英文:
Given a mutable class, how to make immutable a specific object of this class?
问题
我有这个类，显然对于我创建的每个实例都是可变的，但我想知道是否有一种包装器（或类似的东西）可以使得只有一个特定的这个类的对象是不可变的。例如 Collections.unmodifiableList(beanList)。
class Animal {
private String name;
private String commentary;
public Animal(String nombre, String comentario) {
this.name = nombre;
this.commentary = comentario;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
Animal animal = (Animal) o;
return Objects.equals(name, animal.name);
}
@Override
public int hashCode() {
return Objects.hash(name);
}
public String getName() {
return name;
}
public String getCommentary() {
return commentary;
}
// 此处省略了setCommentary和setName方法，以及其他方法
}
英文:
I got THIS class which is obviously mutable for every instance I create, but I want to know if there´s
some kind of wrapper (or something) to make just ONE specific object of THIS class immutable. e.g Collections.unmodifiableList(beanList).
class Animal {
private String name;
private String commentary;
public Animal(String nombre, String comentario) {
this.name = nombre;
this.commentary = comentario;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
Animal animal = (Animal) o;
return Objects.equals(name, animal.name);
}
@Override
public int hashCode() {
return Objects.hash(name);
}
public String getName() {
return name;
}
public String getCommentary() {
return commentary;
}
public void setCommentary(String commentary) {
this.commentary = commentary;
}
public void setName(String name) {
this.name = name;
}
}
答案1
得分: 6
我所知道的唯一方法是实例化它并重写能够修改特定实例的方法：
Animal animal = new Animal("name", "commentary") {
@Override
public void setCommentary(String commentary) {
throw new UnsupportedOperationException("The Animal is immutable");
}
@Override
public void setName(String name) {
throw new UnsupportedOperationException("The Animal is immutable");
}
};
这也满足了只有 类的一个特定实例 具有特殊行为的条件。
如果你需要更多类似的实例，可以创建一个充当装饰者（并非完全如此）的包装类。不要忘记 将这个类声明为 final，否则你可能会按照我上面描述的方式重写它的方法，从而破坏其不可变性。
Animal animal = new ImmutableAnimal(new Animal("name", "commentary"));
final class ImmutableAnimal extends Animal {
public ImmutableAnimal(Animal animal) {
super(animal.getName(), animal.getCommentary());
}
@Override
public void setCommentary(String commentary) {
throw new UnsupportedOperationException("The Animal is immutable");
}
@Override
public void setName(String name) {
throw new UnsupportedOperationException("The Animal is immutable");
}
}
英文:
The only way I am aware of is to instantiate it and override the methods that are able to modify the particular instance:
Animal animal = new Animal("name", "commentary") {
@Override
public void setCommentary(String commentary) {
throw new UnsupportedOperationException("The Animal is immutable");
}
@Override
public void setName(String name) {
throw new UnsupportedOperationException("The Animal is immutable");
}
};
This also satisfied the condition that only one specific instance of the class has a special behavior.
If you need more of them, create a wrapping class that acts as a decorator (isn't exactly). Do not forget to make the class as final otherwise you would be able to override its method in the way I described above and its immutability might break.
Animal animal = new ImmutableAnimal(new Animal("name", "commentary"));
final class ImmutableAnimal extends Animal {
public ImmutableAnimal(Animal animal) {
super(animal.getName(), animal.getCommentary());
}
@Override
public void setCommentary(String commentary) {
throw new UnsupportedOperationException("The Animal is immutable");
}
@Override
public void setName(String name) {
throw new UnsupportedOperationException("The Animal is immutable");
}
}
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