transient Node<K,V>[] table;
static class Node<K,V> implements Map.Entry<K,V> {
    final int hash;
    final K key;
    V value;
    Node<K,V> next;
    ...
}

transient int size;
int threshold;
final float loadFactor;

static final int hash(Object key) {
    int h;
    return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16);
}

SqlSession session = sqlSessionFactory.openSession();
try {
  Blog blog = (Blog) session.selectOne("org.mybatis.example.BlogMapper.selectBlog", 101);
} finally {
  session.close();
}

SqlSession session = sqlSessionFactory.openSession();
try {
  BlogMapper mapper = session.getMapper(BlogMapper.class);
  Blog blog = mapper.selectBlog(101);
} finally {
  session.close();
}

sqlSessionTemplate.selectOne("com.jh.dao.BlogDao.selectBlog", id);

public class SqlSessionTemplate implements SqlSession, DisposableBean {
  private final SqlSessionFactory sqlSessionFactory;
  private final ExecutorType executorType;
  private final SqlSession sqlSessionProxy;
  private final PersistenceExceptionTranslator exceptionTranslator;
  ......
  public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType,
      PersistenceExceptionTranslator exceptionTranslator) {
    notNull(sqlSessionFactory, "Property 'sqlSessionFactory' is required");
    notNull(executorType, "Property 'executorType' is required");
    this.sqlSessionFactory = sqlSessionFactory;
    this.executorType = executorType;
    this.exceptionTranslator = exceptionTranslator;
    this.sqlSessionProxy = (SqlSession) newProxyInstance(
        SqlSessionFactory.class.getClassLoader(),
        new Class[] { SqlSession.class },
        new SqlSessionInterceptor());
  }
  ......
  @Override
  public <T> T selectOne(String statement) {
    return this.sqlSessionProxy.<T> selectOne(statement);
  }
  ......
  private class SqlSessionInterceptor implements InvocationHandler {
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
      SqlSession sqlSession = getSqlSession(
          SqlSessionTemplate.this.sqlSessionFactory,
          SqlSessionTemplate.this.executorType,
          SqlSessionTemplate.this.exceptionTranslator);
      try {
        Object result = method.invoke(sqlSession, args);
        if (!isSqlSessionTransactional(sqlSession, SqlSessionTemplate.this.sqlSessionFactory)) {
          // force commit even on non-dirty sessions because some databases require
          // a commit/rollback before calling close()
          sqlSession.commit(true);
        }
        return result;
      } catch (Throwable t) {
        Throwable unwrapped = unwrapThrowable(t);
        if (SqlSessionTemplate.this.exceptionTranslator != null && unwrapped instanceof PersistenceException) {
          // release the connection to avoid a deadlock if the translator is no loaded. See issue #22
          closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
          sqlSession = null;
          Throwable translated = SqlSessionTemplate.this.exceptionTranslator.translateExceptionIfPossible((PersistenceException) unwrapped);
          if (translated != null) {
            unwrapped = translated;
          }
        }
        throw unwrapped;
      } finally {
        if (sqlSession != null) {
          closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
        }
      }
    }
  }

public class DefaultSqlSession implements SqlSession {
    private Configuration configuration;
    private Executor executor;
    private boolean autoCommit;
    private boolean dirty;
    private List<Cursor<?>> cursorList;
    ...
}

public class CachingExecutor implements Executor {
  private Executor delegate;
  private TransactionalCacheManager tcm = new TransactionalCacheManager();
  ...
}

public enum ExecutorType {
  SIMPLE, REUSE, BATCH
}

public int update(Blog blog) {
  return sqlSessionTemplate.update("com.jh.dao.BlogDao.update", blog);
}

@Mapper
public interface CityMapper {
  @Select("select * from city where state = #{state}")
  City findByState(@Param("state") String state);
}

public class MapperProxy<T> implements InvocationHandler, Serializable {
  private final SqlSession sqlSession;
  private final Class<T> mapperInterface;
  private final Map<Method, MapperMethod> methodCache;
  ...
  @Override
  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    ...
  }

transient int size = 0;
/**
 * Pointer to first node.
 * Invariant: (first == null && last == null) ||
 *            (first.prev == null && first.item != null)
 */
transient Node<E> first;
/**
 * Pointer to last node.
 * Invariant: (first == null && last == null) ||
 *            (last.next == null && last.item != null)
 */
transient Node<E> last;

private static class Node<E> {
    E item;
    Node<E> next;
    Node<E> prev;
    Node(Node<E> prev, E element, Node<E> next) {
        this.item = element;
        this.next = next;
        this.prev = prev;
    }
}

void linkLast(E e) {
    final Node<E> l = last;
    final Node<E> newNode = new Node<>(l, e, null);
    last = newNode;
    if (l == null)
        first = newNode;
    else
        l.next = newNode;
    size++;
    modCount++;
}

public boolean remove(Object o) {
    if (o == null) {
        for (Node<E> x = first; x != null; x = x.next) {
            if (x.item == null) {
                unlink(x);
                return true;
            }
        }
    } else {
        for (Node<E> x = first; x != null; x = x.next) {
            if (o.equals(x.item)) {
                unlink(x);
                return true;
            }
        }
    }
    return false;
}
E unlink(Node<E> x) {
    // assert x != null;
    final E element = x.item;
    final Node<E> next = x.next;
    final Node<E> prev = x.prev;
    if (prev == null) {
        first = next;
    } else {
        prev.next = next;
        x.prev = null;
    }
    if (next == null) {
        last = prev;
    } else {
        next.prev = prev;
        x.next = null;
    }
    x.item = null;
    size--;
    modCount++;
    return element;
}

public E get(int index) {
    checkElementIndex(index);
    return node(index).item;
}
Node<E> node(int index) {
    // assert isElementIndex(index);
    if (index < (size >> 1)) {
        Node<E> x = first;
        for (int i = 0; i < index; i++)
            x = x.next;
        return x;
    } else {
        Node<E> x = last;
        for (int i = size - 1; i > index; i--)
            x = x.prev;
        return x;
    }
}

private class ListItr implements ListIterator<E> {
    private Node<E> lastReturned;
    private Node<E> next;
    private int nextIndex;
    private int expectedModCount = modCount;
    ListItr(int index) {
        // assert isPositionIndex(index);
        next = (index == size) ? null : node(index);
        nextIndex = index;
    }
    public boolean hasNext() {
        return nextIndex < size;
    }
    public E next() {
        checkForComodification();
        if (!hasNext())
            throw new NoSuchElementException();
        lastReturned = next;
        next = next.next;
        nextIndex++;
        return lastReturned.item;
    }
    public boolean hasPrevious() {
        return nextIndex > 0;
    }
    public E previous() {
        checkForComodification();
        if (!hasPrevious())
            throw new NoSuchElementException();
        lastReturned = next = (next == null) ? last : next.prev;
        nextIndex--;
        return lastReturned.item;
    }
    public int nextIndex() {
        return nextIndex;
    }
    public int previousIndex() {
        return nextIndex - 1;
    }
    public void remove() {
        checkForComodification();
        if (lastReturned == null)
            throw new IllegalStateException();
        Node<E> lastNext = lastReturned.next;
        unlink(lastReturned);
        if (next == lastReturned)
            next = lastNext;
        else
            nextIndex--;
        lastReturned = null;
        expectedModCount++;
    }
    public void set(E e) {
        if (lastReturned == null)
            throw new IllegalStateException();
        checkForComodification();
        lastReturned.item = e;
    }
    public void add(E e) {
        checkForComodification();
        lastReturned = null;
        if (next == null)
            linkLast(e);
        else
            linkBefore(e, next);
        nextIndex++;
        expectedModCount++;
    }
    public void forEachRemaining(Consumer<? super E> action) {
        Objects.requireNonNull(action);
        while (modCount == expectedModCount && nextIndex < size) {
            action.accept(next.item);
            lastReturned = next;
            next = next.next;
            nextIndex++;
        }
        checkForComodification();
    }
    final void checkForComodification() {
        if (modCount != expectedModCount)
            throw new ConcurrentModificationException();
    }
}

/**
* The array buffer into which the elements of the ArrayList are stored.
* The capacity of the ArrayList is the length of this array buffer. Any
* empty ArrayList with elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA
* will be expanded to DEFAULT_CAPACITY when the first element is added.
*/
transient Object[] elementData; // non-private to simplify nested class access
/**
* The size of the ArrayList (the number of elements it contains).
*
* @serial
*/
private int size;

protected transient int modCount = 0;

public E get(int index) {
    rangeCheck(index);
    return elementData(index);
}

public E set(int index, E element) {
    rangeCheck(index);
    E oldValue = elementData(index);
    elementData[index] = element;
    return oldValue;
}

/**
 * Appends the specified element to the end of this list.
 *
 * @param e element to be appended to this list
 * @return <tt>true</tt> (as specified by {@link Collection#add})
 */
public boolean add(E e) {
    ensureCapacityInternal(size + 1);  // Increments modCount!!
    elementData[size++] = e;
    return true;
}

/**
 * Removes the element at the specified position in this list.
 * Shifts any subsequent elements to the left (subtracts one from their
 * indices).
 *
 * @param index the index of the element to be removed
 * @return the element that was removed from the list
 * @throws IndexOutOfBoundsException {@inheritDoc}
 */
public E remove(int index) {
    rangeCheck(index);
    modCount++;
    E oldValue = elementData(index);
    int numMoved = size - index - 1;
    if (numMoved > 0)
        System.arraycopy(elementData, index+1, elementData, index,
                         numMoved);
    elementData[--size] = null; // clear to let GC do its work
    return oldValue;
}

private class Itr implements Iterator<E>

public Iterator<E> iterator() {
    return new Itr();
}

// 错误的代码 java.util.ConcurrentModificationException
public static void main(String[] args) {
    List<String> list = new ArrayList<>();
    list.add("1");
    list.add("2");
    list.add("3");
    list.add("4");
    for (String s : list) {
        if ("2".equals(s)) {
            list.remove(s);
        }
    }
}

public boolean add(E e) {
    final ReentrantLock lock = this.lock;
    lock.lock();
    try {
        Object[] elements = getArray();
        int len = elements.length;
        Object[] newElements = Arrays.copyOf(elements, len + 1);
        newElements[len] = e;
        setArray(newElements);
        return true;
    } finally {
        lock.unlock();
    }
}

public E get(int index) {
    return get(getArray(), index);
}
private E get(Object[] a, int index) {
    return (E) a[index];
}