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前言：

java源码阅读，看看是怎么组织起来表达逻辑的，菜鸟笔记。

1.connection接口作数据库连接对象

1.1一阵土话

类a中有接口A作属性Field，接口A中定义了抽象方法aM，规定了返回值是接口B

调用：类a对象.接口A对象(接口实例化).aM(接口方法)，返回值接口B的实现类对象(aM的返回值是对象)

1.2原java语句在这里：

        //获取数据库的连接对象Connection conn=DriverManager.getConnection("jdbc:mysql://localhost:3306/db3","root","root");

1.3解读：DriverManager.getConnection ---DriverManager的静态方法getConnection

getConnection方法原型：

    public static Connection getConnection(String url,String user, String password) throws SQLException {java.util.Properties info = new java.util.Properties();if (user != null) {info.put("user", user);}if (password != null) {info.put("password", password);}return (getConnection(url, info, Reflection.getCallerClass()));}

查看return内容： return (getConnection(url, info, Reflection.getCallerClass()));

继续查看getConnection()方法

    private static Connection getConnection(String url, java.util.Properties info, Class<?> caller) throws SQLException {/** When callerCl is null, we should check the application's* (which is invoking this class indirectly)* classloader, so that the JDBC driver class outside rt.jar* can be loaded from here.*/ClassLoader callerCL = caller != null ? caller.getClassLoader() : null;synchronized(DriverManager.class) {// synchronize loading of the correct classloader.if (callerCL == null) {callerCL = Thread.currentThread().getContextClassLoader();}}if(url == null) {throw new SQLException("The url cannot be null", "08001");}println("DriverManager.getConnection(\"" + url + "\")");// Walk through the loaded registeredDrivers attempting to make a connection.// Remember the first exception that gets raised so we can reraise it.SQLException reason = null;for(DriverInfo aDriver : registeredDrivers) {// If the caller does not have permission to load the driver then// skip it.if(isDriverAllowed(aDriver.driver, callerCL)) {try {println("    trying " + aDriver.driver.getClass().getName());Connection con = aDriver.driver.connect(url, info);if (con != null) {// Success!println("getConnection returning " + aDriver.driver.getClass().getName());return (con);}} catch (SQLException ex) {if (reason == null) {reason = ex;}}} else {println("    skipping: " + aDriver.getClass().getName());}}// if we got here nobody could connect.if (reason != null)    {println("getConnection failed: " + reason);throw reason;}println("getConnection: no suitable driver found for "+ url);throw new SQLException("No suitable driver found for "+ url, "08001");}

找到返回值项return(con);

       for(DriverInfo aDriver : registeredDrivers) {// If the caller does not have permission to load the driver then// skip it.if(isDriverAllowed(aDriver.driver, callerCL)) {try {println("    trying " + aDriver.driver.getClass().getName());Connection con = aDriver.driver.connect(url, info);if (con != null) {// Success!println("getConnection returning " + aDriver.driver.getClass().getName());return (con);}} catch (SQLException ex) {if (reason == null) {reason = ex;}}} else {println("    skipping: " + aDriver.getClass().getName());}}

其中

 Connection con = aDriver.driver.connect(url, info);

就是需要的结果，而这一段可以衔接上1.1，分析如下：

DriverInfo类，包含了接口Drive

class DriverInfo {final Driver driver;DriverAction da;DriverInfo(Driver driver, DriverAction action) {this.driver = driver;da = action;}

 接口里有抽象方法connect，返回值是接口对象connection

public interface Driver {Connection connect(String url, java.util.Properties info)throws SQLException;

aDriver是DriverInfo对象，driver是Driver接口类型的属性，connect是Driver接口方法

  for(DriverInfo aDriver : registeredDrivers) {// If the caller does not have permission to load the driver then// skip it.if(isDriverAllowed(aDriver.driver, callerCL)) {try {println("    trying " + aDriver.driver.getClass().getName());Connection con = aDriver.driver.connect(url, info);if (con != null) {// Success!println("getConnection returning " + aDriver.driver.getClass().getName());return (con);}

如此可以返回一个Connection接口的实现类对象

小结：java里常用接口来实现目的，而不一定在意其具体实现类是什么。

            Java里数据传递基本是以对象进行的。