Arrays and Strings - Beginning Java 2 SDK - page 137

// Display the contents of the strings
System.out.println("\n\nTest 2");
System.out.println("string3 is now: " + string3);
System.out.println("string1 is now: " + string1);
if(string1 == string3) // Now test for identity
System.out.println("string1 == string3 is true." +
" string1 and string3 point to the same string");
else
System.out.println("string1 == string3 is false." +
" string1 and string3 do not point to the same string");
}
}
We have created two scenarios. In the first, the variables string1 and string3 refer to separate strings
that happen to be identical. In the second, they both reference the same string. This will produce the output:
Test 1
string3 is now: Too many cooks
string1 is now: Too many cooks
string1==string3 is false. string1 and string3 do not point to the same string
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 will be 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.
Next we change the value of string3 so that it refers to the same string as string1 . The output
demonstrates 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 we 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 method equals() , which is defined in the String class. This method does a case
sensitive comparison. 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.
To check for equality between two strings ignoring the case of the string characters, you use the method
equalsIgnoreCase() . Let's put these in the context of an example to see how they work.