紧凑等于和哈希码

Question

我有一个有4个属性的bean:

user
institutionId
groupId
postingDate

我使用Eclipse生成equals和hashcode,但结果代码并不漂亮.是否有一种紧凑的方式来做同样的事情？假设我希望equals和hashcode使用所有属性或它们的子集.

@Override
public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result + ((groupId == null) ? 0 : groupId.hashCode());
    result = prime * result + ((institutionId == null) ? 0 : institutionId.hashCode());
    result = prime * result + ((postingDate == null) ? 0 : postingDate.hashCode());
    result = prime * result + ((user == null) ? 0 : user.hashCode());
    return result;
}

@Override
public boolean equals(Object obj) {
    if (this == obj)
        return true;
    if (obj == null)
        return false;
    if (getClass() != obj.getClass())
        return false;
    ManGroupKey other = (ManGroupKey) obj;
    if (groupId == null) {
        if (other.groupId != null)
            return false;
    } else if (!groupId.equals(other.groupId))
        return false;
    if (institutionId == null) {
        if (other.institutionId != null)
            return false;
    } else if (!institutionId.equals(other.institutionId))
        return false;
    if (postingDate == null) {
        if (other.postingDate != null)
            return false;
    } else if (!postingDate.equals(other.postingDate))
        return false;
    if (user == null) {
        if (other.user != null)
            return false;
    } else if (!user.equals(other.user))
        return false;
    return true;
}

Answer 1

在Java 7中

public int hashCode() {
    return Objects.hash(groupId, institutionId, postingDate, user);
}

public boolean equals(Object obj) {
    if (this == obj)
        return true;
    if (obj == null)
        return false;
    if (getClass() != obj.getClass())
        return false;

    // cast to correct class
    Target o = (Target)obj;

    return Objects.equals(groupId, o.groupId) &&
           Objects.equals(institutionId, o.institutionId) &&
           Objects.equals(postingDate, o.postingDate) &&
           Objects.equals(user, o.user);
}

Answer 2

你可以压缩代码,但是你引入错误的几率远高于你做任何有用的东西.equals和hash code方法的所有部分都有一个原因.

如果它困扰你,大多数IDE都有折叠编辑器,只需点击黄色小框(通常),方法的所有内容都会被隐藏起来.

Answer 3

您可以使用 Apache-common-langs( http://commons.apache.org/proper/commons-lang/ ) 类 HashCodeBuilder 和 EqualsBuilder 来执行此操作，而不是使用 eclipse 生成的代码：

public int hashCode() {
   return HashCodeBuilder.reflectionHashCode(this);
}


public boolean equals(Object obj) {
   return EqualsBuilder.reflectionEquals(this);
 }