用JD-eclipse反编译出现 throw new RuntimeException("Stub!")

Question

是什么意思 方法名 参数都有 方法体了就一句
public static int rgb(int red, int green, int blue) {
throw new RuntimeException("Stub!");
} 这是什么意思，他也不报错，方法也不抛异常 （献给5 分 答案采纳后追加50分）
方法体力抛了异常 不应该
public static int rgb(int red, int green, int blue) throws RuntimeException {
throw new RuntimeException("Stub!");
} 这么写么？ 这个是反编译出来的，我怀疑是不是反编译工具的问题， 怎么可能代码里就这么一句不着调的代码···

Answer 1

An interesting note on Android SDK is that the code in android.jar is stubbed out. This because the code inside the jar is never runs, so there’s no reason to make the SDK bigger because of this. To better undersand, if you look at these classes using a decompiler (with jad for example) you will only see: public void something(…){ throw new RuntimeException(“Stub!”); }. This means that you use android.jar only for the purpose of compiling the code, use autocomplete and imports in Eclipse.
Moreover, android.jar contains only the APIs exposed for the level of applications development. It’s a promise from Google that if you compile your application using this jar, you are guaranteed your application will run in future versions of Android. There is a part of the compilation process in the Android system that removes methods and classes of API. It’s used internally by the framework and should not be used for an Android developer. Why does Google do it? Well, I believe it’s because Google needs to write too much code to get API exposed. A lot of code starting in the hardware until to get a high-level API, which can be changed from one version to another, even codes that may no longer exist in future versions.

Answer 2

javaDB其实就是Derby，它并不是一个新的数据库产品,它是由IBM捐献给Apache的DB项目的一个纯Java数据库,JDK6.0里面带的这个Derby的版本是 10.2.1.7,支持存储过程和触发器;有两种运行模式,一种是作为嵌入式数据库,另一种是作为网络数据库,前者的数据库服务器和客户端都在同一个 JVM里面运行,后者允许数据库服务器端和客户端不在同一个JVM里面,而且允许这两者在不同的物理机器上.值得注意的是JDK6里面的这个Derby支持JDK6的新特性JDBC 4.0规范(JSR 221),现在我们如果要练习JDBC的用法,没有必要单独装一个数据库产品了,直接用Derby就行.

1、本身没有操作界面，可以用第三方工具来管理（也就是你说的操作界面），Aqua Data Studio 具备管理功能的用于 Apache Derby 关系数据库的管理工具和数据库查询工具。直观管理功能让用户能够浏览和修改数据库结构，包括架构对象和数据库存储，以及维护数据库安全。集成查询工具让您能够迅速创建、编辑和执行 SQL 查询与脚本。Aqua Data Studio 进一步提供导入与导出工具，从而轻松地将数据移入和移出不同的数据格式及 Apache Derby 数据库。集成在这些工具内的是库浏览器 (Repository Browser)，拥有 CVS 和 Subversion (SVN) 的完整来源控制客户端。

2、两者的区别，简单的说，就是javaDB是一个简化轻量级数据库，适合小型系统的小规模测试用，完全可以跑在内存里的数据库，它只有3M大小，而MySQL则是可以应用部署大型系统的数据库，功能更多更全，也更稳定，是用范围更广。

3、下面是个使用derby的简单例子:
首先导入JAR包:derby.jar,如果你装的是JDK6,在C:\Program Files\Sun\JavaDB\lib目录下就可以找到.
然后就要创建数据库了:

代码
private Connection getConnection() throws SQLException {
Connection connection = DriverManager
.getConnection("jdbc:derby:userDB;create=true;user=test;password=test");
connection.setAutoCommit(false);
return connection;
}

其中userDB是要连接数据库的名字,create=true表示如果该数据库不存在,则创建该数据库,如果数据库存在,则用用户user=test;密码password=test连接数据库.

有了数据库,接下来该建表了:

代码
private void createTable(Connection connection) throws SQLException {
Statement statement = connection.createStatement();

String sql = "create table USERS("
+ " ID BIGINT not null generated by default as identity,"
+ " USER_NAME VARCHAR(20) not null,"
+ " PASSWORD VARCHAR(20),"
+ " constraint P_KEY_1 primary key (ID))";
statement.execute(sql);

sql = "create unique index USER_NAME_INDEX on USERS ("
+ " USER_NAME ASC)";
statement.execute(sql);

statement.close();
}

创建了 USERS表,包括ID,USER_NAME,PASSWORD三个列,其中ID是主键,其中generated by default as identity 的作用类似sequence,identity是定义自动加一的列,
GENERATED BY ALWAYS AS IDENTITY
GENERATED BY DEFAULT AS IDENTITY
By always和by default是说明生成这个IDENTITY的方式。
By always是完全由系统自动生成。
by default是可以由用户来指定一个值。
编写与USERS表对应的javabean(这个就不多说了),:

代码
public class User implements Serializable {

/**
*
*/
private static final long serialVersionUID = 1L;

private Long id;

private String userName;

private String password;

public Long getId() {
return id;
}

public void setId(Long id) {
this.id = id;
}

public String getUserName() {
return userName;
}

public void setUserName(String userName) {
this.userName = userName;
}

public String getPassword() {
return password;
}

public void setPassword(String password) {
this.password = password;
}
}

接下来就可以就数据库进行增删改查的操作了:

插入数据:

代码
private void create(User user) {
Connection connection = null;

try {
connection = this.getConnection();
PreparedStatement statement = connection
.prepareStatement("insert into users (user_name,password) values(?,?)");

int index = 1;
statement.setString(index++, user.getUserName());
statement.setString(index++, user.getPassword());

statement.execute();

user.setId(this.getId(connection));

connection.commit();
} catch (SQLException e) {
rollback(connection);
throw new RuntimeException(e);
} finally {
if (connection != null) {
close(connection);
}
}
}

代码
private Long getId(Connection connection) throws SQLException {
CallableStatement callableStatement = connection
.prepareCall("values identity_val_local()");

ResultSet resultSet = callableStatement.executeQuery();
resultSet.next();
Long id = resultSet.getLong(1);
resultSet.close();
callableStatement.close();
return id;
}

getId方法是获得系统默认的id值,是通过 identity_val_local()获得的,而函数IDENTITY_VAL_LOCAL()则可以在INSERT语句执行之后，为我们返回刚才系统为id所产生的值.感觉还是有点想sequence的curr_val.

修改数据:

代码

private void update(User user) {
Connection connection = null;

try {
connection = this.getConnection();
PreparedStatement statement = connection
.prepareStatement("update users set user_name=?,password=? where id=?");

int index = 1;
statement.setString(index++, user.getUserName());
statement.setString(index++, user.getPassword());
statement.setLong(index++, user.getId());

statement.execute();

connection.commit();
} catch (SQLException e) {
rollback(connection);
throw new RuntimeException(e);
} finally {
if (connection != null) {
close(connection);
}
}
}

删除数据:

代码

public void delete(Long id) {
Connection connection = null;

try {
connection = this.getConnection();
PreparedStatement statement = connection
.prepareStatement("delete from users where id=?");
statement.setLong(1, id);
statement.execute();
connection.commit();
} catch (SQLException e) {
rollback(connection);
throw new RuntimeException(e);
} finally {
if (connection != null) {
close(connection);
}
}
}

查询数据:

代码
public User findById(Long id) {
Connection connection = null;

try {
connection = this.getConnection();

PreparedStatement statement = connection
.prepareStatement("select user_name,password from users where id=?");
statement.setLong(1, id);
ResultSet resultSet = statement.executeQuery();

User user = null;

if (resultSet.next()) {
user = new User();
user.setId(id);
user.setUserName(resultSet.getString("user_name"));
user.setPassword(resultSet.getString("password"));
}

resultSet.close();
statement.close();
connection.commit();
return user;
} catch (SQLException e) {
throw new RuntimeException(e);
} finally {
if (connection != null) {
close(connection);
}
}
}

Answer 3

意思就是一旦执行到这个方法，就会抛出一个运行时异常，异常信息为Stub!
然后如果你在其他地方调用了这个方法的话，一定能够在try{}catch(Exception e){}中捕获到这个异常。
你方法不报异常是因为你没写对应捕获的代码。本回答被网友采纳