常用方法之equals

equals是超父类Object的方法,即所有的java对象都拥有此方法.
下面是Object的源码

public boolean equals(Object obj) {
        return (this == obj);
    }

可以看出,Bean如果不重写equals方法,直接调用则是==比较
==比较,基本类型通常是比较的值,引用类型比较的是引用即引用地址值.
String类型和基本类型的包装类,equals方法还是比较的值,因为这些类重写了equals方法.

public boolean equals(Object anObject) {
        if (this == anObject) {
            return true;
        }
        if (anObject instanceof String) {
            String anotherString = (String)anObject;
            int n = value.length;
            if (n == anotherString.value.length) {
                char v1[] = value;
                char v2[] = anotherString.value;
                int i = 0;
                while (n-- != 0) {
                    if (v1[i] != v2[i])
                        return false;
                    i++;
                }
                return true;
            }
        }
        return false;
    }

上面是String重写的equals,可以看出字符串比较时会先比较引用地址,如果地址不同,然后会比较字符串长度,然后比较每一个字符,如果相同则结果依然true.

public boolean equals(Object obj) {
        if (obj instanceof Integer) {
            return value == ((Integer)obj).intValue();
        }
        return false;
    }
public boolean equals(Object obj) {
        if (obj instanceof Long) {
            return value == ((Long)obj).longValue();
        }
        return false;
    }

基本类型的包装类,会直接转为基本类型使用==比较,即基本类型比较值.
所以当我们需要判断使用的POJO唯一时,就必须要重写equals方法,IDE重写的equals方法模板,会对每一个属性进行比较,如果属性有引用类型,也必须保证该引用类型重写了equals,比如下面的pojo

@Setter
@Getter
@ToString
public class PersonRequest {
    /**
     * 联系人基本信息
     */
    @Valid()
    private PersonBasicInfoAO personBasicInfo;
    /**
     * 联系人任职信息
     */
    @Valid
    private List<PersonDutyAO> personDuties;
    /**
     * 人员联系方式入参
     */
    @Valid
    private List<PersonContactAO> personContacts;
    /**
     * 教育信息
     */
    @Valid
    private List<PersonEducationAO> personEducations;
    /**
     * 工作经历
     */
    @Valid
    private List<PersonResumeAO> personResumes;
    /**
     * 请求来源（PC端/移动端）
     */
    private String requestSource;

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof PersonRequest)) return false;

        PersonRequest that = (PersonRequest) o;

        if (personBasicInfo != null ? !personBasicInfo.equals(that.personBasicInfo) : that.personBasicInfo != null)
            return false;
        if (personDuties != null ? !personDuties.equals(that.personDuties) : that.personDuties != null) return false;
        if (personContacts != null ? !personContacts.equals(that.personContacts) : that.personContacts != null)
            return false;
        if (personEducations != null ? !personEducations.equals(that.personEducations) : that.personEducations != null)
            return false;
        if (personResumes != null ? !personResumes.equals(that.personResumes) : that.personResumes != null)
            return false;
        return requestSource != null ? requestSource.equals(that.requestSource) : that.requestSource == null;
    }    
}