class, which is not allways correct as you trivially found.
equals(Object) is intentionally informal about the meaning of equality.
Oliver Wong wrote:
...
*: Actually, making equals "aware" of class hierarchies is slightly trickier
than that. I wanted to gloss over this in my above example, but here's a
more complete example implementation:
public class SomeClass {
final int field1;
final String field2;
/*Constructors, getters, and hashcode*/
@Override
public boolean equals(Object other) {
if (other instanceof SomeClass) {
return equals((SomeClass)other);
}
return false;
}
public boolean equals(SomeClass other) {
if (!other.getClass().equals(this.getClass())) {
return other.equals(this);
}
if (this.field1 != other.field1) {
return false;
}
if (!this.field2.equals(other.field2)) {
return false;
}
return true;
}
}
I got worried about whether this code would ever make up its mind, given
a subclass comparison. It doesn't:
public class SomeClass {
final int field1 = 0;
final String field2 = "test";
public static void main(String[] args) {
Object obj1 = new SomeClass();
Object obj2 = new SomeSubClass();
System.out.println(obj1.equals(obj2));
}
/*Constructors, getters, and hashcode*/
@Override
public boolean equals(Object other) {
if (other instanceof SomeClass) {
return equals((SomeClass)other);
}
return false;
}
public boolean equals(SomeClass other) {
if (!other.getClass().equals(this.getClass())) {
return other.equals(this);
}
if (this.field1 != other.field1) {
return false;
}
if (!this.field2.equals(other.field2)) {
return false;
}
return true;
}
private static class SomeSubClass extends SomeClass{
}
}
This program results in a StackOverflowError. obj1 passes the comparison
to obj2, which passes it back to obj1... What am I doing wrong? Are
subclasses of SomeClass required to override equals with specific rules?
Patricia