Java对象创建后如何修改关联Third类的name字段无需新建实例

你已经完成First、Second、Third三个关联类的定义与实例绑定，当前关联的Third实例name字段值为john，需要在不创建新Third类对象的前提下，将该字段值修改为sam。

First类 #

public class First {
    List<Second> second;

    public List<Second> getSecond() {
        return second;
    }

    public void setSecond(List<Second> second) {
        this.second = second;
    }
}

Second类 #

public class Second {
    protected Third third;

    public Third getThird() {
        return third;
    }

    public void setThird(Third third) {
        this.third = third;
    }
}

Third类 #

public class Third {
    protected String name;

    public String getName() {
        return name;
    }

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

    @Override
    public String toString() {
        return "Third{" +
                "name='" + name + '\'' +
                '}';
    }
}

Third类已经提供了public的setName setter方法用于修改name属性，不需要新建Third实例，直接获取已有的Third实例调用该方法赋值即可，有两种实现方式：

• 方式一：直接使用main方法中已声明的third变量修改

  third.setName("sam");
  

• 方式二：如果未直接持有third变量，从顶层First实例逐层获取关联对象后修改（符合Java封装规范，推荐）

  first.getSecond().get(0).getThird().setName("sam");
  

import java.util.ArrayList;
import java.util.List;

public class Test {
    public static void main(String[] args) {
        Third third = new Third();
        third.setName("john");

        Second second = new Second();
        List<Second> list = new ArrayList<>();
        list.add(second);
        second.setThird(third);
        First first = new First();
        first.setSecond(list);
        // 修改name为sam，以下两种写法二选一即可
        // 写法1
        third.setName("sam");
        // 写法2
        // first.getSecond().get(0).getThird().setName("sam");

        System.out.println(first.getSecond().get(0).getThird().toString());
    }
}

运行后输出结果为：Third{name='sam'}，修改生效。

内容的提问来源于stack exchange，提问作者Saurabh Kumar Singh