Arrays and Strings - Beginning Java - page 164

Test 2
string3 is now: Too many cooks
string1 is now: Too many cooks
string1 == string3 is true. string1 and string3 point to the same
string
How It Works
The three variables string1 , string2 , and string3 are initialized with the string literals you see. After
executing the assignment statement, the string referenced by string1 is identical to that referenced by
string3 , but as you see from the output, the comparison for equality in the if statement returns false
because the variables refer to two separate strings. Note that if you were to just initialize string1 and
string3 with the same string literal, "Too many cooks" , only one String object would be created,
which both variables would reference. This would result in both comparisons being true .
Next you change the value of string3 so that it refers to the same string as string1 . The output demon-
strates that the if expression has the value true , and that the string1 and string3 objects do indeed
refer to the same string. This clearly shows that the comparison is not between the strings themselves,
but between the references to the strings. So how do you compare the strings?
Comparing Strings for Equality
To compare two String variables, that is, to decide whether the strings they reference are equal or not, you
must use the equals() method, which is defined for objects of type String . For example, to compare the
String objects referenced by the variables string1 and string3 you could write the following statement:
if(string1.equals(string3)) {
System.out.println("string1.equals(string3) is true." +
" so strings are equal.");
}
This calls the equals() method for the String object referenced by string1 and passes string3 as
the argument. The equals() method does a case-sensitive comparison of corresponding characters in the
strings and returns true if the strings are equal and false otherwise. Two strings are equal if they are the
same length, that is, have the same number of characters, and each character in one string is identical to the
corresponding character in the other.
Of course, you could also use the equals() method for the string referenced by string3 to do the com-
parison:
if(string3.equals(string1)) {
System.out.println("string3.equals(string1) is true." +
" so strings are equal.");
}
This is just as effective as the previous version.
To check for equality between two strings ignoring the case of the string characters, you use the method
equalsIgnoreCase() . Let's put these methods in the context of an example to see them working.