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Java11/Examples

Revision as of 05:30, 16 August 2018 by Manoj.palat.in.ibm.com (Talk | contribs) (Java 11 Examples)

This is an informal page listing examples of features that are implemented by the Java 11 Support. You are welcome to try out these examples. If you find bugs, please file a bug after checking for a duplicate entry here.


Feature / Steps Expected Result
The Pre-requisite: Java 11 JRE Support
Add Java 11 JRE Use Window -> Preferences-> Java -> Installed JREs -> Add...


FileAddJ11.jpg
[note: Eclipse -> Preferences in Mac / Window -> Preferences in Windows]

Java 11 JRE recognized as a valid JRE
Project JRE In Package Explorer Use project's context menu and add Java 11 JRE JRE specific (eg Object) gets resolved in the project.
Package Explorer Go to Package Explorer and expand the Java 11 JRE Modules (eg java.base etc) are listed in the package explorer view
The First Step: Java 11 Compliance
Set Project Compliance in Package Explorer Context Menu of Project -> Properties -> Set project-specific, drop down to 11



J11.compliance.jpg

11 is shown in the drop down list
Basic Necessity : Compilation and Error Reporting
Positive Compilation Use the following code:
package pack1;
public class VarLambda {
 
	public static void main(String[] args) {
  		I lam = (var  x) -> { // var compiles here
  			System.out.println(x);
  		};
  		lam.apply(20);
	} 
}
 
interface I {
	public void apply(Integer k);
}



Var11.compile.jpg

Code compiles
Compiler Error Case 1
package pack1;
public class VarLambdaErr {
 
	public static void main(String[] args) {
  		I lam = (var  x, z) -> { // should not mix with type-elided params
  			System.out.println(x);
  		};
  		lam.apply(20);
	} 
}
 
interface I {
	public void apply(Integer k, Integer z);
}
Compiler errors are shown
Compiler Error Case 2
package pack1;
public class VarLambdaErr {
 
	public static void main(String[] args) {
  		I lam = (var  x, Integer z) -> { // should not mix with non-var params
  			System.out.println(x);
  		};
  		lam.apply(20, 200);
	} 
}
 
interface I {
	public void apply(Integer k, Integer z);
}

Compiler errors shown

Hover and Navigation
Hover Use the following code:
package pack1;
public class VarLambda {
 
	public static void main(String[] args) {
  		I lam = (var  x) -> { // hover over var
  			System.out.println(x);
  		};
  		lam.apply(20);
	} 
}
 
interface I {
	public void apply(Integer k);
}



Var11.hover.jpg

Hover and Navigation
Nestmates
Basic Nesting Principles
    Description: Nest Based Access - A JVM Concept.
    A top level class and all inner classes form a single unit for access, a "nest".JVM 
    specification added two attributes in the classfile NestHost and NestMember. The top 
    most class will have the NestMember attribute listing all the members while each of 
    the inner classes will have a NestHost attribute listing the top level class. Using 
    this, some of the synthetic bridge methods are elided transparent to the programmer.
    Note that this feature is relevant only for tools that process byte code and hence, 
    in general, this feature would be "transparent" to a "normal" programmer. This feature 
    is applicable for byte code processors, for eg our Disassembler has been enhanced to 
    show these attributes. For further info please read JEP 181.


public class X { 
   private class A {
    class B {}
  }
  private class Y extends A {
  }
}


In X.class (Disassembled)

Nest Members:

  #21 X$A,
  #24 X$A$B,
  #27 X$Y

In each of X$A, X$A$B, X$Y the attribute: Nest Host: #22 X

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