Class InstructionHandle

java.lang.Object
org.apache.bcel.generic.InstructionHandle
Direct Known Subclasses:
BranchHandle
public class InstructionHandle extends Object
Instances of this class give users a handle to the instructions contained in an InstructionList. Instruction objects may be used more than once within a list, this is useful because it saves memory and may be much faster. Within an InstructionList an InstructionHandle object is wrapped around all instructions, that is, it implements a cell in a doubly-linked list. From the outside only the next and the previous instruction (handle) are accessible. One can traverse the list via an Enumeration returned by InstructionList.elements().
See Also:

  • Field Details

  • Constructor Details

  • Method Details

    • accept

      public void accept(Visitor v)
      Convenience method, simply calls accept() on the contained instruction.
      Parameters:
      v - Visitor object.

    • addAttribute

      public void addAttribute(Object key, Object attr)
      Add an attribute to an instruction handle.
      Parameters:
      key - the key object to store/retrieve the attribute.
      attr - the attribute to associate with this handle.

    • addHandle

      @Deprecated protected void addHandle()
      Deprecated.
      Does nothing as of 6.3.1.
      Does nothing.

    • addTargeter

      public void addTargeter(InstructionTargeter t)
      Denote this handle is being referenced by t.
      Parameters:
      t - the instruction targeter.

    • getAttribute

      public Object getAttribute(Object key)
      Gets attribute of an instruction handle.
      Parameters:
      key - the key object to store/retrieve the attribute.
      Returns:
      the attribute value.

    • getAttributes

      public Collection<Object> getAttributes()
      Gets all attributes associated with this handle.
      Returns:
      all attributes associated with this handle.

    • getInstruction

      public final Instruction getInstruction()
      Gets the instruction.
      Returns:
      the instruction.

    • getNext

      public final InstructionHandle getNext()
      Gets the next instruction handle.
      Returns:
      the next instruction handle.

    • getPosition

      public int getPosition()
      Gets the position.
      Returns:
      the position, the byte code offset of the contained instruction. This is accurate only after InstructionList.setPositions() has been called.

    • getPrev

      public final InstructionHandle getPrev()
      Gets the previous instruction handle.
      Returns:
      the previous instruction handle.

    • getTargeters

      public InstructionTargeter[] getTargeters()
      Gets the targeters.
      Returns:
      null, if there are no targeters.

    • hasTargeters

      public boolean hasTargeters()
      Checks if this handle has targeters.
      Returns:
      true if this handle has targeters, false otherwise.

    • removeAllTargeters

      public void removeAllTargeters()
      Remove all targeters, if any.

    • removeAttribute

      public void removeAttribute(Object key)
      Delete an attribute of an instruction handle.
      Parameters:
      key - the key object to retrieve the attribute.

    • removeTargeter

      public void removeTargeter(InstructionTargeter t)
      Denote this handle isn't referenced anymore by t.
      Parameters:
      t - the instruction targeter.

    • setInstruction

      public void setInstruction(Instruction i)
      Replace current instruction contained in this handle. Old instruction is disposed using Instruction.dispose().
      Parameters:
      i - the new instruction.

    • swapInstruction

      public Instruction swapInstruction(Instruction i)
      Temporarily swap the current instruction, without disturbing anything. Meant to be used by a debugger, implementing breakpoints. Current instruction is returned.

      Warning: if this is used on a BranchHandle then some methods such as getPosition() will still refer to the original cached instruction, whereas other BH methods may affect the cache and the replacement instruction.

      Parameters:
      i - the replacement instruction.
      Returns:
      the old instruction.

    • toString

      public String toString()
      Gets a string representation of the contained instruction.
      Overrides:
      toString in class Object
      Returns:
      a string representation of the contained instruction.

    • toString

      public String toString(boolean verbose)
      Gets a verbose string representation of the contained instruction.
      Parameters:
      verbose - whether to be verbose.
      Returns:
      a (verbose) string representation of the contained instruction.

    • updatePosition

      protected int updatePosition(int offset, int maxOffset)
      Called by InstructionList.setPositions when setting the position for every instruction. In the presence of variable length instructions 'setPositions()' performs multiple passes over the instruction list to calculate the correct (byte) positions and offsets by calling this function.
      Parameters:
      offset - additional offset caused by preceding (variable length) instructions.
      maxOffset - the maximum offset that may be caused by these instructions.
      Returns:
      additional offset caused by possible change of this instruction's length.