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By operating on String objects, the CaseInsensitiveString.equals() method violates the second contract requirement (symmetry). Because of the asymmetry, given a String object s and a CaseInsensitiveString object cis that differ only in case, cis.equals(s)) returns true, while s.equals(cis) returns false.
Note that this code also violates rule MET09-J. Classes that define an equals() method must also define a hashCode() method.
Compliant Solution
In this compliant solution, the CaseInsensitiveString.equals() method is simplified to operate only on instances of the CaseInsensitiveString class, consequently preserving symmetry. The class also complies with rule {MET09-J. Classes that define an equals() method must also define a hashCode() method] by defining a hashCode() method.
| Code Block | ||
|---|---|---|
| ||
public final class CaseInsensitiveString {
private String s;
public CaseInsensitiveString(String s) {
if (s == null) {
throw new NullPointerException();
}
this.s = s;
}
public boolean equals(Object o) {
return o instanceof CaseInsensitiveString &&
((CaseInsensitiveString)o).s.equalsIgnoreCase(s);
}
public int hashCode() {
// ...
}
public static void main(String[] args) {
CaseInsensitiveString cis = new CaseInsensitiveString("Java");
String s = "java";
System.out.println(cis.equals(s)); // Returns false now
System.out.println(s.equals(cis)); // Returns false now
}
}
|
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The method java.lang.Object.equals() by default is unable to compare composite objects such as cryptographic keys. Most Key classes lack an equals() implementation that overrides would override Object's default implementation. In such cases, the components of the composite object must be compared individually to ensure correctness.
...
| Code Block | ||
|---|---|---|
| ||
private static boolean keysEqual(Key key1, Key key2) {
if (key1.equals(key2)) {
return true;
}
}
|
Compliant Solution (java.security.Key)
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<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="965aada99a65afbb-8bddcc34-47d046a1-8d2386b2-cf111db495889b766f34c164"><ac:plain-text-body><![CDATA[ | [[API 2006 | AA. Bibliography#API 06]] | [Method | http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Object.html#equals(java.lang.Object)] | ]]></ac:plain-text-body></ac:structured-macro> |
<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="ee433128b9c844fe-12c459e7-44414c47-91019cac-4a006a1f186e19a3fd3a76b1"><ac:plain-text-body><![CDATA[ | [[Bloch 2008 | AA. Bibliography#Bloch 08]] | Item 8. Obey the general contract when overriding equals | ]]></ac:plain-text-body></ac:structured-macro> | |
<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="1fdb6f92a20da4c8-7434ae1f-4e9e498a-aebaabf5-f4bbf201a0b934d7437364e1"><ac:plain-text-body><![CDATA[ | [[Darwin 2004 | AA. Bibliography#Darwin 04]] | 9.2, Overriding the | ]]></ac:plain-text-body></ac:structured-macro> | |
<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="91f0c0355540a5ab-0d3a42eb-4a5543c8-ad5c95ad-fad2af2b91b3a3b0000e3afa"><ac:plain-text-body><![CDATA[ | [[Harold 1997 | AA. Bibliography#Harold 97]] | Chapter 3, Classes, Strings, and Arrays, The Object Class (Equality) | ]]></ac:plain-text-body></ac:structured-macro> | |
<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="1bb1781f11af78d0-fb36b425-45c6452e-b988a104-8d78454928b5f4ac0a1f5f23"><ac:plain-text-body><![CDATA[ | [[Sun 2006 | AA. Bibliography#Sun 06]] | [Determining If Two Keys Are Equal | http://java.sun.com/javase/6/docs/technotes/guides/security/crypto/CryptoSpec.html#Determining%20If%20Two%20Keys%20Are%20Equal] (JCA Reference Guide) | ]]></ac:plain-text-body></ac:structured-macro> |
<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="791b5e86699ac2e5-c799b4f2-462f494f-9b4dbfa1-a2bfb1940e468a94b4b0ef76"><ac:plain-text-body><![CDATA[ | [[Techtalk 2007 | AA. Bibliography#Techtalk 07]] | More Joy of Sets | ]]></ac:plain-text-body></ac:structured-macro> |
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