http://user.qzone.qq.com/1282179846/blog/1470248763
引入一個簡單的例子:
//Employee類 import java.util.*; public class Employee { private String name; private double salary; private Date hireday; public Employee(String n,double s,int year,int month,int day) { name =n; salary = s; GregorianCalendar calendar = new GregorianCalendar(year,month-1,day); hireday = calendar.getTime(); } public String getName() { return name; } public double getsalary() { return salary; } public Date gethireday() { return hireday; } public void raisesalary(double bypercent) { double raise = salary*bypercent/100; salary = salary + raise; } //public static void main(String[] args) { //Employee[] staff = new Employee[3]; //staff[0]=new Employee("diyige",75000,1987,12,25); //staff[1]=new Employee("dierge",50000,1989,10,1); //staff[2]= new Employee("disange",40000,1990,3,15); //for(Employee e : staff) //{ // e.raisesalary(5); //} //for(Employee e : staff) //{ // System.out.println("name="+e.getName()+",salary="+e.getsalary()+",hireday="+e.gethireday()); //} //} }
//manager類 public class Manager extends Employee{ private double bonus; public Manager(String n,double s,int year,int month,int day) { super(n,s,year,month,day); bonus = 0; } public void setbonus(double b) { bonus = b; } public double getsalary() { double basesalary = super.getsalary(); return basesalary+bonus; } //public static void main(String[] args) { //} }
//Testmanager public class Testmanager { public static void main(String[] args) { Manager boss = new Manager("bossa",80000,1987,12,15); boss.setbonus(5000); Employee[] staff = new Employee[3]; staff[0]=boss; staff[1]= new Employee("diyige",50000,1989,10,1); staff[2]= new Employee("dierge",40000,1990,3,15); for(Employee e : staff) { System.out.println("name="+e.getName()+",salary="+e.getsalary()); } } }
1/關鍵字extends表示繼承。表明正在構造一個新類派生於一個已經存在的類。已經存在的類稱為超類/基類/或者父類;新類稱為子類/派生類/或者孩子類。
子類擁有的功能比超類更加的豐富。(是一句廢話)
在設計的時候要將通用的方法放在超類中,將具有特殊用途的方法放在子類中。
2/子類要想訪問要想訪問超類中的方法需要使用特定的關鍵字super。例如:
public double getsalary() { double basesalary = super.getsalary(); return basesalary+bonus; }
在子類中可以增加域,增加方法,覆蓋超類的方法,然而絕對不能刪除集成的任何域和方法。
3/上面的代碼中,有:
public Manager(String n,double s,int year,int month,int day) { super(n,s,year,month,day); bonus = 0; }
其中
super(n,s,year,month,day);
的意思是調用超類中含有n,s,year,month,day參數的構造器。由於子類的構造器不能訪問超類中的私有域,所以必須利用超類中的構造器對這部分的私有域進行初始化,我們可以通過super實現對超類構造器的調用。
super調用構造器的語句必須是子類構造器的第一條語句。