cursorPos != null;
CursorPos cp = cursorPos;
CursorPos parent;
while ((parent = cp.parent) != null) cp = parent;
Page root = cp.page;
@SuppressWarnings("unchecked")
MVMap map = (MVMap) root.map;
long index = map.getKeyIndex(next());
last = map.getKey(index + n);
this.cursorPos = traverseDown(root, last);
}
}
@Override
public void remove() {
throw DataUtils.newUnsupportedOperationException(
"Removal is not supported");
}
/**
* Fetch the next entry that is equal or larger than the given key, starting
* from the given page. This method retains the stack.
*
* @param p the page to start from
* @param key the key to search, null means search for the first key
*/
private static CursorPos traverseDown(Page p, Object key) {
CursorPos cursorPos = key == null ? p.getPrependCursorPos(null) : CursorPos.traverseDown(p, key);
if (cursorPos.index < 0) {
cursorPos.index = -cursorPos.index - 1;
}
return cursorPos;
}
}