Skip to main content

Java closure shows his face - Lambda expression

JSR335, Lambda expression started review ballot stage on November 16th 2010. Java closure finally show the new breath taking expression. Citing from the detail of JSR request:

...
2.7 Please give a short description of the underlying technology or technologies:

We propose extending the Java Language to support compact lambda expressions (otherwise known as closures or anonymous methods.) Additionally, we will extend the language to support a conversion known as "SAM conversion" to allow lambda expressions to be used where a single-abstract-method interface or class is expected, enabling forward compatibility of existing libraries.

We propose extending the semantics of interfaces in the Java Language to support virtual extension methods, whereby an interface can nominate a static default method to stand in for the implementation of an interface method in the event that an implementation class does not provide an implementation of the extension method. This enables interfaces to be augmented with new methods "after the fact" without breaking existing implementation classes.

Time permitting, we will use these features to augment the core Java SE libraries to support a more lambda-friendly style of programming, such as:
Collection collection = ... ;
collection.sortBy(#{ Foo f -> f.getLastName() });
or

collection.remove(#{ Foo f -> f.isBlue() });
This will likely be accompanied by a set of standardized "SAM" types such as Predicate, Filter, Mapper, Reducer, etc.
...

Comments

Popular posts from this blog

Publish Maven site with Amazon S3 and CloudFront

Amazon S3 now supports static website hosting . As a 10 years Maven user, I wonder how easy it is to deploy Maven generated site to Amazon S3 and let the rock-solid storage provider to host my project websites. There are several existing s3 wagon providers , which all seem to have the same problem, not supporting directory copy. This is understandable since before S3 new website hosting feature, I guess people mostly expect to deploy artifacts rather than website to S3. So my first task is to write an AWS S3 wagon that supports directory copy. With AWS Java SDK , task becomes as simple as one single class . I made my S3 wagon available in Maven central repository at org.cyclopsgroup:awss3-maven-wagon:0.1 . The source code is hosted in github:jiaqi/cym2/awss3 . The next thing is to create an S3 bucket in console . To avoid trouble, bucket name is set to the future website domain name according to this discussion . Website feature needs to be explicitly enabled. I also created an...

Customize IdGenerator in JPA, gap between Hibernate and JPA annotations

JPA annotation is like a subset of Hibernate annotation, this means people will find something available in Hibernate missing in JPA. One of the important missing features in JPA is customized ID generator. JPA doesn't provide an approach for developer to plug in their own IdGenerator. For example, if you want the primary key of a table to be BigInteger coming from sequence, JPA will be out of solution. Assume you don't mind the mixture of Hibernate and JPA Annotation and your JPA provider is Hibernate, which is mostly the case, a solution before JPA starts introducing new Annotation is, to replace JPA @SequenceGenerator with Hibernate @GenericGenerator. Now, let the code talk. /** * Ordinary JPA sequence. * If the Long is changed into BigInteger, * there will be runtime error complaining about the type of primary key */ @Id @Column(name = "id", precision = 12) @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "XyzIdGenerator") @SequenceGe...

Spring, Angular and other reasons I like and hate Bazel at the same time

For several weeks I've been trying to put together an Angular application served Java Spring MVC web server in Bazel. I've seen the Java, Angular combination works well in Google, and given the popularity of Java, I want get it to work with open source. How hard can it be to run arguably the best JS framework on a server in probably the most popular server-side language with  the mono-repo of planet-scale ? The rest of this post walks through the headaches and nightmares I had to get things to work but if you are just here to look for a working example, github/jiaqi/angular-on-java is all you need. https://github.com/jiaqi/angular-on-java Java web application with Appengine rule Surprisingly there isn't an official way of building Java web application in Bazel, the closest thing is the Appengine rule  and Spring MVC seems to work well with it. 3 Java classes, a JSP and an appengine.xml was all I need. At this point, the server starts well but I got "No ...