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| 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""Java");
// Assuming Integer.MAX_VALUE is the largest number for card
System.out.println(m.get(new CreditCard(100)));
}
}
|
...
| Code Block | ||
|---|---|---|
| ||
import java.util.Map;
import java.util.HashMap;
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""Java");
System.out.println(m.get(new CreditCard(100)));
}
}
|
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| Wiki Markup |
|---|
\[[API 06|AA. Java References#API 06]\] [Class Object|http://java.sun.com/javase/6/docs/api/java/lang/Object.html]
\[[Bloch 08|AA. Java References#Bloch 08]\] Item 9: Always override {{hashCode}} when you override {{equals}}
\[[MITRE 09|AA. Java References#MITRE 09]\] [CWE ID 581|http://cwe.mitre.org/data/definitions/581.html] ""Object Model Violation: Just One of Equals and Hashcode Defined"" |
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MET30-J. Follow the general contract while overriding the equals method 12. Methods (MET) MET32-J. Ensure that constructors do not call overridable methods