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Java/Others/FirstFit.java at dev · primary-code-test/Java · GitHub
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FirstFit.java
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package
Others
;
import
java
.
util
.
ArrayList
;
/** @author Dekas Dimitrios */
public
class
FirstFit
{
private
static
final
int
NO_ALLOCATION
=
-
255
;
// if a process has been allocated in position -255,
// it means that it has not been actually allocated.
/**
* Method to find the index of the memory block that is going to fit the given process based on
* the first fit algorithm.
*
* @param blocks: the array with the available memory blocks.
* @param process: the size of the process.
* @return the index of the block that fits, or -255 if no such block exists.
*/
private
static
int
findFirstFit
(
int
[]
blockSizes
,
int
processSize
) {
for
(
int
i
=
0
;
i
<
blockSizes
.
length
;
i
++) {
if
(
blockSizes
[
i
] >=
processSize
) {
return
i
;
}
}
// If there is not a block that can fit the process, return -255 as the result
return
NO_ALLOCATION
;
}
/**
* Method to allocate memory to blocks according to the first fit algorithm. It should return an
* ArrayList of Integers, where the index is the process ID (zero-indexed) and the value is the
* block number (also zero-indexed).
*
* @param sizeOfBlocks: an int array that contains the sizes of the memory blocks available.
* @param sizeOfProcesses: an int array that contains the sizes of the processes we need memory
* blocks for.
* @return the ArrayList filled with Integers repressenting the memory allocation that took place.
*/
static
ArrayList
<
Integer
>
firstFit
(
int
[]
sizeOfBlocks
,
int
[]
sizeOfProcesses
) {
// The array list responsible for saving the memory allocations done by the first-fit algorithm
ArrayList
<
Integer
>
memAlloc
=
new
ArrayList
<>();
// Do this for every process
for
(
int
processSize
:
sizeOfProcesses
) {
int
chosenBlockIdx
=
findFirstFit
(
sizeOfBlocks
,
processSize
);
// Find the index of the memory block going to be used
memAlloc
.
add
(
chosenBlockIdx
);
// Store the chosen block index in the memAlloc array list
if
(
chosenBlockIdx
!=
NO_ALLOCATION
) {
// Only if a block was chosen to store the process in it,
sizeOfBlocks
[
chosenBlockIdx
] -=
processSize
;
// resize the block based on the process size
}
}
return
memAlloc
;
}
/**
* Method to print the memory allocated.
*
* @param memAllocation: an ArrayList of Integer representing the memory allocation done by the
* firstFit method.
*/
public
static
void
printMemoryAllocation
(
ArrayList
<
Integer
>
memAllocation
) {
System
.
out
.
println
(
"Process No.
\t
Block No."
);
System
.
out
.
println
(
"===========
\t
========="
);
for
(
int
i
=
0
;
i
<
memAllocation
.
size
();
i
++) {
System
.
out
.
print
(
" "
+
i
+
"
\t
\t
"
);
if
(
memAllocation
.
get
(
i
) !=
NO_ALLOCATION
)
System
.
out
.
print
(
memAllocation
.
get
(
i
));
else
System
.
out
.
print
(
"Not Allocated"
);
System
.
out
.
println
();
}
}
}
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