✎ javacard:jcvm:6.9.1_exception_handler_info [wiki]

This page is read only. You can view the source, but not change it. Ask your administrator if you think this is wrong.
==== 6.9.1 exception_handler_info ====

The **exception_handler_info** structure is defined as follows: 

The items in the **exception_handler_info** structure are as follows: 

**start_offset, active_length** 

The ****start_offset**** and ****active_length**** pair indicate the active range (try block) an exception handler. The ****start_offset**** item indicates the beginning of the active range while the ****active_length**** item indicates the number of bytes contained in the active range. 

**end_offset** is defined as **start_offset** plus **active_length**. 

The ******start_offset****** item and ******end_offset****** are byte offsets into the **info** item of the Method Component. The value of the ******start_offset****** must be a valid offset into a ****bytecodes**** array of a method_**info** structure to an opcode of an instruction. The value of the ******end_offset****** either must be a valid offset into a ****bytecodes**** array of the same method_**info** structure to an opcode of an instruction, or must be equal to the method's bytecode count, the length of the ****bytecodes**** array of the method_**info** structure. The value of the ******start_offset****** must be less than the value of the ******end_offset******. 

The ****start_offset**** is inclusive and the ****end_offset**** is exclusive; that is, the exception handler must be active while the execution address is within the interval [****start_offset****, ****end_offset****). 

**stop_bit** 

The stop_bit item indicates whether the active range (try block) of this exception handler is contained within or is equal to the active range of any succeeding **exception_handler_info** structures in this **exception_handlers** array. At the Java source level, this indicates whether an active range is nested within another, or has at least one succeeding exception handler associated with the same range. The latter occurs when there is at least one succeeding catch block or a finally block. 

The **stop_bit** item is equal to 1 if the active range does not intersect with a succeeding exception handler's active range, and this exception handler is the last handler applicable to the active range. It is equal to 0 if the active range is contained within the active range of another exception handler, or there is at least one succeeding handler applicable to the same active range. 

The **stop_bit** provides an optimization to be used during the interpretation of the athrow bytecode. As the interpreter searches for an appropriate exception handler, it may terminate the search of the exception handlers in this Method Component under the following conditions: 

  

  *the location of the current program counter is less than the **end_offset** of this exception handler, and    

  *the **stop_bit** of this exception handler is equal to 1.    

When these conditions are satisfied it is guaranteed that none of the succeeding exception handlers in this Method Component will contain an active range appropriate for the current exception. 

In [[6._The_CAP_File_Format| CODE EXAMPLE 6-1]], the **stop_bit** item is set for both the third and fourth handlers. 

**handler_offset** 

The **handler_offset** item represents a byte offset into the info item of the Method Component. It indicates the start of the exception handler. At the Java source level, this is equivalent to the beginning of a catch or finally block. The value of the item must be a valid offset into a bytecodes array of a **method_info** structure to an opcode of an instruction, and must be less than the value of the method's bytecode count. 

**catch_type_index** 

If the value of the **catch_type_index** item is non-zero, it must be a valid index into the ****constant_pool[]**** array of the Constant Pool Component ([[6.7_Constant Pool Component| Section 6.7, Constant Pool Component]]). The ****constant_pool[]**** entry at that index must be a **CONSTANT_Classref_info** structure, representing the class of the exception caught by this **exception_handlers** array entry. 

If the **exception_handlers** table entry represents a finally block, the value of the **catch_type_index** item is zero. In this case the exception handler is called for all exceptions that are thrown within the **start_offset** and **end_offset** range. 

The order of constants in the constant pool is constrained such that all entries referenced by **catch_type_index** items that represent catch block (not finally blocks) are located at non-zero entries.
User Tools

Site Tools

Page Tools
