java createStatement（）方法如何返回语句的对象？

Question

根据javadoc，createStatement()方法创建一个Statement实例，用于向数据库发送SQL语句

现在Statement是java.sql包下的interface，我的理解是，不可能在Java中创建接口的实例

那它是怎么工作的？ 我从源头上找到了这个，只是我不明白

/**
 * Creates a <code>Statement</code> object for sending
 * SQL statements to the database.
 * SQL statements without parameters are normally
 * executed using <code>Statement</code> objects. If the same SQL statement
 * is executed many times, it may be more efficient to use a
 * <code>PreparedStatement</code> object.
 * <P>
 * Result sets created using the returned <code>Statement</code>
 * object will by default be type <code>TYPE_FORWARD_ONLY</code>
 * and have a concurrency level of <code>CONCUR_READ_ONLY</code>.
 * The holdability of the created result sets can be determined by
 * calling {@link #getHoldability}.
 *
 * @return a new default <code>Statement</code> object
 * @exception SQLException if a database access error occurs
 * or this method is called on a closed connection
 */
Statement createStatement() throws SQLException;

Answer 1

下面是一些示例代码：

interface IBlammy
{
    public String blam();
}

class BlammyImpl
implements IBlammy
{
    public String blam()
    {
        return "kapow";
    }
}


class Hooty
{
    public IBlammy getStatement()
    {
        return new BlammyImpl();
    }
}

胡闹。getStatement（）返回对实现IBlammy接口的对象的引用

Answer 2

您正在查看Connection的接口的源代码，而不是类。接口不包含任何类型的实现——它们只是定义了一个契约，实现该接口的类必须实现该接口上的所有内容

http://docs.oracle.com/javase/7/docs/api/java/sql/Connection.html