java - 我们可以在抽象装饰器中将装饰对象的实例设为私有(private)而不是保护吗？

Question

我注意到大多数示例对正在装饰的实例使用 protected。我也可以使用 private 吗？

public abstract class CoffeeDecorator implements Coffee {
    protected Coffee decoratedCoffee;

    public CoffeeDecorator(Coffee c) {
        this.decoratedCoffee = c;
    }
    // ...
}

Answer 1

装饰器模式用作继承的替代方案，有助于添加类的附加功能，而无需修改或扩展它本身。

我会用 private 属性而不是 abstract 类来装饰它。在一个非常简单的示例中进行演示:

CupOfCoffee.java

final class CupOfCoffee implements Coffee {

    public final String prepareCoffee() {
        return "Coffee";
    }
}

糖咖啡.java

final class SugarCoffee implements Coffee {

    private final Coffee coffee;

    public SugarCoffee(final Coffee coffee) {
        this.coffee = coffee;
    }

    public final String prepareCoffee() {
        return coffee.prepareCoffee() + " with sugar";
    }
}

牛奶咖啡.java

final class MilkCoffee implements Coffee {

    private final Coffee coffee;

    public MilkCoffee(final Coffee coffee) {
        this.coffee = coffee;
    }

    public final String prepareCoffee() {
        return coffee.prepareCoffee() + " with milk";
    }
}

使用可组合垂直装饰器的演示:

new MilkCoffee(
    new SugarCoffee(
        new SugarCoffee(
            new Coffee()
        )
    )
).prepareCoffee()           // Coffee with sugar with sugar with milk