子类实例到超类

Question

How do I create subclass objects, based on an superclass objects?

eg:

class Super {
    private int id;
    private String name;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

class Sub extends Super {
    private String lastName;

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }
}

public class Test {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        Super sup = new Super();
        sup.setId(1);
        sup.setName("Super");

        Sub sub = new Sub();

        System.out.println(sub.getName());
    }

}

How can I create a 'Sub' object with the properties of a 'Super' created earlier?

Or should I pass the properties manually, like:

sub.setName(sup.getName());
sub.setId(sup.getId());

Answer 1

you could add a copy constructor to Super Class

public class Super {
    private int id;
    private String name;

    public Super(String id, String name) {
        this.id = id;
        this.name = name;
    }

    public Super(Super other) {
        this.id = other.id;
        this.name = other.name;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

and then use this constructor in Sub class

class Sub extends Super {
    public Sub(Super other) {
        super(other);
    }

    private String lastName;

    public String getLastName() {
        return lastName;
    }

    public void setLastName(String lastName) {
        this.lastName = lastName;
    }
}

and you can call

Sub sub = new Sub(sup);

Answer 2

我会在Sub中创建一个静态方法：

Sub.fromSuper(Super s, String last)

Answer 3

I would use apache commons

BeanUtils.copyProperties(toBean, fromBean);

I wouldn't add a method to the class itself unless its really needed on every object. BeanUtils seem appropriate as it appears like something needed only in a specific situation.

In case that you really need the behaviour on every object, than implementing a copy constructor is a way to go