PROPOSAL: open and close brace optional for single statement try, catch, finally, method declaration

[Glenn A.P. Marshall]

PROJECT COIN SMALL LANGUAGE CHANGE PROPOSAL FORM v1.0

AUTHOR(S): Glenn Marshall

*OVERVIEW

FEATURE SUMMARY:

Make open and close brace optional for single statement try, catch,  
finally, method declaration.

(the relatively rarely used single statement static initializer would  
still require braces under this proposal, due to its relative rarity).

MAJOR ADVANTAGE:

Simple, single statement try blocks, catch blocks, and single  
statement methods (for example, getter methods) are very common in  
Java code.  Unlike if, while and do statements, the open and close  
braces are mandatory even when the target of the keyword is a single  
statement.  This requirement needlessly clutters the code with  
unneeded open and close braces, increases code complexity slightly  
and decreases readability.  Removing this requirement addresses a  
syntactic inconsistency in Java, whereby braces are required for some  
single statement keyword targets but not others.

MAJOR BENEFIT:

More readable code, needless syntactic 'noise' removed, consistent  
treatment of common single statement keyword targets.  Since single  
statement try, catch, method are very common, these benefits could be  
applied many times to a typical large Java program.

MAJOR DISADVANTAGE:

Implementation cost is not 0. Benefits are relatively minor, to be  
fair, per instance.  Single statement keyword targets still exist -  
static initializers; the syntax is still not 100%  consistent as  
regards single statement keyword targets.

ALTERNATIVES:

None.

* EXAMPLES

SIMPLE EXAMPLE:

try connection.close();
catch (SQLException se) handleException("close failed", se);

...

public String getName() return name;


ADVANCED EXAMPLE:

(this proposal is very simple; there are no advanced examples)

*DETAILS

SPECIFICATION: Describe how the proposal affects the grammar, type
system, and meaning of expressions and statements in the Java
Programming Language as well as any other known impacts.

The grammar would be modified to make braces optional for single  
statement try, catch, finally, method declarations.  The block still  
exists, when braces are omitted; it is a single statement.  This is  
exactly analogous to (for example) single statement while statements  
without braces.

This is purely a syntactic change - the type system, meaning of  
expressions and statements remain unchanged.

COMPILATION: How would the feature be compiled to class files?

The simplest implementation would be for  the Java source code parser  
to recognize when the braces have been omitted and add them back,  
internally, conceptually.  This eliminates any downstream impact.

TESTING: How can the feature be tested?

Extend the source code samples processed by the compiler test suite  
to include  samples of code using this feature.  Remember to handle  
the null statement.

LIBRARY SUPPORT: Are any supporting libraries needed for the feature?

No.

REFLECTIVE APIS: Do any of the various and sundry reflection APIs need
to be updated? This list of reflective APIs includes but is not limited
to core reflection (java.lang.Class and java.lang.reflect.*),
javax.lang.model.*, the doclet API, and JPDA.

No

OTHER CHANGES: Do any other parts of the platform need be updated too?
Possibilities include but are not limited to JNI, serialization, and
output of the javadoc tool.

No.

MIGRATION: Sketch how a code base could be converted, manually or
automatically, to use the new feature.

Look for sequences of if try { <single statement>; } and replace with  
try <single statement>.

Also for catch, method definitions, finally.

COMPATIBILITY
BREAKING CHANGES: Are any previously valid programs now invalid? If so,
list one.

All existing programs remain valid.

EXISTING PROGRAMS: How do source and class files of earlier platform
versions interact with the feature? Can any new overloadings occur? Can
any new overriding occur?

The semantics of existing class files are unchanged.  Source code  
that previously omitted these required braces would not compile due  
to a syntax error; this source will now compile.  Compiler test cases  
that tested this behaviour, expecting to fail, will now pass.

* REFERENCES

EXISTING BUGS:

(none found)

URL FOR PROTOTYPE (optional):

No prototype at this time.