Java Idiom

equals() And hashCode() Contracts

• If two objects are equal according to the equals() method, then their hash codes must be equal as well.
• If two objects have the same hash code, they may or may not be equal according to the equals() method.

equals

@Override
public boolean equals(Object o) {
	if (this == o) return true;
	if (!(o instanceof Dog)) return false;
	Dog dog = (Dog) o;
	return getAge() == dog.getAge() && getName().equals(dog.getName()) && getBreed().equals(dog.getBreed());
    }

hashCode

@Override
public int hashCode() {
	final int prime = 31;
	int result = 1;
	result = (prime * result) + columnIndex;
	result = (prime * result) + rowIndex;
	return result;
}

Links

• Java Practices→Defensive copying
• Java Practices→Copy constructors
• Java Practices→Factory methods