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Defining the head reference variable to a link list in assembler

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• The head variable of a linked list
  • A linked list is dynamically created

    That means that the elements of a linked list does not exist when the program starts executing

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  • The only variable that is defined in a program that uses linked lists is a reference variable that is often called head.

    In Java, this variable is defined as follows:

    List head;

    The user-defined Java class class will contain the definition of a list structure.

    Regardless of the list structure, the variable head defined by

    List head;

    is a reference variable in Java

    A reference variable in Java contains the memory address !!! A memory address is a 32 bits binary number used to identify a memory location

    We has discussed the reference concept in CS255 already, here is the webpage if you need a review: click here

    Very important fact:

    The head variable used to point to the first element in a linked list: is not a linked list object !!! It's a variable that only contains a memory address !!! (You can see this visually in the figure above; the head variable in the illustration contains the memory address 7000)

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• How to define the head variable of a linked list
  • The Java definition:

    List head;

    corresponds to the following (ARM) assembler directives:

    head: .skip 4 // Reserve 4 bytes to store a memory address // Memory address in ARM consists of 32 bits