Strings - Beginning Java 8 Fundamentals - page 384

String Objects Are Immutable
String objects are immutable. That is, you cannot modify the content of a String object. This leads to an advantage
that strings can be shared without worrying about them getting modified. For example, if you need two objects of
the String class with the identical content (the same sequence of characters), you can create one String object and
you can use its reference at both places. Sometimes the immutability of strings in Java is misunderstood, typically by
beginners. Consider the following piece of code:

String str;
str = new String("Just a string");
str = new String("Another string");

Here, str is a reference variable that can refer to any String object. In other words, str can be changed and it is
mutable. However, the String object, which str refers to, is always immutable. This scenario is depicted in Figure 11-1
and Figure 11-2 .

This is a String object, which is
immutable. You cannot change its
content.

Now, str is referring to a
String object in memory.

This is a reference variable and
can be changed.

str

str

Just a string

x

x

String str;

str = new String("Just a string");

Figure 11-1. A String reference variable and a String object

Now, str is referring to another
string object in memory

This is the string object, which is
immutable. You cannot change
its content

str

Another string

x

str= new String("Another string");

Figure 11-2. Assigning a different String object reference to a String variable