在Java中 ‘is a relationship’ 与‘Has a relationship’的区别

最新推荐文章于 2023-11-27 10:22:21 发布

最新推荐文章于 2023-11-27 10:22:21 发布 · 821 阅读

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#Java #Google

本文解析了面向对象编程中'is-a'与'has-a'关系的概念，通过继承与组合的方式实现了代码复用。举例说明了House作为Building的子类体现了'is-a'关系，而House包含Bathroom则体现了'has-a'关系。

今天在SCJP的试题中看见关于‘is a relationship’ ，‘has a relationship’的试题，一开始没搞清楚怎么回事，就google了一下，找到如下文章，觉得挺有用的。跟大家分享下啊。

what is 'is a' and 'has a' relationship:

The ‘is a relationship’ is expressed with inheritance and ‘has a relationship’ is expressed with composition.
Both inheritance and composition allow you to place sub-objects inside your new class. Two of the main techniques for code reuse are class inheritance and object composition.

e.g.,

is a --- House is a Building

class Building {

.......
}

class House extends Building {

.........
}

has a -- House has a bathroom

class House
{
Bathroom room = new Bathroom() ;
....
public void getTotMirrors()
{
room.getNoMirrors();
....
}
}
Inheritance Vs Composition

Inheritance is uni-directional. For example House is a Building. But Building is not a House. Inheritance uses
‘extends’ key word. Composition: is used when House has a Bathroom. It is incorrect to say House is a Bathroom.

Composition simply means using instance variables that refer to other objects. The class House will have an instance variable, which refers to a Bathroom object.