重构——以多态取代条件表达式（状态模式）

在写代码的时候，经常会遇到switch语句，根据状态码进行不同的操作，该方法简单，快捷，但维护起来较麻烦，也不易扩展。      例如，如下代码

public class Employee {
    private int mType;
    static final int salary=500;
    static final int commission=500;
    static final int bonus=1000;
    
    static final int ENGINEER=0;
    static final int SALESMAN=1;
    static final int MANAGER=2;
    
    public Employee(int type) {
    	this.mType=type;
	}
    

    
    int payAmout(){
    	switch (mType) {
		case ENGINEER:
			    return salary;
		case SALESMAN:
			  return salary+commission;
		case MANAGER:
			  return salary+bonus;
		default:
			throw new RuntimeException();
		}
    }
}

 

该类有Employee类，并且区分了三种状态：ENGINEER、SALESMAN、MANAGER。运行代码如下所示

public class Main {
   public static void main(String[] args) {
	Employee enginer=new Employee(Emplo