Ada95 Lovelace Tutorial Section 16.8 (2024)

It makes sense to close a discussion of Ada and Java by comparing the twolanguages.

Ada and Java have more similarities than differences. Both the Ada languageand the Java language were designed with safety in mind(both support strong typing, omit pointers, and perform many compile-timeand run-time checks).Both support an object-oriented approach based on a singleinheritance hierarchy.When generating class files,both Ada and Java support garbage collection, multitasking,and platform-independentgraphical user interfaces (GUIs).

There are differences, of course. Here are some technical advantages ofthe Ada language over the Java language(SigAdahas a similar list):

1. Ada supports enumerated types.
2. Ada supports operator overloading for infix operators (for example,you can define an infix + operation for complex numbers).
3. Ada supports generics. There is no Java equivalent, thoughJava's "Interface" and its root Object class cansometimes be used to do similar things.
4. Ada supports "in", "out", and "in out" to document the use of parameters,and these modifiers work on both tagged types and scalars.
5. Ada is easier to read in some cases (compare "and" with "&&";compare "for I in 1..10" with "for (i=1; i <= 10; i++)";compare "a=b" with "a==b").
6. Ada permits array boundaries to start with any scalar. The Java languagerequires array boundaries to start at 0, a common source of "one-off" errors.
7. Ada supports numeric range checks more specific than the built-in types.This can be used to detect errors that Java doesn't.
8. Ada supports method calls using named and unordered parameters,and supports default parameter values.
9. Ada supports subprogram access types and nested subprograms.

Java has some technical advantages over Ada, too:

1. Java supports "interface" types.There is no standard Ada equivalent, thoughAda generics and the nesting of objectscan sometimes be used to do similar things.Ada programs that generate Java code can use and define Java interfaces,using a special pragma to do so.
2. Java permits specifications to be circular (A depends on B which dependson A), while Ada does not. There is some argument that this is a disadvantage,since circular references can indicate poorly structured systems, but interms of ease-of-use this is an advantage.
3. Java class definitions tend to be shorter than Ada.Here are some of the reasons for this:
   1. Ada enforces a distinction between objects and access valuesto objects.This causes definitions to be longer (for example, in Ada you have to defineX_Obj and X_Ptr types everywhere, while all of that is not usedin the Java language).
   2. Ada requires an explicit list of all classes used ("with" statements) in aclass being defined.Java does not require a list of classes used; the closest Java has isits "import" statement, which is like the "use" clause in Ada.
   3. Java has an implicit "this" parameter for non-static methods; Ada requiresall parameters to be explicitly listed.
   4. Java interfaces have to be handled using a somewhat clumsy Ada syntax.
4. Java supports hierarchies of exception definitions. Java also includesdefinitionsof exceptions that might be thrown (raised) by each method as part of themethod definition.

Naturally, more than technical issues make a decision. Here are some otherissues regarding the use of the Java language and Ada language for creatingJava applets and applications:

1. There are a number of tooling issues.At the time of this writingthere are more Ada compilers than Java compilers, but by the time you readthis there should be many compilers for both languages.Most Ada compilersgenerate native (high-speed) code that can take advantage of the underlyinghardware, while Java compilers are just beginning to appear.However, currentlyonly one Ada compiler can generate class files and applets, so the quantityof compilers tilts towards Javaif you're solely interested in generating applets and/or class files.You'll also need to compare the tool capabilities themselves: which havebetter interactive development environments (IDEs)?Which have additional functionality (like user interface generators) thatyou'd like?Since just-in-time Java compilers that take class files can compile both Javaand Ada class files, the choice of language is irrelevantfor just-in-time compilers.
2. There are large reusable component libraries for both languages, each withdifferent focuses.Compare the relevant reusable componentsin the different languages for your application.
3. There is an ISO (international) standard for Ada, while a standard for Javais probably many years away (at the time of this writing).
4. There is a large standard test suite for Ada compilers; none yet existsfor Java.
5. There are sometimes vendor restrictions prohibiting use of theJava languagefor safety-critical systems; Ada is commonly used in such areas, and compilerscan be bought without such prohibitions.
6. The use ofJavain real-time applications is somewhat currently a research area,while Ada is already used in such areas and has been for many years.
7. Most Java materials and tools assume that users are usingthe Java language.Thus, if you're developing a Java application in Ada you'll need tolearn the translation conventions (as discussed in previous sections) andbe able to make such translations mentally.No such translations are needed if you're using the Java language.

Quiz:

Which of the following statements is true?

1. The Java language lets you write your own infix operators, whilethe Ada standard supports interface types and hierarchical exceptions.
2. A web browser that includes a just-in-time compiler for class filescan't compile programs written in Ada.
3. When generating Java class files, both Ada and Java supportgarbage collection and a standard graphical user interface.

1. Statement 1.
2. Statement 2.
3. Statement 3.

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