java类中的导入顺序是什么以及如何解决它

Question

In my java class there are multiple imports are there like showen below.

import java.util.ArrayList;
import java.util.Date;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

my question is sonar report is telling minor violation under category of Import Order .

Wrong order for 'java.util.ArrayList' import.

what exactly it means and how to resolve this sonar violations.

Thanks in advance.

Answer 1

There is nothing wrong with the import java.util.ArrayList in isolation—it just happens to be the first one that breaks the rule. The full answer to your question will require all of your imports to be shown. The most probable cause is import group ordering.

Answer 2

As I've learned from my experience, classes within one package must be sorted alphabetically. So look at classes located before ArrayList and refer to java.util package, if they are any. In my case it was to be as follows:

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Date;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

Answer 3

I know I'm late to the party here but this could help others.

import java.util.ArrayList;
import java.util.Date;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

The above does not break the rule as it is well sorted alphabetically, you get the "Wrong order for 'java.util.' import." when any of these imports are in between other imports without the proper sort order. For instance:

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.util.ArrayList;
import java.util.Date;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

The above break the rule as the imports are not well sorted. To fix this, just move the "java.util" imports above the "org.slf4j" imports. Kind of like:

import java.util.ArrayList;
import java.util.Date;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

Also, there seems to be an order to how imports should be arranged apart from alphabetical sorting.

1. Static imports
2. imports from other packages in the same project
3. Imports from java
4. Imports from the framework
5. All other imports

Answer 4

If you are using eclipse then try Ctrl+Shift+O to fix imports.

Also see this question .

Answer 5

The order of the import statements does not matter to the compiler or JVM. It's just a coding style preference. Personally, I like to use import some.package.* if I am using more than 3 classes for a particular package.

Answer 6

将 ArrayList 导入放在 List 导入之后。