我需要在
Java中克隆一个子类,但是在代码发生这种情况时,我不会知道子类类型,只知道超类.这样做的最佳设计模式是什么？
例：
class Foo {
String myFoo;
public Foo(){}
public Foo(Foo old) {
this.myFoo = old.myFoo;
}
}
class Bar extends Foo {
String myBar;
public Bar(){}
public Bar(Bar old) {
super(old); // copies myFoo
this.myBar = old.myBar;
}
}
class copier {
Foo foo;
public Foo makecopy(Foo oldFoo) {
// this doesn't work if oldFoo is actually an
// instance of Bar,because myBar is not copied
Foo newFoo = new Foo(oldFoo);
return newFoo;
// unfortunately,I can't predict what oldFoo's the actual class
// is,so I can't go:
// if (oldFoo instanceof Bar) { // copy Bar here }
}
}
解决方法
如果您可以控制要复制的类,那么虚拟方法就是前进的方法：
class Foo {
...
public Foo copy() {
return new Foo(this);
}
}
class Bar extends Foo {
...
@Override public Bar copy() {
return new Bar(this);
}
}
(理想情况下,使类成为抽象或有效的最终.)