import java.util.HashSet;
import java.util.Set;
/**
* Override_Annotation_Usage_Example, from Effective Java
*/
public class MyCharacterSet {
private final char first;
private final char second;
public MyCharacterSet(char first, char second) {
this.first = first;
this.second = second;
}
public boolean equals(MyCharacterSet b) {
return b.first == first && b.second == second;
}
public int hashCode() {
return 31 * first + second;
}
public static void main(String[] args) {
Set s = new HashSet();
for (int i = 0; i < 10; i++)
for (char ch = 'a'; ch <= 'z'; ch++)
s.add(new MyCharacterSet(ch, ch));
System.out.println(s.size());
}
}
Can you notice the error in above code ?The equals method does not override: The original Object::equals is boolean equals(Object), while the overridden equals is boolean equals(MyCharacterSet ), which has a different method signature, which does not override. Adding @Override to the equals will detect this blunder.
Correction : change the method signature as :
@Override
public boolean equals(Object arg0) {
MyCharacterSet b = (MyCharacterSet) arg0;
return b.first == first && b.second == second;
}
You should use the @Override annotation if the lack of a method with the same signature in a superclass is indicative of a bug.
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