Does changing the Java library make it possible to optimize the code?

Question

Java

Let's say there is code written in the Java 6 library. If we reconfigure the library, let's say in the same Eclipse, connecting instead of 1.6 - 1.8. In this case, it will be possible to change the parts of the code that I do not like, using all the features of Java 8?
And if so, what are the pitfalls?

Answer 1

You can only use java 8 features if you are compiling the project with jdk 8, just changing the option in eclipse won't do anything. What is the question is not at all clear.