Java - Comment remplacer equals et hashCode
Quelques exemples Java pour vous montrer comment remplacerequals ethashCode.
1. POJO
Pour comparer deux objets Java, nous devons remplacer à la foisequals ethashCode (bonne pratique).
User.java
public class User {
private String name;
private int age;
private String passport;
//getters and setters, constructor
}
User user1 = new User("example", 35, "111222333");
User user2 = new User("example", 35, "111222333");
System.out.println(user1.equals(user2)); // false
2. Manière classique
L'idée du code de hachage 17 et 31 est tirée du livre Java classique - Java efficace: point 9
User.java
public class User {
private String name;
private int age;
private String passport;
//getters and setters, constructor
@Override
public boolean equals(Object o) {
if (o == this) return true;
if (!(o instanceof User)) {
return false;
}
User user = (User) o;
return user.name.equals(name) &&
user.age == age &&
user.passport.equals(passport);
}
//Idea from effective Java : Item 9
@Override
public int hashCode() {
int result = 17;
result = 31 * result + name.hashCode();
result = 31 * result + age;
result = 31 * result + passport.hashCode();
return result;
}
}
2. JDK 7
Pour JDK 7 et supérieur, vous pouvez utiliser la nouvelle classeObjects pour générer les valeurs de code égal et de hachage.
User.java
import java.util.Objects;
public class User {
private String name;
private int age;
private String passport;
//getters and setters, constructor
@Override
public boolean equals(Object o) {
if (o == this) return true;
if (!(o instanceof User)) {
return false;
}
User user = (User) o;
return age == user.age &&
Objects.equals(name, user.name) &&
Objects.equals(passport, user.passport);
}
@Override
public int hashCode() {
return Objects.hash(name, age, passport);
}
}
3. Apache Commons Lang
Vous pouvez également utiliser les fonctions Apache Commons LangEqualsBuilder etHashCodeBuilder.
User.java
import org.apache.commons.lang3.builder;
public class User {
private String name;
private int age;
private String passport;
//getters and setters, constructor
@Override
public boolean equals(Object o) {
if (o == this) return true;
if (!(o instanceof User)) {
return false;
}
User user = (User) o;
return new EqualsBuilder()
.append(age, user.age)
.append(name, user.name)
.append(passport, user.passport)
.isEquals();
}
@Override
public int hashCode() {
return new HashCodeBuilder(17, 37)
.append(name)
.append(age)
.append(passport)
.toHashCode();
}
}
4. Testez à nouveau
After remplace à la foisequals ethashCode.
User user1 = new User("example", 35, "111222333");
User user2 = new User("example", 35, "111222333");
System.out.println(user1.equals(user2)); // true