#2 Optimise hashCode() and toString()

[Ludovic Claude]

Provide an optimised version of hashCode() and
toString() when the object is immuable (all fields are
declared final).

For example:

public class Person {
private final String firstName;
private final String lastName;
// added by commonClipse
private transient int hashCode = 0;
private transient String toString = null;

public Person(String firstName, String lastName) {
this.firstName = firstName;
this.lastName = lastName;
}

public String getFirstName() {
    return firstName;
}

public String getLastName() {
    return firstName;
}

 public int hashCode() {
    if (hashCode == 0) {
        hashCode = HashCodeBuilder(357504959,

1759723435)
.append(this.firstName)
.append(this.lastName)
.toHashCode();
}
return hashCode;
}

 public String toString() {
     if (toString == null) {
    toString = new ToStringBuilder(this)
        .append("firstName", this.firstName)
        .append("lastName", this.lastName)
        .toString();
}
    return toString;
}

}

[David Dossot]

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I suggest you compute the hashcode and toString value at construction time instead of lazily as shown in the code.

Rationale: immutable object are intrinsically threadsafe, but by having some attributes calculated in a thread-unsafe manner (you can easily have several threads calculating the hashcode or the toString at the same time), you somewhat break this expectation.