Question

What I read about strings is when a string object is created in Java it is immutable. For example:

String s=new String();
s="abc";
s="xyz";

Does the String s no longer point to "abc"?

And another thing: what is size of s;
Is the String object analogous to a char* pointer in C in terms of the memory model?

Answer 1

Yes, Strings in Java are immutable. That is to say, the content pointed too by a string variable cannot be changed after it has been initialized. Using your own examples to illustrate:

String s=new String();

In the above code, you have created a new, empty String and assigned it to the s variable.

s="abc";

You have created another new String, this time with content “abc”. You have set the variable s to point to this new String. Your previous, empty string will get garbage collected at some point in the future.

s="xyz";

Similar to above. You have created another new String, with content “xyz”, and set the variable s to point to it. The previous “abc” string will get garbage collected at some point in the future.

Note that at no point did you actually modify the empty string to become “abc”, or modify the “abc” string to become “xyz”. All operations on String that concatenate, convert case, or otherwise appear to modify the String actually return a new String with the function results. To illustrate:

String s = new String("Hello");
String b = s.concat(" World");
System.out.println(s); // This will NOT produce 'Hello World'

System.out.println(b); // Whereas, this will

As to the last part of your question, you would use the length() function to determine the ‘size’ of your string. Note that this is based on Unicode encoding, and might not be what you expect the length to be as defined in ANSI C.