Strings again

Strings have been with you since module 2: nextLine() reads one, + joins them, and println prints them. You've compared them with equals (module 6) and built them up in a loop with += (module 11). This module is about what else you can do with text: look at its characters, cut out pieces, and split a line into parts. That's how a program makes sense of input such as Aino,42.

Methods of a String

A String has methods of its own. You call them with a dot after the string, the same way you call nextLine() on a scanner. length() tells how many characters the string has:

Scanner scanner = new Scanner(System.in);
System.out.println("Name of your pet?");
String pet = scanner.nextLine();
System.out.println(pet + " has " + pet.length() + " characters");

Mr Biscuit

Name of your pet?
Mr Biscuit has 10 characters

Every character counts, the space included. The empty string "", which is what nextLine() gives when the user presses Enter without typing anything, has the length 0. isEmpty() is true for it, and false for any other string.

Strings can't be changed

toUpperCase(), toLowerCase() and trim() look as if they change a string, but they don't: each one gives back a new string. trim() removes the spaces at the start and at the end, not the ones in the middle. The brackets show where the spaces are:

String title = "  Tea Time ";
System.out.println("[" + title.toUpperCase() + "]");
System.out.println("[" + title.toLowerCase() + "]");
System.out.println("[" + title.trim() + "]");
System.out.println("[" + title + "]");

[  TEA TIME ]
[  tea time ]
[Tea Time]
[  Tea Time ]

The last line shows that title is still what it was. No String method ever changes the string it's called on: Strings are immutable. To keep a result, store it, often in the same variable: title = title.trim();. A line like title.trim(); on its own does nothing useful, because the new string is thrown away, just like the value of a method call that isn't used (module 11).

Since each of these methods returns a string, you can call another method on the result straight away. title.trim().toUpperCase() trims first and then makes capitals of the trimmed text: TEA TIME.