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JavaExercises/Java 3/HW5Lesson.java at master · biblelamp/JavaExercises · GitHub
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/**
* Java. Level 3. Lesson 5. Homework
* We organize races:
* - All racers must start simultaneously
* - At the same time more than half of the riders can not enter the tunnel
* (this is the condition)
* - Determine the winner of the race
* - Only after the finish of the last racer you can report: race is over
* - Try to synchronize all this
*
* @author Sergey Iryupin
* @version Mar 04, 2018
* @link https://github.com/biblelamp
*/
import
java
.
util
.
Arrays
;
import
java
.
util
.
ArrayList
;
import
java
.
util
.
concurrent
.
CountDownLatch
;
// for start/finish
import
java
.
util
.
concurrent
.
Semaphore
;
// for tunnel
public
class
HW5Lesson
{
public
static
final
int
CARS_COUNT
=
4
;
public
static
final
CountDownLatch
START
=
new
CountDownLatch
(
CARS_COUNT
+
1
);
public
static
final
Semaphore
TUNNEL
=
new
Semaphore
(
CARS_COUNT
/
2
,
false
);
public
static
final
CountDownLatch
FINISH
=
new
CountDownLatch
(
CARS_COUNT
);
public
static
void
main
(
String
[]
args
)
throws
InterruptedException
{
System
.
out
.
println
(
"Attention >>> Preparation..."
);
Race
race
=
new
Race
(
new
Road
(
60
),
new
Tunnel
(),
new
Road
(
40
));
Car
[]
cars
=
new
Car
[
CARS_COUNT
];
for
(
int
i
=
0
;
i
<
cars
.
length
;
i
++) {
cars
[
i
] =
new
Car
(
race
,
20
+ (
int
)(
Math
.
random
() *
10
));
new
Thread
(
cars
[
i
]).
start
();
}
while
(
START
.
getCount
() >
1
)
// are the racers ready for the start?
Thread
.
sleep
(
100
);
// wait 100 ms
System
.
out
.
println
(
"Attention >>> The race began!"
);
START
.
countDown
();
// start all the racers
while
(
FINISH
.
getCount
() >
0
);
// this race is over?
System
.
out
.
println
(
"Attention >>> The race is over!"
);
}
}
class
Car
implements
Runnable
{
private
static
int
CARS_COUNT
;
static
{
CARS_COUNT
=
0
;
}
private
Race
race
;
private
int
speed
;
private
String
name
;
public
Car
(
Race
race
,
int
speed
) {
this
.
race
=
race
;
this
.
speed
=
speed
;
this
.
name
=
"Racer #"
+ (++
CARS_COUNT
);
}
public
String
getName
() {
return
name
;
}
public
int
getSpeed
() {
return
speed
;
}
@
Override
public
void
run
() {
try
{
System
.
out
.
println
(
name
+
" is getting ready"
);
Thread
.
sleep
(
500
+ (
int
)(
Math
.
random
() *
800
));
System
.
out
.
println
(
name
+
" is ready ("
+
speed
+
")"
);
HW5Lesson
.
START
.
countDown
();
// we expect the readiness
HW5Lesson
.
START
.
await
();
// of all racers
}
catch
(
InterruptedException
e
) {
e
.
printStackTrace
();
}
for
(
int
i
=
0
;
i
<
race
.
getStages
().
size
();
i
++) {
race
.
getStages
().
get
(
i
).
go
(
this
);
}
if
(
HW5Lesson
.
FINISH
.
getCount
() ==
// determine the winner
HW5Lesson
.
CARS_COUNT
)
// of the race
System
.
out
.
println
(
name
+
" - WIN"
);
try
{
HW5Lesson
.
FINISH
.
countDown
();
// we expect the finish
HW5Lesson
.
FINISH
.
await
();
// of all racers
}
catch
(
InterruptedException
e
) {
e
.
printStackTrace
();
}
}
}
abstract
class
Stage
{
protected
int
length
;
protected
String
description
;
public
String
getDescription
() {
return
description
;
}
public
abstract
void
go
(
Car
car
);
}
class
Road
extends
Stage
{
public
Road
(
int
length
) {
this
.
length
=
length
;
this
.
description
=
"Road "
+
length
+
" meters"
;
}
@
Override
public
void
go
(
Car
car
) {
try
{
System
.
out
.
println
(
car
.
getName
() +
" started the stage: "
+
description
);
Thread
.
sleep
(
length
/
car
.
getSpeed
() *
1000
);
System
.
out
.
println
(
car
.
getName
() +
" finished the stage: "
+
description
);
}
catch
(
InterruptedException
e
) {
e
.
printStackTrace
();
}
}
}
class
Tunnel
extends
Stage
{
public
Tunnel
() {
this
.
length
=
80
;
this
.
description
=
"Tunnel "
+
length
+
" meters"
;
}
@
Override
public
void
go
(
Car
car
) {
try
{
try
{
System
.
out
.
println
(
car
.
getName
() +
" prepares for the stage (waits): "
+
description
);
HW5Lesson
.
TUNNEL
.
acquire
();
// block the tunnel
System
.
out
.
println
(
car
.
getName
() +
" started the stage: "
+
description
);
Thread
.
sleep
(
length
/
car
.
getSpeed
() *
1000
);
HW5Lesson
.
TUNNEL
.
release
();
// release the tunnel
}
catch
(
InterruptedException
e
) {
e
.
printStackTrace
();
}
finally
{
System
.
out
.
println
(
car
.
getName
() +
" finished the stage: "
+
description
);
}
}
catch
(
Exception
e
) {
e
.
printStackTrace
();
}
}
}
class
Race
{
private
ArrayList
<
Stage
>
stages
;
public
Race
(
Stage
...
stages
) {
this
.
stages
=
new
ArrayList
<>(
Arrays
.
asList
(
stages
));
}
public
ArrayList
<
Stage
>
getStages
() {
return
stages
;
}
}
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