Review-Java基础--抽象类(abstract)

抽象类不能被实例化，即如果将一个类声明为abstract，就不能创建这个类的对象。但可以创建一个具体的子类的对象。

另外：可以根据抽象类，可以定义一个抽象类的对象变量，但它只能引用非抽象子类的对象。

假设Person为一个抽象类，Sudent为一个继承自Person的非抽象子类。则Person p=new Person(“name”);当然了这事一个错误的写法

但可以创建一个具体子类的对象

Person p=new Student(“name”);

p为抽象类Person的变量，Person引用了一个非抽象子类Student的实例

package abstractClassess;

import javax.swing.text.StyledEditorKit.ForegroundAction;

/**
* This program demonstracts abstract classes;
*
* @version 2016-08-29
* @author Administrator
*
*/
public class PersonTest {

public static void main(String[] args) {
Person[] person = new Person[2];
//抽象类不能实例化
person[0] = new Employee("张三", 3728, 1293, 20, 2);
person[1] = new Student("小明", "Computer Science And Technology");
for (Person people : person) {
System.out.println(people.getName() + "," + people.getDescription());
}
}

}

package abstractClassess;

public abstract class Person {

/* 抽象方法充当占位作用，具体实现在子类中*/
public abstract String getDescription();

private String name;

public Person(String name)
{
this.name=name;
}
public String getName()
{
return name;
}

}

package abstractClassess;

public class Student extends Person{

private String major;
public Student(String name,String major){
super(name);

this.major=major;
}
public String getDescription()
{
return ("a student majoring in "+major);
}
}

package abstractClassess;

import java.util.Date;
import java.util.GregorianCalendar;

public class Employee extends Person{

private double salary;
private Date hireDay;
public Employee(String name,double s,int year,int month,int day) {
super(name);
// TODO Auto-generated constructor stub
this.salary=s;
GregorianCalendar calender=new GregorianCalendar(year,month-1,day);
hireDay=calender.getTime();

}

public double getSalary()
{
return salary;
}
public Date getHireDay()
{
return hireDay;
}
@Override
public String getDescription() {
// TODO Auto-generated method stub
return String.format("an employee with a salary of $%.2f", salary);
}

public void raiseSalary(double byPercent)
{
double raise=salary * byPercent/100;
salary+=raise;
}
}