10. 类的关系——关联关系

1、类的四种关系

· 关联关系

· 依赖关系

· 继承关系

· 实现关系（本质也是继承关系）

2、关联关系

在关联关系中，没有新的语法和概念，不过是一种思想。

对象和对象之间的连接。在Java中，关联关系的代码表现形式为一个类做为另一个类的属性类型存在。即语义上是“有”的关系：”has-a”。

2.1 按整体和部分分类：

（1）组合——同生共死

（2）聚合——不同生不同死

区别：生命周期不同

例：组合——同生同死

   创建整体时部分也同时创建，整体销毁部分也销毁

//组合（同生同死）

//人类
public class People {
    private String name;
    private String age;
    private Phone[] phones;
    
    public People() {
        phones = new Phone[3];
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getAge() {
        return age;
    }

    public void setAge(String age) {
        this.age = age;
    }

    public Phone[] getPhones() {
        return phones;
    }

    public void setPhones(Phone[] phones) {
        this.phones = phones;
    }

    @Override
    public String toString() {
        return "People [name=" + name + ", age=" + age + ", phones=" + Arrays.toString(phones) + "]";
    }
    
    
}

//电话类
public class Phone {
    private String color;
    private String num;
    
    public Phone() {
        // TODO Auto-generated constructor stub
    }

    public String getColor() {
        return color;
    }

    public void setColor(String color) {
        this.color = color;
    }

    public String getNum() {
        return num;
    }

    public void setNum(String num) {
        this.num = num;
    }

    @Override
    public String toString() {
        return "Phone [color=" + color + ", num=" + num + "]";
    }
    
    
}

//测试
public class Client {
    public static void main(String[] args) {
        People people = new People();
        people = null;
        System.out.println(people.getPhones());
    }
}

结果：

image.png

例：聚合——不同死不同

创建整体时部分可以不创建，整体消亡时部分还存在。

///聚合（不同生不同死）

//人类
public class People {
    private String name;
    private String age;
    private Phone[] phones;
    
    public People() {
        // TODO Auto-generated constructor stub
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getAge() {
        return age;
    }

    public void setAge(String age) {
        this.age = age;
    }

    public Phone[] getPhones() {
        return phones;
    }

    public void setPhones(Phone[] phones) {
        this.phones = phones;
    }

//电话类
public class Phone {
    
    private String color;
    private String num;
    
    public Phone() {
        // TODO Auto-generated constructor stub
    }

    public String getColor() {
        return color;
    }

    public void setColor(String color) {
        this.color = color;
    }

    public String getNum() {
        return num;
    }

    public void setNum(String num) {
        this.num = num;
    }

    @Override
    public String toString() {
        return "Phone [color=" + color + ", num=" + num + "]";
    }
}

//测试类
public class Client {
    public Client() {
        // TODO Auto-generated constructor stub
    }
    
    public static void main(String[] args) {
        People people = new People();
        Phone[] phones = new Phone[3];
        
        
        people.setPhones(phones);
        
        people = null ; 
        System.out.println(phones);
        System.out.println(people.getPhones());
        
    }
}

结果：

image.png

2.2 按方向分类：

（1）单向关联：A类关联B类

（2）双向关联：A关联B，B也关联A

例：单向关联

//类： 电话
public class Phone {

    // 属性：型号
    private String type;

    // 属性：颜色
    private String color;

    // 属性：品牌
    private String brand;

    // 构造方法
    public Phone() {

    }

    // Getters and Setters
    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public String getColor() {
        return color;
    }

    public void setColor(String color) {
        this.color = color;
    }

    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }

}

//类：人
public class Person {

    // 属性：电话
    private Phone phone;

    // 构造方法：默认的
    public Person() {

    }

    // Getters and Setters
    public Phone getPhone() {
        return phone;
    }

    public void setPhone(Phone phone) {
        this.phone = phone;
    }

}

例：双向关联

//类： 电话
public class Phone {

    // 属性：型号
    private String type;

    // 属性：颜色
    private String color;

    // 属性：品牌
    private String brand;

    // 属性：所有者
    private Person owner;

    // 构造方法：默认的
    public Phone() {

    }

    // Getters and Setters
    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public String getColor() {
        return color;
    }

    public void setColor(String color) {
        this.color = color;
    }

    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }

    public Person getOwner() {
        return owner;
    }

    public void setOwner(Person owner) {
        this.owner = owner;
    }

}

//类：人
public class Person {

    private Phone phone;

    public Person() {
        
    }

    public Phone getPhone() {
        return phone;
    }

    public void setPhone(Phone phone) {
        this.phone = phone;
    }

}

2.3按多重性分类：

（1）一对一

（2）一对多

例：一对一

//类： 电话
public class Phone {

    // 属性：型号
    private String type;

    // 属性：颜色
    private String color;

    // 属性：品牌
    private String brand;

    // 构造方法：默认的
    public Phone() {

    }

    // Getters and Setters
    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public String getColor() {
        return color;
    }

    public void setColor(String color) {
        this.color = color;
    }

    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }

}

//类：人
public class Person {

    private Phone phone;

    public Person() {
        
    }

    public Phone getPhone() {
        return phone;
    }

    public void setPhone(Phone phone) {
        this.phone = phone;
    }

}

例：一对多

//类： 电话
public class Phone {

    // 属性：型号
    private String type;

    // 属性：颜色
    private String color;

    // 属性：品牌
    private String brand;

    // 构造方法
    public Phone() {

    }

    // Getters and Setters
    public String getType() {
        return type;
    }

    public void setType(String type) {
        this.type = type;
    }

    public String getColor() {
        return color;
    }

    public void setColor(String color) {
        this.color = color;
    }

    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }

}


//类：人
public class Person {
    
    //数组
    private Phone[]  phones0 ;

    //集合
    private List<Phone> phones;

    private Set<Phone> phones2;

    private Map<String, Phone> phone3;

    public Person() {
        
        this.phones0 = new Phone[3];

        phones = new ArrayList<Phone>();

    }

}