该对象在通过构造函数传递后不会更改。为什么？

Question

您好，我有以下代码：

public class Dog {
    private String name;
    private int size;
    public Dog(String name, int size){
        this.name = name;
        this.size = size;
    }
    public void changeSize(int newSize){
        size = newSize;
    }
    public String toString(){
        return ("My name "+name+" my size "+ size);
    }
}

public class PlayWithDog {
    public PlayWithDog(Dog dog){
        dog = new Dog("Max", 12);
    }

    public void changeDogSize(int newSize, Dog dog){
        dog.changeSize(newSize);
    }


    public static void main(String[] args){
        Dog dog1 = new Dog("Charlie", 5);
        PlayWithDog letsPlay = new PlayWithDog(dog1); 
        System.out.println(dog1.toString()); // does not print Max.. Prints Charlie... .. Does not change... WHYYY???
        letsPlay.changeDogSize(8, dog1);
        System.out.println(dog1.toString()); // passing by value.. Expected Result... changes the size
        dog1 = new Dog("Max", 12);
        System.out.println(dog1.toString()); // Expected result again.. prints Max
    }
}

我知道 Java 总是按值传递所有内容。无论是原始类型还是对象。然而，在对象中，传递的是引用，这就是为什么您可以在通过方法传递对象后修改对象。我想测试当对象通过不同 class 的构造函数传递时是否同样适用。我发现对象没有改变。这对我来说似乎很奇怪，因为我只是在构造函数中传递对象的引用。它应该改变...?

Answer 1

I know Java always passes everything by value

这正是你的构造函数对传入的对象不做任何事情的原因。你可以改变传入对象的状态，但不能改变原始对象的引用多变的。

该对象在通过构造函数传递后不会更改。为什么？

The object does not change after being passed through a constructor. Why?

java

constructor

object

pass-by-reference

pass-by-value