inheritance super overrides printMethod in Superclass override重写父方法

Core Java Web Page http://horstmann.com/corejava.html

[

　　inheritance 

]

package v1ch05.inheritance;

import java.time.LocalDate;

public class Employee {

    private String name;
    private double salary;
    private LocalDate hireDay;

    public Employee(String name, double salary, int year, int month, int day) {
        this.name = name;
        this.salary = salary;
        hireDay = LocalDate.of(year, month, day);
    }

    public String getName() {
        return name;
    }

    public double getSalaary() {
        return salary;
    }

    public LocalDate getHireDay() {
        return hireDay;
    }

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

 

package v1ch05.inheritance;

public class Manager extends Employee {
    private double bouns;

    public Manager(String name, double salary, int year, int month, int day) {
        super(name, salary, year, month, day);
        bouns = 0;
    }

    public double getSalary() {
        double baseSalary = super.getSalaary();
        return baseSalary + bouns;
    }

    public void setBouns(double b){
        bouns = b;
    }
}

 

package v1ch05.inheritance;

public class ManagerTest {
    public static void main(String[] args) {
        // construct a Manager object
        Manager boss = new Manager("Carl Cracker", 80000, 1987, 12, 15);
        boss.setBouns(5000);

        Employee[] staff = new Employee[3];

        // fill the staff array qwith Manager and Employee objects
        staff[0] = boss;
        staff[1] = new Employee("harry Hacker", 5000, 1989, 10, 1);
        staff[2] = new Employee("Tommy Tester", 40000, 1990, 3, 15);

        // print out information about all Emplyee objects
        for (Employee e : staff)
            System.out.println("name=" + e.getName() + ",salary=" + e.getSalaary() + "");
    }
}

 

 

super

Using the Keyword super (The Java™ Tutorials > Learning the Java Language > Interfaces and Inheritance) https://docs.oracle.com/javase/tutorial/java/IandI/super.html

 

Using the Keyword super

Accessing Superclass Members

If your method overrides one of its superclass's methods, you can invoke the overridden method through the use of the keyword super. You can also use super to refer to a hidden field (although hiding fields is discouraged). Consider this class, Superclass:

public class Superclass {

    public void printMethod() {
        System.out.println("Printed in Superclass.");
    }
}

Here is a subclass, called Subclass, that overrides printMethod():

public class Subclass extends Superclass {

    // overrides printMethod in Superclass
    public void printMethod() {
        super.printMethod();
        System.out.println("Printed in Subclass");
    }
    public static void main(String[] args) {
        Subclass s = new Subclass();
        s.printMethod();    
    }
}

Within Subclass, the simple name printMethod() refers to the one declared in Subclass, which overrides the one in Superclass. So, to refer to printMethod() inherited from Superclass, Subclass must use a qualified name, using super as shown. Compiling and executing Subclass prints the following:

Printed in Superclass.
Printed in Subclass

Subclass Constructors

The following example illustrates how to use the super keyword to invoke a superclass's constructor. Recall from the Bicycle example that MountainBike is a subclass of Bicycle. Here is the MountainBike (subclass) constructor that calls the superclass constructor and then adds initialization code of its own:

public MountainBike(int startHeight, 
                    int startCadence,
                    int startSpeed,
                    int startGear) {
    super(startCadence, startSpeed, startGear);
    seatHeight = startHeight;
}   

Invocation of a superclass constructor must be the first line in the subclass constructor.

The syntax for calling a superclass constructor is

super();  

or:

super(parameter list);

With super(), the superclass no-argument constructor is called. With super(parameter list), the superclass constructor with a matching parameter list is called.

---

Note: If a constructor does not explicitly invoke a superclass constructor, the Java compiler automatically inserts a call to the no-argument constructor of the superclass. If the super class does not have a no-argument constructor, you will get a compile-time error.Object does have such a constructor, so if Object is the only superclass, there is no problem.

---

If a subclass constructor invokes a constructor of its superclass, either explicitly or implicitly, you might think that there will be a whole chain of constructors called, all the way back to the constructor of Object. In fact, this is the case. It is called constructor chaining, and you need to be aware of it when there is a long line of class descent.

« Previous • Trail • Next »