{"id":1713,"date":"2013-09-20T16:08:37","date_gmt":"2013-09-20T04:08:37","guid":{"rendered":"https:\/\/www.deltics.co.nz\/blog\/?p=1713"},"modified":"2013-09-20T16:42:30","modified_gmt":"2013-09-20T04:42:30","slug":"how-to-call-java-code-from-an-oxygene-android-application","status":"publish","type":"post","link":"https:\/\/www.deltics.co.nz\/blog\/posts\/1713\/","title":{"rendered":"How to Call Java Code from an Oxygene Android Application"},"content":{"rendered":"[Estimated Reading Time: <\/span> 2<\/span> minutes]<\/span><\/span>

Lachlan just posted<\/a> a link to a post on Google+<\/a> (also available as a PDF<\/a>) demonstrating how to call Java from Delphi XE5.<\/p>\n

<\/p>\n

I was shocked at both the amount<\/em> and the nature<\/em> of the code involved. It is long, convoluted and ugly stuff (nb.<\/strong> that isn’t a criticism of Paul’s code; such techniques rarely if ever result in elegant solutions<\/em>) indeed sometimes requiring you to resort to using tools to reverse engineer the Java code. Certainly not for the faint hearted.<\/p>\n

In Oxygene<\/strong> things are much simpler because when compiling with Oxygene for Java<\/strong>, Oxygene<\/strong> code is<\/em><\/strong> Java<\/strong> code, it’s just not written in the Java language<\/em>.<\/p>\n

The Comparison<\/h3>\n

Paul Foster’s post ends with an example of calling a getIntValue<\/strong> and setIntValue<\/strong> method on some Java class that he wrote to test the technique. For the purposes of providing a more convenient, side-by-side comparison I hope he doesn’t mind if I reproduce that last snippet here:<\/p>\n

\r\nvar\r\n  jLoadedClassID,jLoadedObjectID:JNIObject;\r\n  jGetMethod,jSetMethod:JNIMethodID;\r\n  JavaEnv:PJNIEnv;\r\n  jiReturnedValue:JNIInt;\r\n  jvValuetoSet:JNIValue;\r\nbegin\r\n  {...don\u2019t forget the other bits first!}\r\n\r\n  jiReturnedValue:=JavaEnv^.CallIntMethodA(JavaEnv, jLoadedObjectID,jGetMethod);\r\n\r\n  jvValuetoSet.i:=1234567890;\r\n  JavaEnv^.CallVoidMethodA(JavaEnv, jLoadedObjectID, jSetMethod,@jvValuetoSet);\r\nend;\r\n<\/pre>\n
As you can see, this isn’t complete – there’s pre-amble needed to make all this work and I encourage you to read his article in full to appreciate just how much and what is involved.<\/p>\n
By contrast, here’s the Oxygene<\/strong> code that achieves the same:<\/p>\n
\r\n  var\r\n    loadedObject: MyJavaClass;\r\n    returnedValue: Integer;\r\n  begin\r\n    \/\/ get the reference to loadedObject from somewhere ...\r\n\r\n    returnedValue := loadedObject.getIntValue;\r\n\r\n    loadedObject.setIntValue(1234567890);\r\n  end;\r\n<\/pre>\n
Or, if you prefer to take advantage of the fact that Oxygene recognises that get<\/strong>\/set<\/strong> methods can be treated as properties, and prefer the more Pascal-like syntax this permits:<\/p>\n
\r\n    returnedValue := loadedObject.IntValue;\r\n\r\n    loadedObject.IntValue := 1234567890;\r\n<\/pre>\n
Important Firsts<\/h3>\n
Oxygene for Java<\/strong> is just one part of Oxygene<\/strong> product.  When you purchase Oxygene<\/strong> you get:<\/p>\n