自定义异常类。一、第一种定义方式,继承Exception类public class MyFirstException extends Exception { public MyFirstException() { super(); } public MyFirstException(String msg) { super(msg); } public MyFirstException(String msg, Throwable cause) { super(msg, cause); } public MyFirstException(Throwable cause) { super(cause); } //自定义异常类的主要作用是区分异常发生的位置,当用户遇到 //异常时,根据异常名就可以知道哪里有异常,根据异常提示信 //息进行修改。}
二、 第二种定义方式:继承Throwable 类 public class MySecondException extends Throwable { public MySecondException() { super(); } public MySecondException(String msg) { super(msg); } public MySecondException(String msg, Throwable cause) { super(msg, cause); } public MySecondException(Throwable cause) { super(cause); }}三、测试/** * 自定义异常类的使用 * @author new * */public class TestMyException { public static void firstException() throws MyFirstException{ throw new MyFirstException("\"firstException()\" method occurs an exception!"); } public static void secondException() throws MySecondException{ throw new MySecondException("\"secondException()\" method occurs an exception!"); } public static void main(String[] args) { try { TestMyException.firstException(); TestMyException.secondException(); } catch (MyFirstException e1){ System.out.println("Exception: " + e1.getMessage()); e1.printStackTrace(); } catch (MySecondException e2){ System.out.println("Exception: " + e2.getMessage()); e2.printStackTrace(); } //当一个try块后面跟着多个catch块时,如果发生的异常匹配第一个catch块的参数,便将异常处理权利交给第一个catch块。 //如果发生的异常与第一个catch块不匹配,便看是否与第二个catch块匹配,依次下去,如果到最后依然无法匹配该异常, //便需要在方法声明中添加一条throw语句,将该异常抛出。 //因此,在有多个catch块,而且每次处理的异常类型具有继承关系时,应该首先catch子类异常,再catch父类异常。 //比如,如果MySecondException继承MyFirstException,那么最好将catch (MySecondException e2)放在前面, //把catch (MyFirstException e1)放在后面。}}
异常处理方式:
- OutputStreamWriter out = ...
- java.sql.Connection conn = ...
- try {
- Statement stat = conn.createStatement();
- ResultSet rs = stat.executeQuery(
- "select uid, name from user");
- while (rs.next())
- {
- out.println("ID:" + rs.getString("uid") + ",姓名: " + rs.getString("name"));
- }
- }
- catch(SQLException sqlex)
- {
- out.println("警告:数据不完整");
- throw new ApplicationException("读取数据时出现SQL错误", sqlex);
- }
- catch(IOException ioex)
- {
- throw new ApplicationException("写入数据时出现IO错误", ioex);
- }
- finally
- {
- if (conn != null) {
- try {
- conn.close();
- }
- catch(SQLException sqlex2)
- {
- System.err(this.getClass().getName() + ".mymethod - 不能关闭数据库连接: " + sqlex2.toString());
- }
- }
-
- if (out != null) {
- try {
- out.close();
- }
- catch(IOException ioex2)
- {
- System.err(this.getClass().getName() + ".mymethod - 不能关闭输出文件" + ioex2.toString());
- }
- }
- }