- When a program is
loaded into
memory, the
memory will
contain:
- The computer instructions
used to execute the
statements in the
computer program
- The class variables (which exists for the entire execution of the program)
Graphically:
- The computer instructions
used to execute the
statements in the
computer program
- From CS170:
- The local variables
and parameter variables
of a
method are
destroyed when:
- The method exits (= returns)
- The local variables
and parameter variables
of a
method are
created when:
- The method starts executing
- The local variables
and parameter variables
of a
method are
destroyed when:
- A variable is
created by:
- Reserving
memory cells for the variable
Graphically:
The computer will never re-use the reserved memory cells for another variable !!!
- Reserving
memory cells for the variable
- A variable is
destroyed by:
- Un-reserving the
memory cells
used by the variable
Graphically:
- Note:
- The un-reserved memory cells can now be re-used for other variables !!!
- Un-reserving the
memory cells
used by the variable
- Memory management:
- Variables are
not stored in the
memory in a
haphazard manner
- The variables are stored in an organized manner for efficiency !!!
- Variables are
not stored in the
memory in a
haphazard manner
- Important fact:
- Variables are organized using the "existential" characteristics of the variables !!!
- Characteristics about
the variables in
Java:
- Parameter variables and
local variables are
created/destroyed in a
orderly fashion
- The
parameter variables and
local variables are
created when a
method is
invoked
- The parameter variables and local variables are destroyed when a method is exited
- The
parameter variables and
local variables are
created when a
method is
invoked
- Instance variables are
created/destroyed in an
unpredictable manner
- Instance variables
are created when
the program
executes a
new
operation
- We cannot predict when the program will execute a new operation !!!!
- Instance variables
are created when
the program
executes a
new
operation
- Parameter variables and
local variables are
created/destroyed in a
orderly fashion
-
Important note:
- We do not have to
consider the
class variables, because
they have been
created already
during the program loading step:
- We do not have to
consider the
class variables, because
they have been
created already
during the program loading step:
- The program is
organized into
the memory as follows:
Explanation:
- Fixed area:
- contains (program) instructions
and class variables
These memory cells will be used (= reserved) for the entire duration of the program
- contains (program) instructions
and class variables
- Heap:
- conatins the instance variables
Memory cells in the heap are reserved when an instance variable is created
Memory cells in the heap are un-reserved when an instance variable is destroyed (= garbage collected)
- conatins the instance variables
- Stack:
- conatins the parameter and
local variables
Memory cells in the stack are reserved when an parameter/local variable is created
Memory cells in the stack are un-reserved when an parameter/local variable is destroyed (= garbage collected)
- Due to call/return sequence
of the
methods, the
variables will be
destroyed in a
LIFO manner
The behavior is same as a stack !!!
More about this later in the course
- Due to call/return sequence
of the
methods, the
variables will be
destroyed in a
LIFO manner
- conatins the parameter and
local variables
- Fixed area:
- When a program
is loaded into
memory:
- The instructions are stored
- The class variables are created
Schematically:
- When the program
creates an
instance variable
(using new), the
instance variable is
stored in the
heap:
- When the program invokes
a method,
the
parameter variables and
the local variables of
the method
are
stored in the
stack:
