抽象类abstract

我们先来看一下Person类和子类的继承图，我们可以声明一个Person的父类，然后让它的子类派生，因为它的子类各有不同的属性和参数，所以为Person类实例方法显得有些浪费内存，这样，我们可以使用abstract关键字进行声明，这样就完全可以不需要实现这个方法了。

为了提高程序的清晰度，包含一个或多个抽象方法本身必须被声明为抽象的。

建议大家在抽象类中不要包含具体方法，尽量将通用的域和方法放在超类里。

抽象类不可悲被实例化，并且，继承他的子类必须实现父类的抽象方法定义。

package abstractClasses;

public class PersonTest {

	public static void main(String[] args) {
		Person[] people = new Person[2];
		
		people[0] = new Employee("Harry Hacker", 50000 , 1989, 10, 1);
		people[1] = new Student("Maria Morris", "computer science");
		
		for(Person p : people) {
			System.out.println(p.getName() + "," +p.getDescription());
		}
	}

}

package abstractClasses;

public abstract class Person {
	public abstract String getDescription();
	private String name;
	public Person(String name) {
		super();
		this.name = name;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	
	
}

package abstractClasses;
import java.time.*;
public class Employee extends Person {
	private double salary;
	private LocalDate hireDay;
	public Employee(String name, double salary, int year ,int month , int day) {
		super(name);
		this.salary = salary;
		this.hireDay = LocalDate.of(year, month, day);
	}
	public double getSalary() {
		return salary;
	}
	public void setSalary(double salary) {
		this.salary = salary;
	}
	public LocalDate getHireDay() {
		return hireDay;
	}
	public void setHireDay(LocalDate hireDay) {
		this.hireDay = hireDay;
	}
	@Override
	public String getDescription() {
		
		return String.format("an employee with a salary of $%.2f",salary);
	}
	
	public void raiseSalary(double byPercent) {
		double raise = salary * byPercent / 100;
		salary += raise;
	}
	
	
	
	
	
	
}

package abstractClasses;

public class Student extends Person {
	private String major;

	public Student(String name, String major) {
		super(name);
		this.major = major;
	}

	@Override
	public String getDescription() {
		// TODO Auto-generated method stub
		return "a student maroring in" + major;
	}	
}