Java Reference
In-Depth Information
The interface terminology is also used for individual methods. For example, the String docu-
mentation shows us the interface of the length method:
public int length()
Returns the length of this string. The length is equal to the number of Unicode code
units in the string.
Specified by:
length in interface CharSequence
the length of the sequence of characters represented by this object.
The interface of a method consists of the signature of the method and a comment (shown here
in italics). The signature of a method includes (in this order):
an access modifier (here public ), which we shall discuss below;
the return type of the method (here int );
the method name;
a list of parameters (which is empty in this example).
The interface provides everything we need to know to make use of this method.
Using library-class methods
Back to our TechSupport system. We now want to improve the processing of input a little. We
have seen in the discussion above that our system is not very tolerant: if we type “Bye” or
“ bye” instead of “bye”, for instance, the word is not recognized. We want to change that by
adjusting the text read in from a user so that these variations are all recognized as “bye”.
The documentation of the String class tells us that it has a method called trim to remove
spaces at the beginning and the end of the string. We can use that method to handle the second
problem case.
Exercise 5.7 Find the trim method in the String class's documentation. Write down the
signature of that method. Write down an example call to that method on a String variable
called text .
objects. An object
is said to be immu-
table if its contents
or state cannot be
changed once it
has been created.
Strings are an ex-
ample of immutable
One important detail about String objects is that they are immutable —that is, they cannot be
modified once they have been created. Note carefully that the trim method, for example, re-
turns a new string; it does not modify the original string. Pay close attention to the following
“Pitfall” comment.
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