Why does appending “” to a String save memory?

Question

I used a variable with a lot of data in it, say String data. I wanted to use a small part of this string in the following way:

this.smallpart =          


        

Answer 1

Firstly, calling java.lang.String.substring creates new window on the original String with usage of the offset and length instead of copying the significant part of underlying array.

If we take a closer look at the substring method we will notice a string constructor call String(int, int, char[]) and passing it whole char[] that represents the string. That means the substring will occupy as much amount of memory as the original string.

Ok, but why + "" results in demand for less memory than without it??

Doing a + on strings is implemented via StringBuilder.append method call. Look at the implementation of this method in AbstractStringBuilder class will tell us that it finally do arraycopy with the part we just really need (the substring).

Any other workaround??

this.smallpart = new String(data.substring(12,18));
this.smallpart = data.substring(12,18).intern();