Question

I try to get a reference to an element of an ArrayList but I fail.

ArrayList<String> test = new ArrayList<String>();

test.add("zero");
test.add("one");
test.add("two");

 String s1 = test.get(1);
 String s2 = test.get(1);

 System.out.println(test.get(1) +" " + s1 + " " + s2);

 s1 += " modificated";

 System.out.println(test.get(1) +" " + s1 + " " + s2);

Any suggestions?

Answer 1

You can’t do this in Java. All you’re doing is fetching the value from the ArrayList. That value is a reference, but it’s a reference in Java terminology, which isn’t quite the same as in C++.

That reference value is copied to s1, which is thereafter completely independent of the value in the ArrayList. When you change the value of s1 to refer to a new string in this line:

s1 += "modificated";

that doesn’t change the value in the ArrayList at all.

Now if you were using a mutable type such as StringBuilder, you could use:

StringBuilder builder = list.get(0);
builder.append("more text");
System.out.println(list.get(0)); // Would include "more text"

Here you’re not changing the value in the ArrayList – which is still just a reference – but you’re changing the data within the object that the value refers to.