检测无字符的最佳Java 8字符方法是什么？

I've got a simple program, written in Java, and I am trying to find a way to validate that anything at all has been entered before the user hits "enter" in the console. Currently, I'm using isLetter() to ensure that a letter has been entered, but this doesn't seem to prevent someone from entering nothing and hitting enter. I've tried several methods in the documentation, and can't seem to locate one that works. I've got a simple program, written in Java, and