Exception Back

Exception & Error

• Throwable: The Throwable class is the superclass of all errors and exceptions in the Java language. Only objects that are instances of this class (or one of its subclasses) are thrown by the Java Virtual Machine or can be thrown by the Java throw statement. Similarly, only this class or one of its subclasses can be the argument type in a catch clause.

Throwable

Exception

Error

Exception

• Exception是可控或不可控的
• Exception通常是由于程序员的错误所导致的
• Exception应该应用级别就要处理

Error

• Error总是不可控的
• Error通常是由于系统的错误所导致的
• Error应该在系统级别处理

Checked Exception & Unchecked Exception

• Checked Exception: 指可以通過代碼處理的異常
• Unchecked Exception: 指並不能通過代碼處理的異常(通常指RuntimeException)

Syntax

try
{
    //Something will throw exceptions
    Exception e = new IOExcetpion;
    throw e;    //throw an Exception instance and goto 1:
}
//...
catch(IOException e)    //Smaller Exception must be before the bigger one
{
1:    e.printStackTrace();    //Trace the throw of Exceptions and goto 2:
}
catch(Exception e)
{
    e.printStackTrace();
    throw e;    //throw this exception to upper level 
}
finally
{
2:    //Something must be done even if there is an exception
}

throws specifier

public void method() throws IOException
{
    //means that method will probably throw an IOException
}