Java 天地·Core Java·Lecture Notes·Unit 5 - Arrays & Strings

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Review Question 5

If two Strings contain the same text, then we would expect them to be equal in some sense. For example, consider this section of Java:

String string1 = "hello";
String string2 = "hello";
String string3 = "there";
if (string1 == string2)
System.out.println("strings 1 and 2 are equal");
if (string1 == string3)
System.out.println("strings 1 and 3 are equal");

We might expect this section of program to print:

Strings 1 and 2 are equal

Because both contain the word "hello". In fact, neither line is printed; Java does not think the "hello" is equal to "hello"! This may seem rather odd at first. If x and y were integers, and both had the value 2 , thJava would think x and y were equal. So why does Java treat Strings and integers differently in this respect?

(Hint: what is different in the way these data types are implemented).

There is a short answer to this question, and a longer one which takes into account the philosophy behind the answer (i.e. why Java works this way).

If we can't use == to test whether two strings have the same text, how can we do it?

Discussion of Review Question 5

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