4.如何在一个实体类中注入另一个实体类

实体类Person

public class Person {
    private String name;
    private int age;
    //类的关联关系 ...关联,继承
    //Pet pet = new Pet();耦合
    private Pet pet;
    public Person(String name, int age, Pet pet) {
        super();
        this.name = name;
        this.age = age;
        this.pet = pet;
    }
    public Person() {
        super();
        // TODO Auto-generated constructor stub
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public Pet getPet() {
        return pet;
    }
    public void setPet(Pet pet) {
        this.pet = pet;
    }
    @Override
    public String toString() {
        return "Person [name=" + name + ", age=" + age + ", pet=" + pet + "]";
    }
    
    
}

实体类Pet

public class Pet {
    private String petName;
    private int age;
    public String getPetName() {
        return petName;
    }
    public void setPetName(String petName) {
        this.petName = petName;
    }
    public int getAge() {
        return age;
    }
    public void setAge(int age) {
        this.age = age;
    }
    @Override
    public String toString() {
        return "Pet [petName=" + petName + ", age=" + age + "]";
    }
    
    
}

可以看到在Person类中,有Pet pet 这样一个属性,那么如何给它注入属性?
可以通过ref标签

ref标签 引用或指定
1.ref="pet1" 第一种写法.
2.

也可以:

还可以通过一种更为复杂的方式: