Immutability of the "String" class in Java

Consider the following code snippet:

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String a = "First";
System.out.println(a);
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The output is: First
Now, I use the string concatenation operator "+" as:

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String a = "First";
a = a + " Second"; //Creates a new String object
System.out.println(a);
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The output is: First Second

The string concatenation operator "+" implicitly creates a new String object and the reference to the old one is lost, thus the value of String object cannot be changed after it has been created (i.e. it's Immutable).