问题引入

POJO 类需要编写equals, hashCode 和 toString方法，通常只需要一个模板就能完成，目前我们已经可以让IDE使用插件来帮我们完成这些工作。但是通常由IDE自动生成的这些代码都非常难看：

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public class UserAddrInfo implements Serializable {

    private static final long serialVersionUID = 1900570942803605101L;

    /**
     * 用户uid
     */
    private Integer uid;

    /**
     * 省
     */
    private String province;

    /**
     * 市
     */
    private String city;

    /**
     * 区
     */
    private String area;

    /**
     * 详细地址( 领地一 / 领地二 )
     */
    private String addrDetail;

// constructor
// getters, setters if needed
}

通常做法

目前的主流IDE都能够生成符合需求的方法的代码，但是生成的equals、hashCode和toString方法代码通常看起来就像下面这样：

equals

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@Override
public boolean equals(Object o) {
    if (this == o) return true;
    if (o == null || getClass() != o.getClass()) return false;

    UserAddrInfo that = (UserAddrInfo) o;

    if (uid != null ? !uid.equals(that.uid) : that.uid != null) return false;
    if (province != null ? !province.equals(that.province) : that.province != null) return false;
    if (city != null ? !city.equals(that.city) : that.city != null) return false;
    if (area != null ? !area.equals(that.area) : that.area != null) return false;
    return addrDetail != null ? addrDetail.equals(that.addrDetail) : that.addrDetail == null;

}

hashCode

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@Override
public int hashCode() {
    int result = uid != null ? uid.hashCode() : 0;
    result = 31 * result + (province != null ? province.hashCode() : 0);
    result = 31 * result + (city != null ? city.hashCode() : 0);
    result = 31 * result + (area != null ? area.hashCode() : 0);
    result = 31 * result + (addrDetail != null ? addrDetail.hashCode() : 0);
    return result;
}

toString

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@Override
    public String toString() {
        return "UserAddrInfo{" +
                "uid=" + uid +
                ", province='" + province + '\'' +
                ", city='" + city + '\'' +
                ", area='" + area + '\'' +
                ", addrDetail='" + addrDetail + '\'' +
                '}';
    }

使用Guava库来解决

Google Guava是一个提供了很多非常使用Java工具的精巧的库。我们可以使用Google Guava来重写上面的三个方法来使得代码显得更好看：

equals

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@Override
public boolean equals(Object o) {
    if (this == o) return true;
    if (o == null || getClass() != o.getClass()) return false;
    UserAddrInfo that = (UserAddrInfo) o;
    return Objects.equal(uid, that.uid) &&
            Objects.equal(province, that.province) &&
            Objects.equal(city, that.city) &&
            Objects.equal(area, that.area) &&
            Objects.equal(addrDetail, that.addrDetail);
}

hashCode – 只需要一行

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@Override
public int hashCode() {
    return Objects.hashCode(uid, province, city, area, addrDetail);
}

toString

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@Override
public String toString() {
    return Objects.toStringHelper(this)
            .add("uid", uid)
            .add("province", province)
            .add("city", city)
            .add("area", area)
            .add("addrDetail", addrDetail)
            .toString();
}