组合Aggregation / Composition

定义

什么是

一个类内使用另外一个类作为属性

表达含义

有

名词

组合 / 聚合

Composition / Aggregation

组合解决代码重用

基本方案

Animal.java
1 2 3 4 5 6 
public class Animal {    public int age;    public void eat() {        System.out.println("Animal eat()");    }}

Person.java
1 2+3-4 5-6-7-8 9 10 11 
public class Person {    public Animal animal;    public int age;    public double balance;    public void eat() {        System.out.println("Person eat()");    }    public void work() {        System.out.println("Person work()");    }}

Dog.java
1 2+3-4-5-6-7 8 9 10 
public class Dog {    public Animal animal;    public int age;    public void eat() {        System.out.println("Dog eat()");    }    public void bark() {        System.out.println("Dog bark()");    }}

Zoo.java
1 2 3 4 5 6 7 8 9 10 11 
public class Zoo {    public static void main(String[] args) {        new Zoo().run();    }     public void run() {        Dog dog = new Dog();        dog.animal = new Animal();        dog.animal.eat();    }}

封装

Person.java
1 2*3 4 5+6+7+8 9+10+11+12 13 14 15 
public class Person {    private Animal animal;    public double balance;     public Person() {        animal = new Animal();    }     public void eat() {        animal.eat();    }    public void work() {        System.out.println("Person work()");    }}

Zoo.java
1 2 3 4 5 6 7 8-9*10 11 
public class Zoo {    public static void main(String[] args) {        new Zoo().run();    }     public void run() {        Dog dog = new Dog();        dog.animal = new Animal();        dog.eat();    }}

差异化

Person.java
1 2 3 4 5 6 7 8 9 10 11+12 13 14 15 16 
public class Person {    private Animal animal;    public double balance;     public Person() {        animal = new Animal();    }     public void eat() {        animal.eat();        System.out.println("Person eat()");    }    public void work() {        System.out.println("Person work()");    }}