Reference types - Data Structures and Problem Solving Using Java - page 36

Single-character strings should not be replaced with character constants;
Exercise 2.7 asks you to show why. Note that operator + is left-associative,
and thus

"a" + 1 + 2 // Generates "a12"
1 + 2 + "a" // Generates "3a"
1 + ( 2 + "a" ) // Generates "12a"

Also, operator += is provided for the String . The effect of str+=exp is the
same as str=str+exp . Specifically, this means that str will reference the newly
constructed String generated by str+exp .

2.3.3 comparing strings

Since the basic assignment operator works for String s, it is tempting to
assume that the relational and equality operators also work. This is not
true.
In accordance with the ban on operator overloading, relational operators
( < , > , <= , and >= ) are not defined for the String type. Further, == and != have the
typical meaning for reference variables. For two String objects lhs and rhs ,
for example, lhs==rhs is true only if lhs and rhs refer to the same String
object. Thus, if they refer to different objects that have identical contents,
lhs==rhs is false . Similar logic applies for != .
To compare two String objects for equality, we use the equals method.
lhs.equals(rhs) is true if lhs and rhs reference String s that store identical
values.
A more general test can be performed with the compareTo method.
lhs.compareTo(rhs) compares two String objects, lhs and rhs . It returns a neg-
ative number, zero, or a positive number, depending on whether lhs is lexico-
graphically less than, equal to, or greater than rhs , respectively.

Use equals and
compareTo to per-
form string
comparison.

2.3.4 other String methods

The length of a String object (an empty string has length zero) can be
obtained with the method length . Since length is a method, parentheses are
required.
Two methods are defined to access individual characters in a String . The
method charAt gets a single character by specifying a position (the first posi-
tion is position 0). The method substring returns a reference to a newly con-
structed String . The call is made by specifying the starting point and the first
nonincluded position.
Here is an example of these three methods:

Use length , charAt ,
and substring to
compute string
length, get a single
character, and get
a substring,
respectively.