集合(Map/List/Set)的初始化 以下答案来自Stackoverflow,建议各位初学者善加利用这个网站: Array: How do I declare and initialize an array in Java List: How to initialize an ArrayList 全面版: Initialization of an ArrayList in one line Double Brace Initialization Efficiency of Java “Double Brace Initialization” Map: How to directly initialize a HashMap (in a literal way)