引用对象在java中是如何工作的

有人能让我明白吗？参考对象在java中如何工作从下面的代码我有object

r1

和reference object

r2

，

Rectangle r1=新矩形（）；矩形r2=r1
当我同时打印
r1
和
r2
时，输出是这样的
Rectangle@17f7bec4
（两者的输出相同）。好的，我知道这是内存地址，对吗？如果我打印下面的代码

  r1.length = 50;
  r2.length = 20;

  System.out.println("Value of R1's Length : " + r1.length);
  System.out.println("Value of R2's Length : " + r2.length);

  Rectangle r1 = new Rectangle();
  Rectangle r2 = r1;
  r2 = null;

 System.out.println("R1 : " + r1);
 System.out.println("R2 : " + r2);

上述代码的输出为：

R1长度值：20

R2的长度值：20

我无法理解此输出为什么两者都有
20
值？
如果这是因为引用内存，那么当我使用下面的代码时

  r1.length = 50;
  r2.length = 20;

  System.out.println("Value of R1's Length : " + r1.length);
  System.out.println("Value of R2's Length : " + r2.length);

  Rectangle r1 = new Rectangle();
  Rectangle r2 = r1;
  r2 = null;

 System.out.println("R1 : " + r1);
 System.out.println("R2 : " + r2);

两个对象的输出：

R1:
Rectangle@17f7bec4

R2:null

为什么r1没有
null
值？这就是让我困惑的点
下面是正在运行的代码

class Rectangle {
  double length;
  double breadth;
}

class RectangleDemo {
  public static void main(String args[]) {

  Rectangle r1 = new Rectangle();
  Rectangle r2 = r1;

r1.length = 50;
r2.length = 20;


  System.out.println("R1 : " + r1);
  System.out.println("Value of R1's Length : " + r1.length);
  System.out.println("Value of R2's Length : " + r2.length);
r2 = null;
  System.out.println("R2 : " + r2);

  }
}

r1
和
r2
是对对象的引用。在第一种情况下，它们都指向同一个对象，在第二种情况下，
r2
指向
null
。在代码中只有一个非空对象和两个引用


对代码的注释

Rectangle r1 = new Rectangle();    //object creation, make r1 point to created object
Rectangle r2 = r1;                 //r2 now points to the same object, that was created a line above

r1.length = 50;    //change lenght of object r1 points to
r2.length = 20;    //change lenght of object r2 points to (the same object as r1 points to)

r2 = null; //make r2 point to null

r1
和
r2
是对对象的引用。在第一种情况下，它们都指向同一个对象，在第二种情况下，
r2
指向
null
。在代码中只有一个非空对象和两个引用


对代码的注释

Rectangle r1 = new Rectangle();    //object creation, make r1 point to created object
Rectangle r2 = r1;                 //r2 now points to the same object, that was created a line above

r1.length = 50;    //change lenght of object r1 points to
r2.length = 20;    //change lenght of object r2 points to (the same object as r1 points to)

r2 = null; //make r2 point to null

对象是在堆中创建的，它有一个地址

Rectangle r1 = new Rectangle();
// r1 is pointing to that address
Rectangle r2 = r1;
// now r2 is pointing to the same address (same object) with r1
r2 = null;
// now r2 is null, but the object is still in the heap.
// r2 doesn't point to that object anymore.

您的对象是在堆中创建的，它有一个地址

Rectangle r1 = new Rectangle();
// r1 is pointing to that address
Rectangle r2 = r1;
// now r2 is pointing to the same address (same object) with r1
r2 = null;
// now r2 is null, but the object is still in the heap.
// r2 doesn't point to that object anymore.

它对任何语言都是一样的

Rectangle r1 = new Rectangle(); //r1 refers to this new Rectangle
Rectangle r2 = r1; //now r2 refers to the same Rectangle r1 refers to
r2 = null; //now is referring to null

您可以将r1设置为null，它将具有相同的行为

如果将r2更改为最终版本，则不允许更改

Rectangle r1 = new Rectangle();
final Rectangle r2 = r1; //now r2 will be forever referring to the Rectangle above even if you change r1 to null

检查一下，如果你把r1改为null，r2仍然会指向矩形。。。当你告诉r2=r1时。。。r2不是指向r1，r2实际上是指向矩形本身

Rectangle r1 = new Rectangle(2, 2);
final Rectangle r2 = r1; // now r2 will be forever referring to the
             // Rectangle above even if you change r1 to
             // null
r1 = null;
System.out.print(r2.getWidth());

输出宽度仍然为2，并且没有空错误。
对于任何语言，其工作方式相同

Rectangle r1 = new Rectangle(); //r1 refers to this new Rectangle
Rectangle r2 = r1; //now r2 refers to the same Rectangle r1 refers to
r2 = null; //now is referring to null

您可以将r1设置为null，它将具有相同的行为

如果将r2更改为最终版本，则不允许更改

Rectangle r1 = new Rectangle();
final Rectangle r2 = r1; //now r2 will be forever referring to the Rectangle above even if you change r1 to null

检查一下，如果你把r1改为null，r2仍然会指向矩形。。。当你告诉r2=r1时。。。r2不是指向r1，r2实际上是指向矩形本身

Rectangle r1 = new Rectangle(2, 2);
final Rectangle r2 = r1; // now r2 will be forever referring to the
             // Rectangle above even if you change r1 to
             // null
r1 = null;
System.out.print(r2.getWidth());

输出宽度仍然为2且没有空错误。
//现在r2为空，但对象仍在堆中。
确定！但当我将20赋给r2（r2.length=20；）时，为什么两者的值相同？对象仍在堆中将对象的长度设置为20后，您将r2分配给null。

//现在r2为null，但对象仍在堆中。确定！但当我将20赋给r2（r2.length=20；）时，为什么两者的值相同？在将对象的长度设置为20后，对象仍在您指定的r2为null的堆中