在父类之间来回转换后，子对象是否会丢失其唯一属性？

Question

考虑以下类别：

public class Phone {
    private boolean has3g;

    public boolean has3g() {
        return has3g;
    }

    public void setHas3g(boolean newVal) {
        has3g = newVal;
    }
}

public class Blackberry extends Phone {
    private boolean hasKeyboard;

    public boolean hasKeyboard() {
        return hasKeyboard;
    }

    public void setHasKeyboard(boolean newVal) {
        hasKeyboard = newVal;
    }
}

如果我要创建的实例Blackberry，则将其强制转换为Phone对象，然后再强制转换为Blackberry，原始Blackberry对象会丢失其成员变量吗？例如：

Blackbery blackbery = new Blackberry();
blackbery.setHasKeyboard(true);

Phone phone = (Phone)blackbery;

Blackberry blackberry2 = (Blackberry)phone;

// would blackberry2 still contain its original hasKeyboard value?
boolean hasKeyBoard = blackberry2.hasKeyboard();

Answer 1

强制转换完全不会改变基础对象-只是向编译器发送一条消息，可以将A视为B。

也不必将if 强制A转换为Bif A extends B，即不需要将子类型强制转换为其超类型；如果是从超类型到子类型的，则只需要强制类型转换