Is there a good way to access the import declarations of an IType, without manually searching through the source code one can get as a String with getSource()?
Example:
If the IType is this Java class in a source file:
import java.util.Arrays;
import java.util.HashSet;
import java.util.LinkedList;
public class MyClass {
// some content
}
I want to retrieve [java.util.Arrays, java.util.HashSet, java.util.LinkedList]. Whether the imported types are retrieved as Strings or ITypes or something else is not really important for me.
Of the various models of JDT, the Java Model (of which IType is a part) is the most light-weight one. As a consequence it doesn't have the information you are seeking. Only the AST has this information, available as CompilationUnit.imports().
For an introduction to JDT's AST see, e.g., the tutorial slides "How To Train the JDT Dragon" (Slide 31ff).
At a first glance for the task at hand getting the full AST may appear to be overkill, but at least it correctly handles (skips) all comments that might come before / between imports.
Related
Does Java support grouping the imports like following:
import package.{Class1,Class2}
I know that * operator imports sub packages but I want to import specific ones.
In Rust or some modern languages it is supported like following:
use package::{Class1, Class2};
Are there any alternative instead of writing each import line by line specifically like this?
import package.Class1;
import package.Class2;
Java Language Specification, section 7.5. Import Declarations, shows:
An import declaration allows a named type or a static member to be referred to by a simple name (§6.2) that consists of a single identifier.
[...]
A single-type-import declaration (§7.5.1) imports a single named type, by mentioning its canonical name (§6.7).
A type-import-on-demand declaration (§7.5.2) imports all the accessible types of a named type or named package as needed, by mentioning the canonical name of a type or package.
A single-static-import declaration (§7.5.3) imports all accessible static members with a given name from a type, by giving its canonical name.
A static-import-on-demand declaration (§7.5.4) imports all accessible static members of a named type as needed, by mentioning the canonical name of a type.
As you can see, it's either a single named type, or all accessible types. No syntax for a list of types.
Side note: I almost never look at the import statements of my code. I let Eclipse manage that for me (Source > Organize Imports... (Ctrl+Shift+O)), so I don't really care about having many single-type import statements. The section with the imports is collapsed anyway, so I don't even have to scroll past them. Oh the joy of using a good IDE.
In java, only supported ways to import multiple classes are as follows :
A - import individual classes
import package.Class1;
import package.Class2;
B - import all classes in a package or subpackage
import package.*;
import package.subpackage.*;
Refer Oracle doc for more information : https://docs.oracle.com/javase/tutorial/java/package/usepkgs.html
No. Java doesn't have a construct to import a set of select classes using one statement. You either import all types from the package, or you import them one by one.
Using * lets you import all classes from the same package (not to import sub-packages, as you mentioned):
import package.*; //Both Class1 and Class2 are imported
import static package.Class1.* //All static members of Class1 are imported
The first form import package.* is usually discouraged because of the increased potential for name clashes (same class names from different packages). This is probably where import package.{Class1,Class2} would have helped, but there's no such construct in Java.
This question already has answers here:
Meaning of the import statement in a Java file
(5 answers)
Closed 6 years ago.
What does java.util.*; do? Why do we include it at the beginning of our files?
The statement java.util.*; imports all of the java.util package members so that you don't have to use a package member's fully qualified name. According to the JavaDocs here the package java.util
Contains the collections framework, legacy collection classes, event
model, date and time facilities, internationalization, and
miscellaneous utility classes (a string tokenizer, a random-number
generator, and a bit array)
Although this approach can seem more convenient and is sometimes appropriate you shouldn't always be including an import java.util.*; statement at the beginning of all of your files unless you are using a substantial amount of the members contained in the java.util package. Only include the members that you use like so:
import java.util.ArrayList;
import java.util.LinkedList;
By doing so it helps make you more familiar with each package member that you're using instead of blindly importing the whole package. The most important reason is that by using the wildcard character(*) you have a greater chance of coming across name ambiguities which can lead to errors.
import java.awt.*;
import java.util.*;
In the above code example, the class List becomes ambiguous because both packages have a List class.
Think of it like a library of methods that you now have access to. You are basically importing more functionality into your project
When you do
import java.util.*
you now have the ability to do things like create arrays, manipulate dates and so on... (https://docs.oracle.com/javase/7/docs/api/java/util/package-summary.html)
The .* means you are importing all of the util functions like java.util.Arrays or java.util.Date...
When you declare an import like this:
import com.microsoft.azure.storage.*;
Does that include everything in its subpackages too? For example, does it include this?
import com.microsoft.azure.storage.blob.*
If not, why not? (Edit: the "why" question is basically off topic. ignoring that bit when considering a correct answer.)
No it does not. It only imports everything in the package (i.e. the directory itself). Sub-directories are considered to be different packages, so you would need to:
import com.microsoft.azure.storage.*
import com.microsoft.azure.storage.blob.*
As to why the language designers chose to go this route, one can only guess, but the system that they decided to go with does allow for a more fine-grained approach.
yes you can import all the classes from an import but it does not make it possible to import multiple packages with similar names. For example import java.util*; does not also import java.util.prefs or .jar you have to import these all separately. I don't know if that answers your question, and to the why I am not really sure it just makes sense to do it this way. If you were to import similar packages that had the same static variables, but you only need two or three of the packages then you would get errors or code that does not run properly.
There's a name for these - type import on demand.
A type-import-on-demand declaration allows all accessible types of a named package or type to be imported as needed.
They're only also importing the package itself, and not any subpackages, as clarified by the example, emphasis mine:
import java.util.*;
causes the simple names of all public types declared in the package java.util to be available within the class and interface declarations of the compilation unit. Thus, the simple name Vector refers to the type Vector in the package java.util in all places in the compilation unit where that type declaration is not shadowed (§6.4.1) or obscured (§6.4.2).
does that include everything in / subdirectories too? including
something like this?
* stands for all the compilation units inside the package com.microsoft.azure.storage where sub packages are actually not compilation units and thus not fetched when you write myPack.*. Compilation unit includes class, interface, enum etc.
I can't understand why I'm getting the following error - cannot find symbol - class Line2D - when I try to compile this code:
import java.awt.*;
public class KochSegment
{
public Line2D base = new Line2D(); public Line2D[] Lines = new Line2D[4]; //error is on this line
etc.
}
It's in a subpackage:
java.awt.geom.Line2D
So you'd need either
import java.awt.geom.Line2D;
or
import java.awt.geom.*;
Some lessons that should be learned from this:
Star imports only import classes from a package. They do not import from sub-packages as well. In fact, sub-packages in Java are purely syntactic. As far as the Java language is concerned, there is NO semantic relationship between classes in different packages or sub-packages.
Star imports tend to obscure problems. A lot of people recommend not using them. Write the imports out in full. Or better still, use an IDE that can do classname completion, and generate missing imports. (Granted, you do need to be a bit careful when for example the IDE offers you multiple completions for (say) Date or List.)
Searching and reading the javadoc is a good way to help with problems like this. A javadoc search (or a class list scan) would tell you what the fully qualified name for the Line2D class is.
I don't like the fact that in scala its not obvious what some of my imports are doing - imports for implicits so i'm trying to come up with good naming conventions for them so when i see in my import statements something like:
import com.mycomp.example.RectangleImplicits
or
import com.mycomp.example.RectanglePimper
I know i cant remove that import because its being used for pimping.
My problem with the above names is that sometimes I actually do an adapter, in that case
import com.mycomp.example.RectangleAdapter
does not say anyting about the fact that its actually a pimper however i don't want to name it RectangleAdapterPimp because the name becomes to combersome...
is there a golden bullet naming convention for that?
thanks
In std Scala library such classes are prefixed with Rich, like RichString, RichInt, etc... So why not to use RichRectangleAdapter