The Object Teams Blog

Adding team spirit to your objects.

Compiling OT/Equinox projects using Tycho

with 3 comments

In a previous post I showed how the tycho-compiler-jdt Maven plug-in can be used for compiling OT/J code with Maven.

Recently, I was asked how the same can be done for OT/Equinox projects. Given that we were already using parts from Tycho, this shouldn’t be so difficult, right?

Once you know the solution, finding the solution is indeed easy, also in this case. Here it is:

We use almost the same declaration as for plain OT/J applications:

    <pluginManagement>
	<plugin>
	    <groupId>org.eclipse.tycho</groupId>
	    <artifactId>tycho-compiler-plugin</artifactId>
	    <version>${tycho.version}</version>
	    <extensions>true</extensions>
	    <dependencies>
		<dependency>
		    <groupId>org.eclipse.tycho</groupId>
		    <artifactId>tycho-compiler-jdt</artifactId>
		    <version>${tycho.version}</version>
		    <exclusions>
			<!-- Exclude the original JDT/Core to be replaced by the OT/J variant: -->
			<exclusion>
			    <groupId>org.eclipse.tycho</groupId>
			    <artifactId>org.eclipse.jdt.core</artifactId>
			</exclusion>
		    </exclusions>
		</dependency>
		<dependency>
		    <!-- plug the OT/J compiler into the tycho-compiler-jdt plug-in: -->
		    <groupId>org.eclipse</groupId>
		    <artifactId>objectteams-otj-compiler</artifactId>
		    <version>${otj.version}</version>
		</dependency>
	    </dependencies>
	</plugin>
    </pluginManagement>

So, what’s the difference? In both cases we need to adapt the tycho-compiler-jdt plug-in because that’s where we replace the normal JDT compiler with the OT/J variant. However, for plain OT/J applications tycho-compiler-jdt is pulled in as a dependency of maven-compiler-plugin and must be adapted on this path of dependencies, whereas in Tycho projects tycho-compiler-jdt is pulled in from tycho-compiler-plugin. Apparently, the exclusion mechanism is sensitive to how exactly a plug-in is pulled into the build. Interesting.

Once I figured this out, I created and published a new version of our Maven support for Object Teams: objectteams-parent-pom:2.1.1 — publishing Maven support for Object Teams 2.1.1 was overdue anyway 🙂

With the updated parent pom, a full OT/Equinox hello world pom now looks like this:

<project xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
 
    <parent>
        <!-- We use Object Teams: -->
        <groupId>org.eclipse</groupId>
        <artifactId>objectteams-parent-pom</artifactId>
        <version>2.1.1</version>
    </parent>
 
    <artifactId>OTEquinox-over-tycho</artifactId>
    <version>1.0.0-SNAPSHOT</version>
    <!-- We are building an Eclipse plug-in (or OSGi bundle): -->
    <packaging>eclipse-plugin</packaging>
 
    <repositories>
 
        <!-- This is where we get all Object Teams stuff from: -->
        <repository>
            <id>ObjectTeamsRepository</id>
            <name>Object Teams Repository</name>
            <url>http://download.eclipse.org/objectteams/maven/3/repository</url>
        </repository>
 
        <!-- Add any p2 repositories needed for your application, e.g.: -->
        <repository>
            <id>Juno</id>
            <name>Eclipse Juno Repository</name>
            <url>http://download.eclipse.org/releases/juno</url>
            <layout>p2</layout>
        </repository>
    </repositories>
 
    <build>
        <plugins>
            <plugin>
                <!-- We build this project using Tycho: -->
                <groupId>org.eclipse.tycho</groupId>
                <artifactId>tycho-maven-plugin</artifactId>
                <extensions>true</extensions>
            </plugin>
        </plugins>
    </build>
</project>

Looks pretty straight forward, right?

To see the full OT/Equinox Hello World Example configured for Maven/Tycho simply import OTEquiTycho.zip as a project into your workspace.

cheers,
Stephan

Written by Stephan Herrmann

October 31, 2012 at 00:16

Modularity at JavaOne 2012

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Those planning to attend JavaOne 2012 in San Francisco might be busy right now building their personal session schedule. So here’s what I have to offer:

On Wed., Oct. 3, I’ll speak about

Redefining Modularity and Reuse in Variants—
All with Object Teams

I'm Speaking at JavaOne 2012

I guess one of the goals behind moving Jigsaw out of the schedule for Java 8 was: to have more time to improve our understanding of modularity, right? So, why not join me when I discuss how much an object-oriented programming language can help to improve modularity.

When speaking of modularity, I don’t see this as a goal in itself, but as a means for facilitating reuse, and when speaking of reuse I’m particularly interested in reusing a module in a context that was not anticipated by the module provider (that’s what creates new value).

To give you an idea of my agenda, here’re the five main steps of this session:

  1. Warm-up: Debugging the proliferation of module concepts – will there ever be an end? Much of this follows the ideas in this post of mine.
  2. Reuse needs adaptation of existing modules for each particular usage scenario. Inheritance, OTOH, promises to support specialization. How come inheritance is not considered the primary architecture level concept for adapting reusable modules?
  3. Any attempts to apply inheritance as the sole adaptation mechanism in reuse mash-ups results in conflicts which I characterize as the Dominance of the Instantiator. To mend this contention inheritance needs a brother, with similar capabilities but much more dynamic and thus flexible.
  4. Modularity is about strictly enforced boundaries – good. However, the rules imposed by this regime can only deliver their true power if we’re also able to express limited exceptions.
  5. Given that creating variants and adapting existing modules is crucial for unanticipated reuse, how can those adaptations themselves be developed as modules?

At each step I will outline a powerful solution as provided by Object Teams.

See you in San Francisco!

5 items in your shopping cart Edit: The slides and the recording of this presentation are now available online.

Written by Stephan Herrmann

September 20, 2012 at 19:55

Object Teams 2.1 Milestone 7 (finally) brings hot code replacement

with 2 comments

As part of the Juno Milestone 7 also Object Teams has delivered its Milestone 7.

As the main new feature in this milestone hot code replacement finally works when debugging OT/J or OT/Equinox applications.

What took us so long to make it work?

  • Well, hot code replacement didn’t work out of the box because our load-time weaver only worked the first time each class was loaded. When trying to redefine a class in the VM the weaver was not called and thus class signatures could differ between the first loaded class and the redefined version. The VM would then reject the redefinition due to that signature change.
  • Secondly, we didn’t address this issue earlier, because I suspected this would be pretty tricky to implement. When I finally started to work on it, reality proved me wrong: the fix was actually pretty simple 🙂

In fact the part that makes it work even in an Equinox setting is so generic that I proposed to migrate the implementation into either Equinox or PDE/Debug, let’s see if there is interest.

Now when you debug any Object Teams application, your code changes can be updated live in the running debug target – no matter if you are changing teams, roles or base classes. Together with our already great debugging support, this makes debugging Object Teams programs still faster.

More new features can be found in the New&Noteworthy (accumulated since the Indigo release).

Written by Stephan Herrmann

May 12, 2012 at 22:10

Posted in Eclipse, Object Teams, OTDT, OTEquinox

Tagged with , ,

The message is the message

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I have been ranting about bad error messages, so in my own work, error messages better be helpful. At least I try.

As for the recent milestone 6 of the JDT a significant novelty was actually mostly about the wording of a few error/warning messages issued by the null analysis of the JDT compiler. We actually had quite a discussion (no, I’m not expecting you to read all the comments in the bug:)).

Why did we go through all this instead of using the time to fix more bugs? Because the entire business of implementing more compiler warnings and in particular introducing annotation-based null analysis is to help you to better understand possible weaknesses of your code. This means our job isn’t done when the error message is printed on your screen, but only when you recognize why (and possibly how) your code could be improved.

So the game is:
when you see one of the new compiler messages
“what does it tell you?

Intended “inconsistency”

Let’s start with an example that at first looks inconsistent:

Both methods basically have the same code, still lines 14-17 are free of any warnings whereas the corresponding lines 24-27 have one warning and even an error. What does it tell us?

Here are some of the messages:

line 10 Redundant null check: The variable val1 cannot be null at this location
line 12 Null comparison always yields false: The variable val1 cannot be null at this location

Before bug 365859 the second method would show the same messages, giving no clue why after the initial start all the same code gives different results later. The initial improvement in that bug was to update the messages like this:

line 20 Redundant null check: The variable val2 is specified as @NonNull
line 22 Null comparison always yields false: The variable val2 is specified as @NonNull

Alright! Here lies the difference: in the first method, compiler warnings are based on the fact that we see an assignment with the non-null value "OK" and carefully follow each data-flow from there on. Non-null definitely holds until line 15, where potentially (depending on where b takes the control flow) null is assigned. Now the check in line 16 appears useful.

By contrast, the warnings in the second method tell us, that they are not based on flow analysis, but on the mere fact that val2 is declared as of type @NonNull String. This specification is effectual, independent of location and flow, which has two consequences: now the assignment in line 25 is illegal; and since we can’t accept this assignment, line 26 still judges by the declaration of val2 which says: @NonNull:

line 25 Null type mismatch: required ‘@NonNull String’ but the provided value is null
line 26 Redundant null check: The variable val2 is specified as @NonNull

Communicate the reasoning

Three levels to a good error message:

  1. “You did wrong.”
  2. “Your mistake was …”
  3. “This is wrong because …”

By now you probably know what I think of tools that answer using (1). To go from (2) towards (3) we split one particular error message into three. Look at this:

which gives these error messages:

line 31 Null type mismatch: required ‘@NonNull String’ but the provided value is null
line 32 Null type mismatch: required ‘@NonNull String’ but the provided value is specified as @Nullable
line 34 Null type mismatch: required ‘@NonNull String’ but the provided value is inferred as @Nullable

Line 31 is obvious.

Line 32 is wrong because in is declared as @Nullable, saying null is a legal value for in, but since it’s not legal for tmp2 the assignment is wrong.

In line 34 we are assigning a value that has no nullness specification; we say, unknown has a “legacy” type. From that alone the compiler cannot decide whether the assignment in line 34 is good. However, using also information from line 33 we can infer that unknown (probably) has type @Nullable String. In this particular case the inference is obvious, but the steps that lead to such conclusion can be arbitrarily complex.

What does this distinction tell you?

The error in line 31 is a plain violation of the specification: tmp1 is required to be nonnull, but the assigment attempts to definitely break that rule.

The error in line 32 denotes the conflict between two contradictory declarations. We know nothing about actual runtime values, but we can tell without any doubt that the code violates a rule.

Errors of the type in line 34 are reported as a courtesy to the user: you didn’t say what kind of variable unknown is, thus normally the compiler would be reluctant to report problems regarding its use, but looking a bit deeper the compiler can infer some missing information. Only in this category it makes sense to discuss whether the conclusion is correct. The inference inside the compiler might be wrong (which would be a compiler bug).

Sources of uncertainty

Of the previous messages, only the one in line 31 mentions a runtime fact, the remaining errors only refer to possibilities of null values where no null value is allowed. In these cases the program might actually work – by accident. Just like this program might work:

void maybe(Object val) {
   System.out.println(val.toUpperCase());
}

While this is not a legal Java program, a hypothetical compiler could produce runnable byte code, and if the method is invoked with an argument that happens to be a String, all is well – by accident.

While we have no guarantee that things would break at runtime, we know for sure that some rule has been broken and thus the program is rejected.

The following method shows a different kind of uncertainty:

What can we tell about this assignment? Well … we don’t know, it’s not definitely bad, but it’s not good either. What’s the problem? We need a @NonNull value, but we simply have no information whether unspecified can possibly be null or not. One of those legacy types again. After much back and forth we finally found that we have a precendent for this kind of problem: what’s the compiler say to this snippet:

void safety2(List unspecified) {
    List<String> strings = unspecified;
}

Right, it says:

Type safety: The expression of type List needs unchecked conversion to conform to List

meaning: we receive an argument with a type that lacks detailed specification, but we require such details on the left hand side of the assignment. Whether or not the RHS value matches the LHS requirement cannot be checked by the compiler. Argument unspecified has another kind of legacy type: a raw type. To gracefully handle the transition from legacy code to new code with more complete type specifications we only give a warning.

The same for null specifications:

line 41 Null type safety: The expression of type String needs unchecked conversion to conform to ‘@NonNull String’

In both cases, raw types and types lacking null specification, there are situations where ignoring this warning is actually OK: the legacy part of the code may be written in the full intention to conform to the rule (of only putting strings into the list / using only nonnull values), but was not able to express this in the expected style (with type parameters / null annotations). Maybe the information is still documented, e.g., in the javadoc. If you can convince yourself that the code plays by the rules although not declaring to do so: fine. But the compiler cannot check this, so it passes the responsibility to you, along with this warning.

Tuning comiler messages

If you buy into null annotations, the distinction of what is reported as an error vs warning should hopefully be helpful out of the box. Should you wish to change this, please do so with care. Ignoring some errors can render the whole business of null annotations futile. Still we hope that the correspondence between compiler messages and configuration options is clear:

These options directly correspond to the messages shown above:

problems controlled by this option
lines 31,32 Violation of null specification
line 34 Conflict between null annotations and null inference
line 39 Unchecked conversion from non-annotated type to @NonNull type

Conclusion

The compiler does an awful lot of work trying to figure out whether your code makes sense, definitely, or maybe, or maybe not, or definitely not. We just decided, it should try a little harder to also explain its findings. Still, these messages are constrained to be short statements, so another part of the explanation is of course our job: to educate people about the background and rationale why the compiler gives the answers it gives.

I do hope you find the messages helpful, maybe even more so with a little background knowledge.

The next steps will be: what’s a good method for gradually applying null annotations to existing code? And during that process, what’s a good method for reacting to the compiler messages so that from throwing code at the compiler and throwing error messages back we move towards a fruitful dialog, with you as the brilliant Holmes and the compiler your loyal assistant Watson, just a bit quicker than the original, but that’s elementary.

Written by Stephan Herrmann

April 15, 2012 at 01:53

Posted in Eclipse

Tagged with , , , ,

Using git for an interactive video – Replay the JDT tutorial

with 2 comments

When preparing the tutorial How to train the JDT dragon, Ayushman and me packed way more material than we could possible teach in 3 hours time.

Luckily, Ayush came up with an idea that enables all of you to go through the exercise all on your own: instead of creating zip files with various stages of the example projects, we pushed everything to github. I apologize to those who were overwhelmed by how we pushed git onto the tutorial participants in Reston.

Now, as EclipseCon is over, here’s what you can do:

  • Fetch the slides: PDF or slideshare
  • Clone the material for the plain JDT part (git: URL), containing two projects for the first two exercises.
    • org.eclipsecon2012.jdt.tutorial1: traverse the Java Model starting from the element selected in the UI
    • org.eclipsecon2012.jdt.quickFix1: implement a quickfix for adding a missing null check
  • Clone the misc repo (git: URL), containing
    • handouts: instructions for the exercises
    • org.eclipsecon2012.jdt.populator: plug-in that was used in the tutorial to create sample content in the runtime workbench; show cases how to programmatically create Java files from String content
  • Clone the OT repo (git: URL), containing
    • AntiDemo: the OT/Equinox hello-world: prohibition of class names starting with “Foo”.
    • Reachability: a full blown reachability analysis in < 300 LOC.

The last exercise, “Reachability”, we couldn’t even show in Reston, but luckily this is the most detailed repo: in 13+1 commits I recorded the individual steps of adding inter-procedural reachability analysis piggy-back on top of the JDT compiler. If you replay these commits from the git repo you can watch me creating this little plug-in from scratch. Starting from step 5 you’ll be able to see the results when you fire up a runtime workbench: the analysis will print to stdout what methods it found during each full build.

Look at the commit comments which summarize what I would have explained in demo mode. Still the material is pretty dense as it explains three technologies at the same time:

  1. How does this analysis work?
  2. What points in the JDT do we hook onto?
  3. How is the integration achieved using Object Teams.

Speaking of integration: using the “Binding Editor” you can see all bindings in a tabular view:

Bindings of the Reachability plug-in

The right hand side of the table give the full list of JDT elements we connect to:

  • classes that are extended using a role_obj role
  • methods/fields that are accessed externally via a callout binding callout binding
  • methods that are intercepted using a callin binding (after) callin binding.

As a special bonus, step 14 in the git repo shows how to add problem markers for each unreachable method, so that the JDT will actually offer its existing quickfix for removing:
Unreachable methods
(Yep, both methods are detected as unreachable: calling each other without being called from another reachable method doesn’t help).

I hope you enjoy playing with the examples. For questions please use one of the forums:

Written by Stephan Herrmann

April 7, 2012 at 15:20

Thanks Eclipse!!

with one comment

Wow! I’m totally flattered. Last night I received this shiny trophy:

Basically, my involvement in Eclipse has two simple reasons:

  • Given that the JDT is the favorite IDE of so many smart Java developers, it’s a real treat to be able to take part in its constant improvement still. Making unsolicited comments to other components of the bunch just adds to the fun.
  • Given the success of Java and the JDT, it’s a thrill to lift both of them to new dimensions in the Object Teams project. Have a deep look and you’ll think differently about objects and modularity.

If you feel similarly in any regard but aren’t involved yet, don’t feel shy: none of the Eclipse components is to be worshiped in a museum, but all over the place new contributors are essential for keeping this great piece of software fresh and alive in its second decade. I’m looking forward to next years Top Contributor! (Yet, I will not pass on my little trophy :)).

Thanks to all, and especially to the JDT team, for having me!

BTW: EclipseCon 2012 in Reston is the best EclipseCon 2012 ever!

Written by Stephan Herrmann

March 28, 2012 at 03:53

Posted in Eclipse

Help the JDT Compiler helping you! – 3: The essence of null annotations

with 2 comments

After my little excursion to detecting resource leaks let me return to our favorite bug: NPE.

Basic support for null annotations was big news at the release of the Eclipse SDK Juno M4.

To fully understand the approach it’s good to sit back and think of what exactly we’re telling the compiler when we add null annotations to a program.

Annotations as filters

One could certainly use the annotations to mean the following:

@NonNull
“I don’t think this variable will ever hold a null, no need to warn me, when I dereference that value.”
@Nullable
“I guess this variable could be null, so please warn me when I forget a null check before dereferencing.”

Interpreted in this way, the annotations would already be helpful, and actually this would rank them in the same category as @SuppressWarnings("null"): no matter what the compiler analyzed up-to this point, please take my word that this thing is / is not dangerous. In both cases we’d ask the compiler to look at certain things and ignore others, because we “know better”.

However, telling the compiler what’s dangerous and what’s not puts the cart before the horse. If I do so, I will be the weakest link in the chain of analysis. I could err, I do err – that’s why I have NPEs in the first place, so I shouldn’t tell the compiler to trust my judgment.

The good news is: when used appropriately null annotations provide a lot more help.

Annotations as an extension of the type system

The essence of static typing

Lets step back and imagine Java wouldn’t have static typing. A variable declaration would be nothing more than a name, introduced -say- using an imaginary keyword var:

   var o;
   o = new Person();
   o.meow();
 

Right, we could now assign any object, any value, to the variable o and on the other hand we could attempt to invoke any method. Only at runtime will we notice whether the object refered to by o actually has a method meow(). Obviously, this code is unsafe, it could abort saying “Message on understood”. As Java programmers we don’t accept this unsafety, so we use types as a specification:

A typed variable declaration adds a specification with these two sides:

  • It adds a constraint such that only certain values can legally be assigned to the variable
  • It establishes a guarantee that certain operations are well-defined wrt the value of the variable.

A statically typed language forces a decision: what values do I want to allow to be bound to the variable? If I declare o as of type Cat the compiler can conclude that “o = new Person();” violates the constraint and cannot be accepted. If, OTOH, I declared o as of type Person the compiler won’t complain at the assignment but typically it will not find a meow() method in a class Person so that line is now illegal. Only if all things match: the declaration, the assignment, and the usage of a variable, only then will the compiler accept the program and certify that this program will not raise “Message not understood”. It’s a trade: constraint for guarantee.
In a statically typed language we are constrained in what we can say, but we gain the guarantee that a certain kind of error will not occur at runtime.

Sounds fair?

More constraints – more guarantees

Standard static typing constrains the program such that values match to the operations we perform with these values, except – there’s a big loop-hole: in traditional object-oriented type systems each class type contains a value that is not suitable for most operations: the value null, which Tony Hoare called his “billion dollar mistake”.

At a closer look, static type checking in Java is founded on a contradiction:

  • When analyzing an assignment assume that null is a legal value for every object type.
  • When looking at a method call / a field reference assume that null cannot occur (otherwise no unchecked dereference could be considered as legal).

This is exactly, what null annotations fix: they split each traditional object type into two types:

@NonNull Cat
This is the type that contains only cat values
@Nullable Cat
This is the union of the above type and the null-type which contains only one value: null

You can read the type @Nullable Cat as: either a cat or null.

Null warnings vs. type errors

Those users who try the new feature in the JDT may be surprised to see a whole new kind of error messages. While the original goal is to get alerted about potential NPEs, the compiler may now complain with messages like:

Type mismatch: required ‘@NonNull Cat’ but the provided value can be null

The question may arise, why this is reported as an error, even if no NPE can be directly caused at the statement in question. The answer can be deduced from the following analogy:

void foo(Object o, @Nullable Cat c) {
    Cat aCat = o;                 // "Type mismatch: cannot convert from Object to Cat"
    @NonNull Cat reallyACat  = c; // "Type mismatch: required '@NonNull Cat' but the provided value can be null."
}
 

(The wording of the second message will be still improved to better reflect different kinds of RHS values).

The analogy shows:

  • The assignment itself could actually succeed, and even if types don’t match, a language without static typing could actually accept both assignments.
  • If, however, the assignment were accepted, all subsequent analysis of the use of this variable is useless, because the assumption about the variable’s type may be broken.

Therefor, a first step towards making NPE impossible is to be strict about these rules. Assigning a value to a @NonNull variable without being able to prove that the value is not null is illegal. Just as assigning an Object value to a Cat variable without being able to prove that the value is indeed a cat is illegal.

Interestingly, for the first assignment, Java offers a workaround:

    Cat aCat = (Cat) o;
 

Using the cast operator has two implications: we tell the compiler that we “know better”, that o is actually a cat (we do believe so) and secondly, as compiler and JVM cannot fully trust our judgment a check operation will be generated that will raise a ClassCastException if our assumption was wrong.

Can we do something similar for @NonNull conversion? Without the help of JSR 308 we cannot use annotations in a cast, but we can use a little helper:

void foo(Object o, @Nullable Cat c) {
    @NonNull Cat reallyACat  = assertNonNull(c);
}
@NonNull  T assertNonNull(T val) {
    if (val == null) throw new NullPointerException("NonNull assertion violated");
    return val;
}
 

corrected on 2012/03/05

What? We deliberately throw an NPE although the value isn’t even dereferenced? Why that?

The helper mimics exactly what a cast does for normal type conversions: check if the given value conforms to the required type. If not, raise an exception. If the check succeeds re-type the value to the required type.

Here’s an old school alternative:

void foo(@Nullable Cat c) {
    @SuppressWarnings("null") @NonNull Cat reallyACat  = c;
}
 

(Requires that you enable using @SuppressWarnings for optional errors).

Which approach is better? Throwing an exception as soon as something unexpected happens is far better than silencing the warning and waiting for it to explode sometime later at some other location in the code. The difference is felt during debugging. It’s about blame assignment.
If things blow up at runtime, I want to know which part of the code caused the problem. If I use @SuppressWarnings that part is in stealth mode, and an innocent part of the code will get the blame when it uses the wrong-typed value.

Remember, however, that cast and assertNonNull are not the solution, those are workarounds. Solutions must explicitly perform the check and provide application specific behavior to both outcomes of the check. Just as a cast without an instanceof check is still a land-mine, so is the use of the above helper: NPE can still occur. If you need to dereference a variable that’s not @NonNull you should really ask yourself:

  • How can it happen that I end up with a null value in this position?
  • How can the application safely and soundly continue in that situation?

These questions cannot be answered by any tool, these relate to the design of your software.

Help the JDT compiler helping you

This post showed you two things you can and should do to help the compiler helping you:

Add null annotations to resolve the contradiction that’s inherent in Java’s type system: a type can only either contain the value null or not contain the value null. Still Java’s type system opportunistically assumes a little bit of both. With annotations you can resolve the ambiguity and state which of the two possible types you mean.

Second, listen to the new type error messages. They’re fundamental to the analysis. If you disregard (or even disable) these messages there’s no point in letting the analysis apply all its sophisticated machinery. From false assumptions we cannot conclude anything useful.

If you apply these two hints, the compiler will be your friend and report quite some interesting findings. For a project that uses null annotations right from the first line of code written, this advice should be enough. The difficult part is: if you have a large existing code base already, the compiler will have a lot to complain. Think of migrating a fully untyped program to Java. You bet you could use some more help here. Let’s talk about that in future posts.

Written by Stephan Herrmann

February 21, 2012 at 20:39

Posted in Eclipse

Tagged with , , , ,