[jdt-core-dev] Compiling against JDK8 but staying compatible with 1.7 by

[Tom Schindl <tom.schindl@xxxxxxxxxxxxxxx>]

Hi,

I'm in the position that I have to compile against JDK8 (because of 
libraries contained in there) but the .class file should still be 
useable in Java7.

Now I tried put the following settings in a project which runs against 
the BETA_JAVA8 branch.

> eclipse.preferences.version=1
> org.eclipse.jdt.core.compiler.codegen.inlineJsrBytecode=disabled
> org.eclipse.jdt.core.compiler.codegen.targetPlatform=1.7
> org.eclipse.jdt.core.compiler.codegen.unusedLocal=preserve
> org.eclipse.jdt.core.compiler.compliance=1.7
> org.eclipse.jdt.core.compiler.debug.lineNumber=generate
> org.eclipse.jdt.core.compiler.debug.localVariable=generate
> org.eclipse.jdt.core.compiler.debug.sourceFile=generate
> org.eclipse.jdt.core.compiler.problem.assertIdentifier=warning
> org.eclipse.jdt.core.compiler.problem.enumIdentifier=warning
> org.eclipse.jdt.core.compiler.source=1.8

As a test I've created a project which looks like this:

> import java.util.AbstractList;
> import java.util.Comparator;
>
>
> public class Test extends AbstractList<String> {
> 	private String[] internal = {"Hello","World"};
>
> 	@Override
> 	public void sort(Comparator<? super String> c) {
> 		// TODO Auto-generated method stub
> 		
> 	}
>
> 	@Override
> 	public String get(int index) {
> 		return internal[index];
> 	}
>
> 	@Override
> 	public int size() {
> 		return internal.length;
> 	}
> 	
> }


> import java.util.function.Consumer;
>
>
> public class Bla {
>
> 	public static void main(String[] args) {
> 		System.err.println("HELLO WORLD");
> 		Test t = new Test();
> //		t.forEach(new Consumer<String>() {
> //
> //			@Override
> //			public void accept(String t) {
> //				System.err.println("Value: " + t);
> //			}
> //		});
> 		
> 		for( String s : t ) {
> 			System.err.println(s);
> 		}
> 		
> 	}
>
> }

And the code runs fine in Java7 and Java8. My question now is does this 
only work by chance, or is it possible to compile to 1.7 bytecode if no 
1.8 features are used?

From https://bugs.eclipse.org/bugs/show_bug.cgi?id=390889 I somehow 
have the feeling that this is not supposed to work at all.

Tom