Setting equal in Java: by value or reference?

Question

I did two tests, the first starting with Strings

    String str1 = \"old\";
    String str2 = str1;
    str1 = \"new\";

    System.out.println(         


        

Answer 1

Your difference is here

str1 = "new";

vs

list1.add(1);

In the String example, you are changing references. Changing the reference of str1 does not affect any other variables.

In the List example, you are invoking a method, which dereferences the reference and accesses the object. Any variables referencing that same object will see that change.

Here it is

List list1 = new ArrayList(); // 1
List list2 = list1; // 2 
list1.add(1); // 3

looks like this

   1:  list1 ===> object1234
   2:  list1 ===> object1234 <=== list2
   3:  list1 ===> object1234 (internal modification) <=== list2