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As a general rule, use the Object.equals() method to check whether two objects are abstractly equal to each other . Programs must reserve use of and the equality operators == and != for testing to test whether two references specifically refer to the same object; this is reference . This latter test is referred to as referential equality. Also see MET09-J. Classes that define an equals() method must also define a hashCode() method .
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The reference equality operator == evaluates to true only when the values it compares reference the same underlying object. This noncompliant example declares two distinct String objects that contain the same value to be true. The references, however, are unequal because they reference distinct objects.
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public class StringComparison {
public static void main(String[] args) {
String str1 = new String("one");
String str2 = new String("one");
System.out.println(isEqual( str1, str2)); // prints "false"
}
public static boolean isEqual(String str1, String str2) {
boolean result;
// test for null is redundant in this case, but required for full generality
if (str1 == null) {
result = str2 == null;
}
else {
result = str1 == str2;
}
return result; // false!
}
}
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Compliant Solution (Object.equals())
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public class StringComparison {
public static booleanvoid isEqual(main(String[] args) {
String str1, = new String str2) {
boolean result;
// test for null is redundant in this case, but required for full generality("one");
String str2 = new String("one");
System.out.println(isEqual(str1, str2)); // prints "true"
}
public static boolean isEqual(String str1, String str2) {
boolean result;
if (str1 == null) {
result = (str2 == null);
} else {
result = str1.equals(str2);
}
return result; // true
}
}
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Compliant Solution (String.intern())
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ES: Comparison of String objects using == or != | |
[JLS 2005] | |
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02. Expressions (EXP) EXP02-J. Use the two-argument Arrays.equals() method to compare the contents of arrays