Java Syntax - Java for COBOL Programmers - page 158

if (s1 == s2) {
// This code will not execute
// even though the text contained in these
// two Strings are equal. s1 and s2 will
// point to different String objects
}
Yet the following test always succeeds since the equals() method in the String
class compares the value of the String object with the passed String:
if (s1.equals (s2)) {
... // This code will execute
}
What is the bottom line? Always use the equals() or compareTo() methods
when you want to compare two String s. Never assume that the String reference
variables will compare appropriately, based on the text values in the String .
Get ready for the real weirdness. Object reference variables are variables and,
therefore, can be assigned values. Normally, this happened only with the new key-
word, as in the following:
String s1 = new String ("Some text");
String s2 = new String ("Some other text");
But it is perfectly legal to set object reference s2 equal to s1 :
s2 = s1;
Now, both s2 and s1 point to the same object. (As a matter of fact, the object
formerly pointed to by s2 could be unreferenced and will likely be garbage collected
or deleted by the system at some point.) This time, the equality test, when applied
to the values of the String s, will succeed even though the initial object pointed to
by s2 was different from s1 :
if (s1.equals (s2)) {
... // This code would execute
}
The same is true of this test, which compares the object references:
if (s1 == s2) {