在Java代码中如何重写equals和hashCode呢?

下文笔者讲述java代码重写equals和hashCode的示例分享,如下所示

equals和hashCode方法用途

当我们比较两个java对象时,
    此时笔者建议大家重写equals和hashCode方法

例:重写equals和hashCode方法的示例

 
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;
    }
 
}

JDK 7及更高版本的重写方法

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);
    }
}

Apache Commons Lang中EqualsBuilder和HashCodeBuilder函数

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();
    } 
}