java 8 is a upgraded version of java7, Java7 is no longer supported and has a few differences to Java6 (project coin). Java8 is a massive leap forward with loads of new features including proper functional programming with Lambda, default methods, integral JavaFX, Nashorn for JavaScript, streams). Unless you desperately need to program in Java7 as predefined target platform, go for Java8.
Following are the features newly added in Java 8 -
Language-level support for lambda expressions; unofficially under Project Lambda
Default methods (virtual extension methods) which make multiple inheritance possible in Java.
a JavaScript runtime which allows developers to embed JavaScript code within applications.
Annotation on Java Types.
Unsigned Integer Arithmetic.
Repeating annotations.
Date and Time API.
Statically-linked JNI libraries.
Launch JavaFx applications.
