Java Setter和Constructor的困惑 [英] Java Setter and Constructor confusion

问题描述

我对如何在Java中使用构造函数和设置器感到困惑，请参阅下面的示例代码：

I am a bit confused about how to use constructor and setter in Java, please see the sample code below:

public class Name {
   private String name;

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

public static void main(String[] args) {
    Name a=new Name();
    a.setName("123");       
    System.out.println(a.getName());
}

它打印出123，它使用的是setter方法而没有构造函数，我也写道下面的其他代码：

It prints out 123, it is using setter method without constructor, I also wrote the other code below:

public class Name {
   private String name;


   public Name(String nm){
      name=nm;
   }
   public String getName(){
      return name;
   }  
}



public static void main(String[] args) {
   Name a=new Name("123");

   System.out.println(a.getName());

}

这也打印出了123，它使用的是构造函数没有setter方法，这就是为什么我不明白构造函数和setter之间使用的区别是什么，请告诉我，加油！！

This one prints out 123 as well, it is using constructor without setter method, this is why I do not understand what the difference in using between constructor and setter, please advise, cheers!

推荐答案

如果要更改实例的 name 值，该怎么办。当然，您不会为此使用构造函数，因为它将创建一个新实例。在这种情况下，您将使用 setter 。

What if you want to change the value of name for an instance. Of course, you wouldn't use constructor for that, as it will create a new instance. You would use a setter in that case.

当然，如果要编写不可变类，那么您将不会提供任何设置者。实例字段中的任何修改都会创建一个新实例。

Of course, if you are writing an immutable class, then you wouldn't give any setters. Any modification in the instance fields, will create a new instance.

这里要了解的另一个重要点是，由于您在第二代码中提供了参数化构造函数，因此编译器不会添加任何默认构造函数。因此，第二类实际上没有任何0-arg构造函数。如果要稍后使用，则必须显式添加一个。

One more important point to understand here is, since you have provided a parameterized constructor in your 2nd code, the compiler wouldn't add any default constructor. So, the 2nd class doesn't actually have any 0-arg constructor. If you want to use it later on, then you have to add one explicitly.

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