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Difference between revisions of "Java9/Examples"
< Java9
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− | This is an informal page listing | + | This is an informal page listing examples of features that are implemented by the Java 9 Support for Oxygen. You are welcome to try out these examples. If you find bugs, please file a bug after checking for a duplicate entry [https://bugs.eclipse.org/bugs/buglist.cgi?bug_status=UNCONFIRMED&bug_status=NEW&bug_status=ASSIGNED&bug_status=REOPENED&classification=Eclipse&component=APT&component=Core&component=Debug&component=UI&known_name=J9.Open&list_id=16496392&product=JDT&query_based_on=J9.Open&query_format=advanced&target_milestone=BETA%20J9 here]. |
{| class="wikitable" | {| class="wikitable" | ||
− | + | ||
− | ! scope="row" style="width: 15%;" | | + | ! scope="row" style="width: 15%;" | |
− | + | | style="width: 60%; text-align: center" | '''Feature''' / Steps | |
! style="width: 25%;" | Expected Result | ! style="width: 25%;" | Expected Result | ||
|- | |- | ||
− | ! colspan="3" | Java 9 JRE Support | + | ! colspan="3" | The Pre-requisite: Java 9 JRE Support |
|- | |- | ||
− | ! scope="row" | Add Java 9 | + | ! scope="row" | Add Java 9 JRE |
− | | Use Eclipse Preferences -> Java -> Installed JREs -> Add | + | | Use Eclipse Preferences -> Java -> Installed JREs -> Add <br> |
+ | [[File:Addj9.jpg]] | ||
+ | | Java 9 JRE recognized as a valid JRE | ||
|- | |- | ||
! scope="row" | Project JRE | ! scope="row" | Project JRE | ||
− | | Use Project Context Menu and add Java 9 JRE || JRE specific (eg Object) gets resolved in the project. | + | | In Package Explorer Use Project Context Menu and add Java 9 JRE || JRE specific (eg Object) gets resolved in the project. |
|- | |- | ||
! scope="row" | Package Explorer | ! scope="row" | Package Explorer | ||
− | | Go to Package Explorer and expand the Java 9 JRE || Modules (eg java.base etc) are listed in the | + | | Go to Package Explorer and expand the Java 9 JRE || Modules (eg java.base etc) are listed in the package explorer view |
|- | |- | ||
− | ! colspan="3" | Module Creation | + | ! colspan="3" | The First Step: Module Creation |
|- | |- | ||
! scope="row" | Manual | ! scope="row" | Manual | ||
Line 25: | Line 27: | ||
|- | |- | ||
! scope="row" | Automatic | ! scope="row" | Automatic | ||
− | | Context Menu of Project -> Cofigure -> Create module-info. | + | | Context Menu of Project -> Cofigure -> Create module-info. |
+ | <br> | ||
+ | <br> | ||
+ | [[File:AutomoduleCreate.jpg]] | ||
+ | | A default module-info.java with all packages exported should be created | ||
+ | |- | ||
+ | ! colspan="3" | Basic Necessity : Compilation, Module Dependency & Error Reporting | ||
+ | |- | ||
+ | ! scope="row" | Unspecified Dependency | ||
+ | | create projects "first" and "second" and create module-info.java files in each of giving the module names "first" and "second" respectively. <br> | ||
+ | In the first module add the directive <code> requires second; </code>. This initial configuration would look something similar to the one shown in the figure. | ||
+ | <br> | ||
+ | <br> | ||
+ | [[File:Initmods.jpg]] | ||
+ | | Compiler gives error "second cannot be resolved to a module" | ||
+ | |- | ||
+ | ! scope="row" | Define Dependency | ||
+ | | In the above scenario, add Project second as a dependent project for project first | ||
+ | | Compiler error goes away | ||
+ | |- | ||
+ | ! scope="row" | Duplicate Dependency | ||
+ | | Continuing from the above scenario, add a duplicate <code> requires second;</code> directive in the module-info.java file of the first | ||
+ | | Compiler gives error "Duplicate requires entry: second" | ||
+ | |- | ||
+ | ! scope="row" | Circular Dependency | ||
+ | | add a circular dependency ie | ||
+ | add second project dependent on first <br> | ||
+ | add <code> requires first;</code> directive in the module-info.java file of the second project ie replace <code>// empty by design</code> comment by this directive | ||
+ | | Two compiler errors " Cycle exists in module dependencies, Module second requires itself via first" | ||
+ | |- | ||
+ | ! colspan="3" | Editing with Ease: Completion in module-info.java file | ||
+ | |- | ||
+ | ! scope="row" | Keyword Completion (1) | ||
+ | | In the module-info.java file of say second project, after <code> module first {</code>, press completion key (for eg, ctrl+space in windows) | ||
+ | <br> | ||
+ | <br> | ||
+ | [[File:Keycomplete1.jpg]] | ||
+ | | keywords <code>exports</code>, <code>opens</code>, <code>requires</code>, <code>provides</code> and <code>uses</code> shown | ||
+ | |- | ||
+ | ! scope="row" | Keyword Completion (2) | ||
+ | | after <code>exports packagename</code>, or <code>opens packagename</code> press completion key | ||
+ | | keyword to is shown as an option | ||
+ | |- | ||
+ | ! scope="row" | Package Completion | ||
+ | | after <code>exports</code>, <code>opens</code>, <code>provides</code> or <code>uses</code>, press completion key | ||
+ | | package completion shown. | ||
+ | |- | ||
+ | ! scope="row" | Type Reference Completion | ||
+ | | after <code>exports</code>, <code>opens</code>, <code>provides</code> or <code>uses</code>, or optionally after a dot after a package, ie <code>exports packagename.</code> press completion key | ||
+ | | Type completion shown. | ||
+ | |- | ||
+ | ! scope="row" | Implementation TypeRef Completion | ||
+ | | after <code>provides typename with</code> press completion key | ||
+ | | Type completion shown and these typereferences are implementations of the type given before with. | ||
+ | |- | ||
+ | ! colspan="3" | The Essential Utilities: Code Select, Hover, Navigate, Search and Rename | ||
+ | |- | ||
+ | ! scope="row" | Module Select & Hover | ||
+ | | <br> | ||
+ | In the module-info.java file of the first project, select <code>second</code> in the <code>requires second;</code> directive | ||
+ | <br> | ||
+ | <br> | ||
+ | [[File:Hover.jpg]] | ||
+ | | Hover appears | ||
+ | |- | ||
+ | ! scope="row" | Module Select, Hover & Navigate | ||
+ | | In the above scenario, after hover appears, click on the navigate | ||
+ | | module-info.java file of second opened | ||
+ | |- | ||
+ | ! scope="row" | Module Select, & Search | ||
+ | | <br> | ||
+ | In the module-info.java file of the second project, select second in module declaration <code> module second {</code> and search for references | ||
+ | <br> | ||
+ | <br> | ||
+ | [[File:Modsearch2.jpg]] | ||
+ | | In the search view, the reference in directive <code>requires second;</code> in file first -> module-info.java is shown. | ||
+ | |- | ||
+ | ! scope="row" | Package Search | ||
+ | | <br> | ||
+ | create package <code>pack1</code> to the project first. | ||
+ | <br>add <code>exports pack1;</code> directive in module-info.java file of first. | ||
+ | <br>search for references of <code>pack1</code> | ||
+ | | In the search view, the reference of <code>pack1</code> in directive <code>exports pack1;</code> in file first -> module-info.java is shown, similar to other <code>pack1</code> references if any | ||
+ | |- | ||
+ | ! scope="row" | Type Search | ||
+ | | create Type <code>X</code> in the project first, add directive <code>uses X;</code> in module-info.java file of first, and search for references of X | ||
+ | | In the search view, the reference of <code>X</code> in directive <code>uses X;</code> in file first -> module-info.java is shown, similar to other <code>X</code> references if any | ||
+ | |- | ||
+ | ! scope="row" |Code Select & Rename | ||
+ | | in module-info.java file of first, select <code>X</code> in directive <code>uses X;</code> and rename to <code>X11</code> | ||
+ | | rename exhibits usual behavior - renames definition and references of <code>X</code> to <code>X11</code> | ||
+ | |- | ||
+ | ! colspan="3" | The Outlier: Milling Project Coin Enhancements | ||
+ | |- | ||
+ | ! scope="row" | @Safevarargs | ||
+ | | <code>@SafeVarargs</code> is now allowed on private instance methods. There is even a support of quick assist for that. Use the following code which has warnings, and use the quick assist at the point mentioned in the comment | ||
+ | |||
+ | |||
+ | <source lang="java"> | ||
+ | package packsafe; | ||
+ | import java.util.ArrayList; | ||
+ | import java.util.List; | ||
+ | |||
+ | public class SafeVar { | ||
+ | private int getLen(List<String>...list) { | ||
+ | List<String>[] l = list; | ||
+ | return l.length; | ||
+ | } | ||
+ | |||
+ | public static void main(String[] args) { | ||
+ | SafeVar x = new SafeVar(); | ||
+ | List<String> l = new ArrayList<>(); | ||
+ | int len = x.getLen(l); // Use Quick Assist of SafeVarargs here<br> | ||
+ | System.out.println("Length:" + len); | ||
+ | } | ||
+ | }</source> | ||
+ | | <code>@SafeVarargs</code> inserted before <code>getLen()</code> and the warnings go away | ||
+ | |- | ||
+ | ! scope="row" | Effectively Final AutoCloseables | ||
+ | | Effectively-final variables are allowed to be used as resources in the try-with-resources statement. The code below has an error. Try removing the line <code> t1 = null; // Remove this code </code>. | ||
+ | |||
+ | |||
+ | <source lang="java">package packtry; | ||
+ | import java.io.Closeable; | ||
+ | import java.io.IOException; | ||
+ | |||
+ | class Two implements Closeable { | ||
+ | @Override | ||
+ | public void close() throws IOException { | ||
+ | // nothing | ||
+ | } | ||
+ | } | ||
+ | public class TryStmtTwo { | ||
+ | |||
+ | public void foo() throws IOException { | ||
+ | Two t1 = new Two(); | ||
+ | try (t1; final Two t2 = new Two()) { | ||
+ | // Empty by design | ||
+ | } | ||
+ | t1 = null; // Remove this code | ||
+ | } | ||
+ | public static void main(String[] args) { | ||
+ | System.out.println("Done"); | ||
+ | } | ||
+ | } | ||
+ | </source> | ||
+ | | Code without errors. For the more inquisitive, check the generated code to see that the close is generated for <code>t1</code> as well which is not a final variable but an effectively final variable. | ||
+ | |- | ||
+ | ! scope="row" | Anonymous Diamond | ||
+ | | In the following code, there is a warning about Y being a raw type and need to be parameterized. with Java 9 support, just add a diamond operator after Y. | ||
+ | |||
+ | |||
+ | <source lang="java"> | ||
+ | public class Dia { | ||
+ | @SuppressWarnings("unused") | ||
+ | public static void main(String[] args) { | ||
+ | Y<?> y1 = new Y(){}; // Change this to new Y<>(){} | ||
+ | } | ||
+ | } | ||
+ | class Y<T> {} | ||
+ | </source> | ||
+ | |||
+ | | Diamond operator <code><></code> accepted and code compiles without warning | ||
+ | |- | ||
+ | ! scope="row" | Illegal Underscore | ||
+ | | Underscore is an illegal identifier from Java 9 onwards. Uncomment the commented line in the following example | ||
+ | |||
+ | |||
+ | <source lang="java">public class UnderScore { | ||
+ | //Integer _ ; | ||
+ | } | ||
+ | </source> | ||
+ | | error: "'_' should not be used as an identifier, since it is a reserved keyword from source level 1.8 on" | ||
+ | |- | ||
+ | ! scope="row" | Private Methods | ||
+ | | private interface methods are allowed. Change the <code>default</code> of worker to private | ||
+ | |||
+ | |||
+ | <source lang="java"> | ||
+ | public interface I { | ||
+ | default void worker() {}< | ||
+ | |||
+ | default void foo() { | ||
+ | worker(); | ||
+ | } | ||
+ | |||
+ | default void bar() { | ||
+ | worker(); | ||
+ | } | ||
+ | } | ||
+ | </source> | ||
+ | | Code compiles with <code>private</code> as well. Note that this is a useful feature if two default methods wants to share the worker code and does not want the worker to be an public interface method. | ||
+ | |- | ||
+ | ! colspan="3" | Coming Soon to an Eclipse Version nearby you: The Java 9 DOM AST for module, Automatic Modules support, Quick Fixes and more...Watch this space for updates. | ||
|} | |} |
Latest revision as of 10:04, 4 June 2018
This is an informal page listing examples of features that are implemented by the Java 9 Support for Oxygen. You are welcome to try out these examples. If you find bugs, please file a bug after checking for a duplicate entry here.