Reading Generated Sources

Class name mapping

Since J2ObjC only translates non-UI Java classes, an iOS application needs to directly work with the translated classes. Translated classes are regular NSObject-rooted Objective-C classes, but it helps to understand how class, method, parameter and header file names are converted.

Java uses packages to define namespaces, while Objective-C doesn't have packages and instead has a convention of putting a shared prefix in front of related classes (like NSObject and NSString). To preserve Java namespaces, package names are mapped to a camel-cased prefix. For example, java.util.List is mapped by default to JavaUtilList. This default prefix can be explicitly set using j2objc's package prefix options.

Parameter names

Java differentiates overloaded methods by their argument types, while Objective-C uses argument names. J2ObjC therefore creates argument names from their types. For example, here is how an object is inserted into the beginning of an ArrayList, and how that list is then added to another list:

[someList addWithInt:0 withId:object];
[otherList addAllWithJavaUtilCollection:somelist];

Each argument name consists of "with" plus its type. This is a bit ugly, but ensures that the same method is always invoked in Objective-C as it was with Java.

Header names

Header files do not have their names mapped, however, but instead have the Java source file path ending with ".h" instead of ".java". This makes supporting tools like Xcode and Make much easier, but can be a little confusing at first, since:

#import "java/util/Date.h"

declares the JavaUtilDate class, not Date.

Using translated classes

Other than the odd names (which can be simplified with package prefixes), translated classes are used like any other Objective-C class:

#import "java/util/BitSet.h"
  JavaUtilBitSet *bitset = [[JavaUtilBitSet alloc] init];
  [bitset setWithInt:10 withBOOL:YES];
  BOOL b = [bitset getWithInt:10];