Defensive copying of Number subclass

Please consider the following example:

public final class ImmutableWrapper<T extends Number> {

    private final T value;

    public ImmutableWrapper(T value) {
        // a subclass of Number may be mutable
        // so, how to defensively copying the value?
        this.value = value;
    }

    public T getValue() {
        // the same here: how to return a copy?
        return value;
    }
}

In order to make this class immutable, I must defensively copy any mutable parameter passed to the constructor and create copies of internal mutable objects returned by public methods.

Is this possible? If not, is there any workaround?

---

Since all Number s are Serializable you can create copies by serializing/deserializing them.

Maybe you can use apache commons-lang's SerializationUtils.clone(Serializable) .

public final class ImmutableWrapper<T extends Number> {

    private final T value;

    public ImmutableWrapper(T value) {
        // a subclass of Number may be mutable
        // so, how to defensively copying the value?
        this.value = SerializationUtils.clone(value);
    }

    public T getValue() {
        // the same here: how to return a copy?
        return  SerializationUtils.clone(value);
    }
}

or if you want to implement it by yourself take a look at:

Cloning of Serializable and Non-Serializable Java Objects

---

You need to clone the object. So your code would look like:

public final class ImmutableWrapper<T extends Number> {
    private final T value;

    public ImmutableWrapper(T value) {
        this.value = value.clone();
    }

    public T getValue() {
        return value.clone();
    }
}

链接地址: http://www.djcxy.com/p/18998.html

上一篇: 网址不适用于某些曲目

下一篇: Number子类的防御性复制