How to target a lower language level in Java

Question

I maintain a Java tutorial application written in Java, that demonstrates features of Java 6, 7, and 8. Each tutorial screen is loaded dynamically by Class.forName as needed. The Java 7 classes need to use Java 7 constructs, and the Java 8 classes need to use Lambdas and Date/Time API.

I would like this to be accessible to users of all three of those language levels, just that if they are on Java 6 we would not load up the Java 7 or 8 classes, and if on 7 we would not load the Java 8 classes.

We would dynamically determine the runtime level and disregard higher levels, loading only the relevant classes by Class.forName(). Obviously users with Java 6 or 7 would not be able to execute code with a magic number of 8. So I would like to target an earlier Java release in the build.

In other words, I would like to set source to 1.8 and target to 1.6

However Maven (and Javac) prevent me from specifying a target lower than the source.

Is there any other way?

I have done this in the past with JavaFX code for Android, where I was able to build JavaFX 8 code using Lambdas, but then deploy it to current Android versions. But in that case, there was a special SDK that handled the lambdas and built to Java 7.

Is there any way to do that with standard Java 8?

Answer 1

The only option you have is -source 1.1 -target 1.0 In every other case, they have to be the same

You need to build a jar for each version and another which combines them.

Answer 2

You will have to make 3 different jars, one for each version where the later version include more of your code examples. (on the bright side, you just have to recompile the the java 6 and 7 code multiple times)

for each jar set the -target code to 6, 7 or 8 respectively. You can optionally also use -source parameter and set it to the same value but I don't think you need to unless you are worried you accidentally put in later language features.