GC of lambdas in java 8

gistfile1.java

import java.lang.ref.WeakReference;

import java.util.WeakHashMap;

public class Test {

    /**
     * Still don't know why the first two lambdas don't get cleared by the GC :(
     */
    public static void main(String[] args) throws Exception {

        WeakHashMap<Runnable, Boolean> map = new WeakHashMap<>();

        //these two don't get cleared by the garbage collector
        map.put(() -> System.out.println("lambda"), true);
        map.put(() -> System.out.println("lambda"), true);

        //this one does
        int i = 10;
        map.put(() -> System.out.println(i), true);

        //so does this one
        map.put(new Runnable() {
            @Override
            public void run() {
                System.out.println("anonymous inner class");
            }
        }, true);

        int count = 0;
        while (!map.isEmpty() && count++ < 6) {
            System.gc();
            Thread.sleep(50);
        }

        //size should be 0 by now, but is 2
        System.out.println("size() : " + map.size());
    }
}