Difference between field and constructor injections in Dagger
Hi I have a very simple dagger questions for android.
class Fooz {
@Inject Foo1 mFoo1;
public Fooz() {
....
}
}
class Fooz {
private Foo1 mFoo1;
@Inject public Fooz(Foo1 foo1) {
mFoo1 = foo1;
}
}
How are the two classes identical?
The first one injects Foo1 field directly while the second one assignes mFoo1 in the constructor.
For the second one, does Foo1 get injected from object graph as soon as Fooz is created and added to object graph?
If they are different, why so?
Thanks!
java
android dagger edited Nov 20 '18 at 17:40
Mikhail Kholodkov
4,85152850
asked Nov 20 '18 at 16:49
user2062024user2062024
1,28652437
add a comment |
Hi I have a very simple dagger questions for android.
class Fooz {
@Inject Foo1 mFoo1;
public Fooz() {
....
}
}
class Fooz {
private Foo1 mFoo1;
@Inject public Fooz(Foo1 foo1) {
mFoo1 = foo1;
}
}
How are the two classes identical?
The first one injects Foo1 field directly while the second one assignes mFoo1 in the constructor.
For the second one, does Foo1 get injected from object graph as soon as Fooz is created and added to object graph?
If they are different, why so?
Thanks!
java
android dagger edited Nov 20 '18 at 17:40
Mikhail Kholodkov
4,85152850
asked Nov 20 '18 at 16:49
user2062024user2062024
1,28652437
Possible duplicate of stackoverflow.com/questions/36078137/…
– Ricardo Costeira
Nov 20 '18 at 17:03
add a comment |
Hi I have a very simple dagger questions for android.
class Fooz {
@Inject Foo1 mFoo1;
public Fooz() {
....
}
}
class Fooz {
private Foo1 mFoo1;
@Inject public Fooz(Foo1 foo1) {
mFoo1 = foo1;
}
}
How are the two classes identical?
The first one injects Foo1 field directly while the second one assignes mFoo1 in the constructor.
For the second one, does Foo1 get injected from object graph as soon as Fooz is created and added to object graph?
If they are different, why so?
Thanks!
java
android dagger edited Nov 20 '18 at 17:40
Mikhail Kholodkov
4,85152850
asked Nov 20 '18 at 16:49
user2062024user2062024
1,28652437
Hi I have a very simple dagger questions for android.
class Fooz {
@Inject Foo1 mFoo1;
public Fooz() {
....
}
}
class Fooz {
private Foo1 mFoo1;
@Inject public Fooz(Foo1 foo1) {
mFoo1 = foo1;
}
}
How are the two classes identical?
The first one injects Foo1 field directly while the second one assignes mFoo1 in the constructor.
For the second one, does Foo1 get injected from object graph as soon as Fooz is created and added to object graph?
If they are different, why so?
Thanks!
java
android dagger java
android dagger edited Nov 20 '18 at 17:40
Mikhail Kholodkov
4,85152850
asked Nov 20 '18 at 16:49
user2062024user2062024
1,28652437
edited Nov 20 '18 at 17:40
Mikhail Kholodkov
4,85152850
asked Nov 20 '18 at 16:49
user2062024user2062024
1,28652437
edited Nov 20 '18 at 17:40
Mikhail Kholodkov
4,85152850
edited Nov 20 '18 at 17:40
Mikhail Kholodkov
4,85152850
edited Nov 20 '18 at 17:40
Mikhail Kholodkov
4,85152850
4,85152850
asked Nov 20 '18 at 16:49
user2062024user2062024
1,28652437
asked Nov 20 '18 at 16:49
user2062024user2062024
1,28652437
asked Nov 20 '18 at 16:49
user2062024user2062024
1,28652437
1,28652437
Possible duplicate of stackoverflow.com/questions/36078137/…
– Ricardo Costeira
Nov 20 '18 at 17:03
add a comment |
Possible duplicate of stackoverflow.com/questions/36078137/…
– Ricardo Costeira
Nov 20 '18 at 17:03
Possible duplicate of stackoverflow.com/questions/36078137/…
– Ricardo Costeira
Nov 20 '18 at 17:03
Possible duplicate of stackoverflow.com/questions/36078137/…
– Ricardo Costeira
Nov 20 '18 at 17:03
add a comment |
2 Answers
2
active
oldest
votes
Constructor injection gives you more control over the object instantiation since using field injections means to restrict your class creation to reflection and rely on support to these particular injection annotations. Besides that, having the dependencies clearly on the constructor let the code easier to maintain and to test.
As far as I know, there is no difference regarding the way it is held on the dagger graph but a constructor call is always faster than injected fields.
In my opinion, we should use property when we do not have control over the object creation, as in Activities and Fragments, per example.
answered Nov 20 '18 at 17:17
haroldolivieriharoldolivieri
329214
add a comment |
These classes will behave the same when Fooz will be Injected using dependency injection. However they will behave differently when constructed using Constructor's you defined.
Example 1. Calling new Fooz() will result in mFoo1 being null.
Example 2. Calling new Fooz(foo1) will result in mFoo1 being initialized to foo1.
The preferred (personal opinion) way is to use dependency injection annotation on constructor, because it will avoid null pointer exceptions, as explained when comparing example 1 and example 2. What is more such constructor gives more flexibility when testing your classes as you can provide mocks, much easier.
These is sonarqube rule with better description, explaining what I mentioned https://sonarcloud.io/coding_rules?open=squid%3AS3306&rule_key=squid%3AS3306 .
answered Nov 20 '18 at 17:14
DonatasDDonatasD
458310
add a comment |
Your Answer
StackExchange.ifUsing("editor", function () {
StackExchange.using("externalEditor", function () {
StackExchange.using("snippets", function () {
StackExchange.snippets.init();
});
});
}, "code-snippets");
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "1"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f53397756%2fdifference-between-field-and-constructor-injections-in-dagger%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
Constructor injection gives you more control over the object instantiation since using field injections means to restrict your class creation to reflection and rely on support to these particular injection annotations. Besides that, having the dependencies clearly on the constructor let the code easier to maintain and to test.
As far as I know, there is no difference regarding the way it is held on the dagger graph but a constructor call is always faster than injected fields.
In my opinion, we should use property when we do not have control over the object creation, as in Activities and Fragments, per example.
answered Nov 20 '18 at 17:17
haroldolivieriharoldolivieri
329214
add a comment |
Constructor injection gives you more control over the object instantiation since using field injections means to restrict your class creation to reflection and rely on support to these particular injection annotations. Besides that, having the dependencies clearly on the constructor let the code easier to maintain and to test.
As far as I know, there is no difference regarding the way it is held on the dagger graph but a constructor call is always faster than injected fields.
In my opinion, we should use property when we do not have control over the object creation, as in Activities and Fragments, per example.
answered Nov 20 '18 at 17:17
haroldolivieriharoldolivieri
329214
add a comment |
Constructor injection gives you more control over the object instantiation since using field injections means to restrict your class creation to reflection and rely on support to these particular injection annotations. Besides that, having the dependencies clearly on the constructor let the code easier to maintain and to test.
As far as I know, there is no difference regarding the way it is held on the dagger graph but a constructor call is always faster than injected fields.
In my opinion, we should use property when we do not have control over the object creation, as in Activities and Fragments, per example.
answered Nov 20 '18 at 17:17
haroldolivieriharoldolivieri
329214
Constructor injection gives you more control over the object instantiation since using field injections means to restrict your class creation to reflection and rely on support to these particular injection annotations. Besides that, having the dependencies clearly on the constructor let the code easier to maintain and to test.
As far as I know, there is no difference regarding the way it is held on the dagger graph but a constructor call is always faster than injected fields.
In my opinion, we should use property when we do not have control over the object creation, as in Activities and Fragments, per example.
answered Nov 20 '18 at 17:17
haroldolivieriharoldolivieri
329214
answered Nov 20 '18 at 17:17
haroldolivieriharoldolivieri
329214
answered Nov 20 '18 at 17:17
haroldolivieriharoldolivieri
329214
answered Nov 20 '18 at 17:17
haroldolivieriharoldolivieri
329214
329214
add a comment |
add a comment |
These classes will behave the same when Fooz will be Injected using dependency injection. However they will behave differently when constructed using Constructor's you defined.
Example 1. Calling new Fooz() will result in mFoo1 being null.
Example 2. Calling new Fooz(foo1) will result in mFoo1 being initialized to foo1.
The preferred (personal opinion) way is to use dependency injection annotation on constructor, because it will avoid null pointer exceptions, as explained when comparing example 1 and example 2. What is more such constructor gives more flexibility when testing your classes as you can provide mocks, much easier.
These is sonarqube rule with better description, explaining what I mentioned https://sonarcloud.io/coding_rules?open=squid%3AS3306&rule_key=squid%3AS3306 .
answered Nov 20 '18 at 17:14
DonatasDDonatasD
458310
add a comment |
These classes will behave the same when Fooz will be Injected using dependency injection. However they will behave differently when constructed using Constructor's you defined.
Example 1. Calling new Fooz() will result in mFoo1 being null.
Example 2. Calling new Fooz(foo1) will result in mFoo1 being initialized to foo1.
The preferred (personal opinion) way is to use dependency injection annotation on constructor, because it will avoid null pointer exceptions, as explained when comparing example 1 and example 2. What is more such constructor gives more flexibility when testing your classes as you can provide mocks, much easier.
These is sonarqube rule with better description, explaining what I mentioned https://sonarcloud.io/coding_rules?open=squid%3AS3306&rule_key=squid%3AS3306 .
answered Nov 20 '18 at 17:14
DonatasDDonatasD
458310
add a comment |
These classes will behave the same when Fooz will be Injected using dependency injection. However they will behave differently when constructed using Constructor's you defined.
Example 1. Calling new Fooz() will result in mFoo1 being null.
Example 2. Calling new Fooz(foo1) will result in mFoo1 being initialized to foo1.
The preferred (personal opinion) way is to use dependency injection annotation on constructor, because it will avoid null pointer exceptions, as explained when comparing example 1 and example 2. What is more such constructor gives more flexibility when testing your classes as you can provide mocks, much easier.
These is sonarqube rule with better description, explaining what I mentioned https://sonarcloud.io/coding_rules?open=squid%3AS3306&rule_key=squid%3AS3306 .
answered Nov 20 '18 at 17:14
DonatasDDonatasD
458310
These classes will behave the same when Fooz will be Injected using dependency injection. However they will behave differently when constructed using Constructor's you defined.
Example 1. Calling new Fooz() will result in mFoo1 being null.
Example 2. Calling new Fooz(foo1) will result in mFoo1 being initialized to foo1.
The preferred (personal opinion) way is to use dependency injection annotation on constructor, because it will avoid null pointer exceptions, as explained when comparing example 1 and example 2. What is more such constructor gives more flexibility when testing your classes as you can provide mocks, much easier.
These is sonarqube rule with better description, explaining what I mentioned https://sonarcloud.io/coding_rules?open=squid%3AS3306&rule_key=squid%3AS3306 .
answered Nov 20 '18 at 17:14
DonatasDDonatasD
458310
answered Nov 20 '18 at 17:14
DonatasDDonatasD
458310
answered Nov 20 '18 at 17:14
DonatasDDonatasD
458310
answered Nov 20 '18 at 17:14
DonatasDDonatasD
458310
458310
add a comment |
add a comment |
Thanks for contributing an answer to Stack Overflow!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f53397756%2fdifference-between-field-and-constructor-injections-in-dagger%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Possible duplicate of stackoverflow.com/questions/36078137/…
– Ricardo Costeira
Nov 20 '18 at 17:03