...
| Code Block |
|---|
|
public final class CreditCard {
private final int number;
public CreditCard(int number) {
this.number = (short) number;
}
public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof CreditCard))
return false;
CreditCard cc = (CreditCard)o;
return cc.number == number;
}
public static void main(String[] args) {
Map m = new HashMap();
m.put(new CreditCard(100), "Java");
System.out.println(m.get(new CreditCard(100)));
}
}
|
Compliant Solution
| Wiki Markup |
|---|
This compliant solution shows how {{hashCode}} can be overridden so that the same value is generated for an instance. The recipe to generate such a hash function is described |
in Effective Java Language Programming, Item 8 in \[[Bloch 08|AA. Java References#Bloch 08]\] Item 9: Always override {{hashCode}} when you override {{equals}}. |
| Code Block |
|---|
|
public final class CreditCard {
private final int number;
public CreditCard(int number) {
this.number = (short) number;
}
public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof CreditCard))
return false;
CreditCard cc = (CreditCard)o;
return cc.number == number;
}
public int hashCode() {
int result = 7;
result = 37*result + number;
return result;
}
public static void main(String[] args) {
Map m = new HashMap();
m.put(new CreditCard(100), "Java");
System.out.println(m.get(new CreditCard(100)));
}
}
|
...
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
References
| Wiki Markup |
|---|
\[[Bloch 08|AA. Java References#Bloch 08]\] Item 9: Always override {{hashCode}} when you override {{equals}}
\[[API 06|AA. Java References#API 06]\] [Class Object|http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Object.html] |
Effective Programming in Java. Item 8 java.lang.Object Documentation
