Compilation in Java 7 - a method that uses Java 8 types

Question

I need to write code to handle dates. We are slowly moving from Java 7 to Java 8, so my library code should work with both. For this reason, it must have compiled Java 7.

However, projects already ported to Java 8 started using JSR-310 types.

Consider the following statements

if (obj instanceof Date){
    //Serialize using SimpleDateFormat
} else if (obj instanceof org.joda.time.LocalDateTime){
    //Serialize using Joda
} else if (obj instanceof java.time.LocalDateTime){
    //Serialize using JSR 310
}

I do not use Lambdas or other language materials provided by Java 8. In any case, I use the Java 8 compiler. I want to create Java-compatible code (no UnsupportedClassVersionError), which breaks when the third one, if the branch gets into Java 7 ( NoClassDefFoundError).

Currently, the above code does not compile at all if I use the Java 8 javac compiler for the target Java 7.

I am running Ant in Java 8

<javac includeantruntime="false" srcdir="src" destdir="build/compiled" target="1.7" source="1.7"

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