抽象类abstract

冷不防 2022-05-19 05:49 164阅读 0赞

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。

![70][]

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;
    	}	
    }

[70]: /images/20220519/ab7644b23f4d4975948b8477cf43ac14.png