assert ma.addMetaIfAbsent(attr2, 2) == 1; assert ma.addMetaIfAbsent(attr3, 3) == 3; assert ma.addMetaIfAbsent(attr2, new Callable<Integer>() { @Override public Integer call() throws Exception { return 5; assert ma.addMetaIfAbsent(attr4, new Callable<Integer>() { @Override public Integer call() throws Exception { return 5;