带有Java组合的Setters和getter

Question

对于Java中的setter和getters，我对它何时使用组合而不是继承有疑问。这个疑问是在我解决大学作业的时候提出的。

假设我有两门课:汽车和电池。电池有3个变量(var1、var2、var3)和getter和setter。

汽车课程是这样的：

public class Car {
  private String color;
  private String model;
  private Battery battery;

  public Car(String color, String model, Battery battery) {
    this.color = color;
    this.model = model;
    this.Battery = new Battery(battery);
  }

  public getBattery() {
    return new Battery(battery);
  }

  public void setBattery(Battery battery) {
    this.battery = new Battery(battery.getVar1(), battery.getVar2(), battery.getVar3());
    //or this.battery = battery;
  }

我知道getter方法的推理(因为它与对象的引用相关)，但是setter方法呢？我试着在Udemy (来自Tim )的Java课程中查找网页，但我还没有看到这个地址。

有人能帮帮我吗？谢谢!

Answer 1

Car类中的三个方法中的每一个都是Battery的防御拷贝。这可以防止Car之外的任何其他对象更改Car中的Battery，因为没有其他对象会引用该特定的Battery实例(因为它总是被复制)。

习语new Battery(battery)被称为复制构造函数，因为它利用构造函数克隆对象。这是防御性复制的一个共同属性。

Answer 2

就其实现方式而言，我不同意这种格式。更好的做法是编写this.battery = leave并将其保留在这个位置(而不是像问题中那样创建一个新对象并分配它的变量)。

Answer 3

在某些地方，您的代码看起来很奇怪，我已经将它更改为我所期望的样子：

public class Car {
  private String color;
  private String model;
  private Battery battery;

  public Car(String color, String model, Battery battery) {
    this.color = color;
    this.model = model;

    //Now, we're setting Car.battery to the battery that you passed in. 
    //Previously, you were passing the battery instance back into the Battery constructor.
    this.battery = battery;
    //this.battery = new Battery(battery); 
  }

  public getBattery() {
    //We want to return the battery we have above, not a new battery
    return battery;
    //return new Battery(battery);
  }

  public void setBattery(Battery battery) {
    //You wouldn't do this. Just use the line you've commented out.
    //No need to remake a new Battery object when you already have one passed in.

    this.battery = new Battery(battery.getVar1(), battery.getVar2(), battery.getVar3());
    //or this.battery = battery;
  }

setter方法的意义是什么？它是在您已经建造了汽车之后，在汽车实例中设置/更改电池的值。而在构造过程中使用构造函数来设置电池。