Strategy pattern allows you to introduce a new algorithm or new strategy without changing the code which uses that algorithm. For example, the Collections.sort() method which sorts the list of the object uses the Strategy pattern to compare objects. Since every object uses a different comparison strategy you can compare various objects differently without changing the sort method.
Method overloading in Java is an object-oriented programming concept that allows a programmer to declare two methods of the same name but with different method signatures, like a change in the argument list or a change in the type of argument. Original method :
public void show(String message){
System.out.println(message);
}
Overloaded method: number of arguments is different:
String is immutable while both StringBuffer and StringBuilder are mutable, which means any change e.g. converting String to upper case or trimming white space will produce another instance rather than changing the same instance. In later two, StringBuffer is synchronized while StringBuilder is not, in fact, it’s a ditto replacement of StringBuffer added in Java 1.5.
1. map里，hashmap无序的，想要有序的该怎么办？
HashMap
Bean 的生命周期概括起来就是 4 个阶段：