How to avoid nested forEach calls?
up vote
6
down vote
favorite
I have the following code:
interface Device {
// ...
boolean isDisconnected();
void reconnect();
}
interface Gateway {
// ...
List<Device> getDevices();
}
...
for (Gateway gateway : gateways) {
for(Device device : gateway.getDevices()){
if(device.isDisconnected()){
device.reconnect();
}
}
}
I want to refactor the code using Stream API. My first attempt was like the following:
gateways.stream()
.forEach(gateway -> {
gateway.getDevices()
.parallelStream()
.filter(device -> device.isDisconnected())
.forEach(device -> device.reconnect());
}
);
I didn't like it so after some modifications I ended up with this code:
gateways.parallelStream()
.map(gateway -> gateway.getDevices().parallelStream())
.map(stream -> stream.filter(device -> device.isDisconnected()))
.forEach(stream -> stream.forEach(device -> device.reconnect()));
My question is whether there is a way to avoid nested forEach
.
java collections foreach java-8 java-stream
add a comment |
up vote
6
down vote
favorite
I have the following code:
interface Device {
// ...
boolean isDisconnected();
void reconnect();
}
interface Gateway {
// ...
List<Device> getDevices();
}
...
for (Gateway gateway : gateways) {
for(Device device : gateway.getDevices()){
if(device.isDisconnected()){
device.reconnect();
}
}
}
I want to refactor the code using Stream API. My first attempt was like the following:
gateways.stream()
.forEach(gateway -> {
gateway.getDevices()
.parallelStream()
.filter(device -> device.isDisconnected())
.forEach(device -> device.reconnect());
}
);
I didn't like it so after some modifications I ended up with this code:
gateways.parallelStream()
.map(gateway -> gateway.getDevices().parallelStream())
.map(stream -> stream.filter(device -> device.isDisconnected()))
.forEach(stream -> stream.forEach(device -> device.reconnect()));
My question is whether there is a way to avoid nested forEach
.
java collections foreach java-8 java-stream
add a comment |
up vote
6
down vote
favorite
up vote
6
down vote
favorite
I have the following code:
interface Device {
// ...
boolean isDisconnected();
void reconnect();
}
interface Gateway {
// ...
List<Device> getDevices();
}
...
for (Gateway gateway : gateways) {
for(Device device : gateway.getDevices()){
if(device.isDisconnected()){
device.reconnect();
}
}
}
I want to refactor the code using Stream API. My first attempt was like the following:
gateways.stream()
.forEach(gateway -> {
gateway.getDevices()
.parallelStream()
.filter(device -> device.isDisconnected())
.forEach(device -> device.reconnect());
}
);
I didn't like it so after some modifications I ended up with this code:
gateways.parallelStream()
.map(gateway -> gateway.getDevices().parallelStream())
.map(stream -> stream.filter(device -> device.isDisconnected()))
.forEach(stream -> stream.forEach(device -> device.reconnect()));
My question is whether there is a way to avoid nested forEach
.
java collections foreach java-8 java-stream
I have the following code:
interface Device {
// ...
boolean isDisconnected();
void reconnect();
}
interface Gateway {
// ...
List<Device> getDevices();
}
...
for (Gateway gateway : gateways) {
for(Device device : gateway.getDevices()){
if(device.isDisconnected()){
device.reconnect();
}
}
}
I want to refactor the code using Stream API. My first attempt was like the following:
gateways.stream()
.forEach(gateway -> {
gateway.getDevices()
.parallelStream()
.filter(device -> device.isDisconnected())
.forEach(device -> device.reconnect());
}
);
I didn't like it so after some modifications I ended up with this code:
gateways.parallelStream()
.map(gateway -> gateway.getDevices().parallelStream())
.map(stream -> stream.filter(device -> device.isDisconnected()))
.forEach(stream -> stream.forEach(device -> device.reconnect()));
My question is whether there is a way to avoid nested forEach
.
java collections foreach java-8 java-stream
java collections foreach java-8 java-stream
edited 6 hours ago
ETO
1,416218
1,416218
asked 7 hours ago
Hans van Kessels
659
659
add a comment |
add a comment |
3 Answers
3
active
oldest
votes
up vote
5
down vote
accepted
You should flatten the stream of streams using flatMap
instead of map
:
gateways.parallelStream()
.flatMap(gateway -> gateway.getDevices().parallelStream())
.filter(device -> device.isDisconnected())
.forEach(device -> device.reconnect());
I would improve it further by using method references instead of lambda expressions:
gateways.parallelStream()
.map(Gateway::getDevices)
.flatMap(List::stream)
.filter(Device::isDisconnected)
.forEach(Device::reconnect);
Thank you, it works! Does the code withmethod references
have the same performance as the first one? It looks pretty elegant.
– Hans van Kessels
7 hours ago
1
Yes, it does. Please read this post for more detailed explanation.
– ETO
7 hours ago
add a comment |
up vote
5
down vote
Don't refactor your code into using Streams. You gain no benefits and gain no advantages over doing it like this, since the code is now less readable and less idiomatic for future maintainers.
By not using streams, you avoid nested forEach
statements.
Remember: streams are meant to be side-effect free for safer parallelization. forEach
by definition introduces side-effects. You lose the benefit of streams and lose readability at the same time, making this less desirable to do at all.
Thanks for your answer. This is just my in-home project. I'm trying to learn Stream API by doing some pseudo-real tasks.
– Hans van Kessels
7 hours ago
One way to learn about the Stream API is to know when not to apply it. This feels like one of those times, especially since you're not guaranteed that the operations you're performing inside of the stream are side-effect free which would make parallelization safe.
– Makoto
7 hours ago
add a comment |
up vote
2
down vote
I would try this with a sequential stream before using a parallel one:
gateways.stream()
.flatMap(gateway -> gateway.getDevices().stream())
.filter(device -> device.isDisconnected())
.forEach(device -> device.reconnect());
The idea is to create a stream via gateways.stream()
then flatten the sequences returned from gateway.getDevices()
via flatMap
.
Then we apply a filter
operation which acts like the if
statement in your code and finally, a forEach
terminal operation enabling us to invoke reconnect
on each and every device passing the filter operation.
see Should I always use a parallel stream when possible?
add a comment |
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3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
5
down vote
accepted
You should flatten the stream of streams using flatMap
instead of map
:
gateways.parallelStream()
.flatMap(gateway -> gateway.getDevices().parallelStream())
.filter(device -> device.isDisconnected())
.forEach(device -> device.reconnect());
I would improve it further by using method references instead of lambda expressions:
gateways.parallelStream()
.map(Gateway::getDevices)
.flatMap(List::stream)
.filter(Device::isDisconnected)
.forEach(Device::reconnect);
Thank you, it works! Does the code withmethod references
have the same performance as the first one? It looks pretty elegant.
– Hans van Kessels
7 hours ago
1
Yes, it does. Please read this post for more detailed explanation.
– ETO
7 hours ago
add a comment |
up vote
5
down vote
accepted
You should flatten the stream of streams using flatMap
instead of map
:
gateways.parallelStream()
.flatMap(gateway -> gateway.getDevices().parallelStream())
.filter(device -> device.isDisconnected())
.forEach(device -> device.reconnect());
I would improve it further by using method references instead of lambda expressions:
gateways.parallelStream()
.map(Gateway::getDevices)
.flatMap(List::stream)
.filter(Device::isDisconnected)
.forEach(Device::reconnect);
Thank you, it works! Does the code withmethod references
have the same performance as the first one? It looks pretty elegant.
– Hans van Kessels
7 hours ago
1
Yes, it does. Please read this post for more detailed explanation.
– ETO
7 hours ago
add a comment |
up vote
5
down vote
accepted
up vote
5
down vote
accepted
You should flatten the stream of streams using flatMap
instead of map
:
gateways.parallelStream()
.flatMap(gateway -> gateway.getDevices().parallelStream())
.filter(device -> device.isDisconnected())
.forEach(device -> device.reconnect());
I would improve it further by using method references instead of lambda expressions:
gateways.parallelStream()
.map(Gateway::getDevices)
.flatMap(List::stream)
.filter(Device::isDisconnected)
.forEach(Device::reconnect);
You should flatten the stream of streams using flatMap
instead of map
:
gateways.parallelStream()
.flatMap(gateway -> gateway.getDevices().parallelStream())
.filter(device -> device.isDisconnected())
.forEach(device -> device.reconnect());
I would improve it further by using method references instead of lambda expressions:
gateways.parallelStream()
.map(Gateway::getDevices)
.flatMap(List::stream)
.filter(Device::isDisconnected)
.forEach(Device::reconnect);
answered 7 hours ago
ETO
1,416218
1,416218
Thank you, it works! Does the code withmethod references
have the same performance as the first one? It looks pretty elegant.
– Hans van Kessels
7 hours ago
1
Yes, it does. Please read this post for more detailed explanation.
– ETO
7 hours ago
add a comment |
Thank you, it works! Does the code withmethod references
have the same performance as the first one? It looks pretty elegant.
– Hans van Kessels
7 hours ago
1
Yes, it does. Please read this post for more detailed explanation.
– ETO
7 hours ago
Thank you, it works! Does the code with
method references
have the same performance as the first one? It looks pretty elegant.– Hans van Kessels
7 hours ago
Thank you, it works! Does the code with
method references
have the same performance as the first one? It looks pretty elegant.– Hans van Kessels
7 hours ago
1
1
Yes, it does. Please read this post for more detailed explanation.
– ETO
7 hours ago
Yes, it does. Please read this post for more detailed explanation.
– ETO
7 hours ago
add a comment |
up vote
5
down vote
Don't refactor your code into using Streams. You gain no benefits and gain no advantages over doing it like this, since the code is now less readable and less idiomatic for future maintainers.
By not using streams, you avoid nested forEach
statements.
Remember: streams are meant to be side-effect free for safer parallelization. forEach
by definition introduces side-effects. You lose the benefit of streams and lose readability at the same time, making this less desirable to do at all.
Thanks for your answer. This is just my in-home project. I'm trying to learn Stream API by doing some pseudo-real tasks.
– Hans van Kessels
7 hours ago
One way to learn about the Stream API is to know when not to apply it. This feels like one of those times, especially since you're not guaranteed that the operations you're performing inside of the stream are side-effect free which would make parallelization safe.
– Makoto
7 hours ago
add a comment |
up vote
5
down vote
Don't refactor your code into using Streams. You gain no benefits and gain no advantages over doing it like this, since the code is now less readable and less idiomatic for future maintainers.
By not using streams, you avoid nested forEach
statements.
Remember: streams are meant to be side-effect free for safer parallelization. forEach
by definition introduces side-effects. You lose the benefit of streams and lose readability at the same time, making this less desirable to do at all.
Thanks for your answer. This is just my in-home project. I'm trying to learn Stream API by doing some pseudo-real tasks.
– Hans van Kessels
7 hours ago
One way to learn about the Stream API is to know when not to apply it. This feels like one of those times, especially since you're not guaranteed that the operations you're performing inside of the stream are side-effect free which would make parallelization safe.
– Makoto
7 hours ago
add a comment |
up vote
5
down vote
up vote
5
down vote
Don't refactor your code into using Streams. You gain no benefits and gain no advantages over doing it like this, since the code is now less readable and less idiomatic for future maintainers.
By not using streams, you avoid nested forEach
statements.
Remember: streams are meant to be side-effect free for safer parallelization. forEach
by definition introduces side-effects. You lose the benefit of streams and lose readability at the same time, making this less desirable to do at all.
Don't refactor your code into using Streams. You gain no benefits and gain no advantages over doing it like this, since the code is now less readable and less idiomatic for future maintainers.
By not using streams, you avoid nested forEach
statements.
Remember: streams are meant to be side-effect free for safer parallelization. forEach
by definition introduces side-effects. You lose the benefit of streams and lose readability at the same time, making this less desirable to do at all.
edited 7 hours ago
answered 7 hours ago
Makoto
80.2k15125170
80.2k15125170
Thanks for your answer. This is just my in-home project. I'm trying to learn Stream API by doing some pseudo-real tasks.
– Hans van Kessels
7 hours ago
One way to learn about the Stream API is to know when not to apply it. This feels like one of those times, especially since you're not guaranteed that the operations you're performing inside of the stream are side-effect free which would make parallelization safe.
– Makoto
7 hours ago
add a comment |
Thanks for your answer. This is just my in-home project. I'm trying to learn Stream API by doing some pseudo-real tasks.
– Hans van Kessels
7 hours ago
One way to learn about the Stream API is to know when not to apply it. This feels like one of those times, especially since you're not guaranteed that the operations you're performing inside of the stream are side-effect free which would make parallelization safe.
– Makoto
7 hours ago
Thanks for your answer. This is just my in-home project. I'm trying to learn Stream API by doing some pseudo-real tasks.
– Hans van Kessels
7 hours ago
Thanks for your answer. This is just my in-home project. I'm trying to learn Stream API by doing some pseudo-real tasks.
– Hans van Kessels
7 hours ago
One way to learn about the Stream API is to know when not to apply it. This feels like one of those times, especially since you're not guaranteed that the operations you're performing inside of the stream are side-effect free which would make parallelization safe.
– Makoto
7 hours ago
One way to learn about the Stream API is to know when not to apply it. This feels like one of those times, especially since you're not guaranteed that the operations you're performing inside of the stream are side-effect free which would make parallelization safe.
– Makoto
7 hours ago
add a comment |
up vote
2
down vote
I would try this with a sequential stream before using a parallel one:
gateways.stream()
.flatMap(gateway -> gateway.getDevices().stream())
.filter(device -> device.isDisconnected())
.forEach(device -> device.reconnect());
The idea is to create a stream via gateways.stream()
then flatten the sequences returned from gateway.getDevices()
via flatMap
.
Then we apply a filter
operation which acts like the if
statement in your code and finally, a forEach
terminal operation enabling us to invoke reconnect
on each and every device passing the filter operation.
see Should I always use a parallel stream when possible?
add a comment |
up vote
2
down vote
I would try this with a sequential stream before using a parallel one:
gateways.stream()
.flatMap(gateway -> gateway.getDevices().stream())
.filter(device -> device.isDisconnected())
.forEach(device -> device.reconnect());
The idea is to create a stream via gateways.stream()
then flatten the sequences returned from gateway.getDevices()
via flatMap
.
Then we apply a filter
operation which acts like the if
statement in your code and finally, a forEach
terminal operation enabling us to invoke reconnect
on each and every device passing the filter operation.
see Should I always use a parallel stream when possible?
add a comment |
up vote
2
down vote
up vote
2
down vote
I would try this with a sequential stream before using a parallel one:
gateways.stream()
.flatMap(gateway -> gateway.getDevices().stream())
.filter(device -> device.isDisconnected())
.forEach(device -> device.reconnect());
The idea is to create a stream via gateways.stream()
then flatten the sequences returned from gateway.getDevices()
via flatMap
.
Then we apply a filter
operation which acts like the if
statement in your code and finally, a forEach
terminal operation enabling us to invoke reconnect
on each and every device passing the filter operation.
see Should I always use a parallel stream when possible?
I would try this with a sequential stream before using a parallel one:
gateways.stream()
.flatMap(gateway -> gateway.getDevices().stream())
.filter(device -> device.isDisconnected())
.forEach(device -> device.reconnect());
The idea is to create a stream via gateways.stream()
then flatten the sequences returned from gateway.getDevices()
via flatMap
.
Then we apply a filter
operation which acts like the if
statement in your code and finally, a forEach
terminal operation enabling us to invoke reconnect
on each and every device passing the filter operation.
see Should I always use a parallel stream when possible?
answered 7 hours ago
Aomine
36.6k72961
36.6k72961
add a comment |
add a comment |
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