Per the java.util.function Javadoc,

Since:
      1.8

So upgrade to Java 8, or try to find an older version of the tutorial.

I'm new at this. How can you tell what you are running? I'm using Eclipse

To determine your current Java version in eclipse, go to

Help -> About Eclipse -> Installation Details (Button in
          lower Left) -> Configuration pane

Look for the line java.specification.version - on my machine that is

java.specification.version=1.8

Or the line java.runtime.version - on my machine that is

java.runtime.version=1.8.0_11-b12

You will need to pass myfunc as a method reference.

Try this:

public void callFunc() {
    fSupplier(this::myfunc);
}

Assuming that your logger is a java.util.logging.Logger . . .

According to the Javadoc for Logger.info, it expects a Supplier<String>, and you're giving it a Supplier<Double>.

To fix this, you need to give it a Supplier<String>. You can write one either like this:

Copyfinal Supplier<String> randomSupplier =
    new Supplier<String>() {
        public String get() {
            return Double.toString(Math.random());
        }
    };

or like this:

Copyfinal Supplier<String> randomSupplier =
    () -> Double.toString(Math.random());

You can even write:

Copylogger.info(() -> Double.toString(Math.random()));

and Java will magically infer that your lambda is meant to be a Supplier<String> (because the other overload of info doesn't take a functional interface type).