Question

我创建了一个Address类，如下所示，然后我想检查两个Address es的相等性。如果所有字段都相同，则两个Address es被认为是相同的。< / p>

因此，我实施了hashCode和equals方法。

public class Address{

    public String addressLine1;

    public String addressLine2;

    public String city;     

    public String state;

    public String pincode;

    public String phoneNumber;      

    public String country; 

    public Address() {

    }

    public Address(String addressLine1, String addressLine2, String city,
            String state, String pincode, String phoneNumber, String country) {         
        this.addressLine1 = addressLine1;
        this.addressLine2 = addressLine2;
        this.city = city;
        this.state = state;
        this.pincode = pincode;
        this.phoneNumber = phoneNumber;
        this.country = country;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = super.hashCode();
        result = prime * result
                + ((addressLine1 == null) ? 0 : addressLine1.hashCode());
        result = prime * result
                + ((addressLine2 == null) ? 0 : addressLine2.hashCode());
        result = prime * result + ((city == null) ? 0 : city.hashCode());
        result = prime * result + ((country == null) ? 0 : country.hashCode());
        result = prime * result
                + ((phoneNumber == null) ? 0 : phoneNumber.hashCode());
        result = prime * result + ((pincode == null) ? 0 : pincode.hashCode());
        result = prime * result + ((state == null) ? 0 : state.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        System.out.println("equals("+obj);
        if (this == obj)
            return true;
        if (!super.equals(obj))
            return false;
        if (getClass() != obj.getClass())
            return false;
        Address other = (Address) obj;
        if (addressLine1 == null) {
            if (other.addressLine1 != null)
                return false;
        } else if (!addressLine1.equals(other.addressLine1))
            return false;
        if (addressLine2 == null) {
            if (other.addressLine2 != null)
                return false;
        } else if (!addressLine2.equals(other.addressLine2))
            return false;
        if (city == null) {
            if (other.city != null)
                return false;
        } else if (!city.equals(other.city))
            return false;
        if (country == null) {
            if (other.country != null)
                return false;
        } else if (!country.equals(other.country))
            return false;
        if (phoneNumber == null) {
            if (other.phoneNumber != null)
                return false;
        } else if (!phoneNumber.equals(other.phoneNumber))
            return false;
        if (pincode == null) {
            if (other.pincode != null)
                return false;
        } else if (!pincode.equals(other.pincode))
            return false;
        if (state == null) {
            if (other.state != null)
                return false;
        } else if (!state.equals(other.state))
            return false;
        return true;
    }

    public String toString() {
        return this.addressLine1+","+this.addressLine2+","+this.city+","+this.state+","+this.pincode+","+this.country+","+this.phoneNumber;
    }

}

在这个类的TestCase中，我尝试创建两个相同的地址并调用assertEquals ..但是这失败了..

类AddressTests扩展了UnitTest {

@Test
public void testAddressEquality() {
    Address address1 = new Address();
    address1.addressLine1 = "#1000,South Avenue";
    address1.state = "New York";
    address1.country = "U.S";
    System.out.println("address1="+address1);

    Address address2 = new Address();
    address2.addressLine1 = "#1000,South Avenue";
    address2.state = "New York";
    address2.country = "U.S";
    System.out.println("address2="+address2);

    assertEquals(address1,address2);

}

}

assertEquals失败

Failure, expected: models.Address<#1000,South Avenue,null,null,New York,null,U.S,null> but was: models.Address<#1000,South Avenue,null,null,New York,null,U.S,null>

有人可以帮我理解为什么会失败吗？

Answer 1

这是一个问题：

if (!super.equals(obj))
        return false;

Object.equals检查引用是否相同（与this == obj测试相同的测试）。你根本不想检查那里 - 你已经测试了参考相等性，如果对象引用不相同，你不想挽救。

表格the docs：

类Object的equals方法实现了对象上最具辨别力的等价关系;也就是说，对于任何非空引用值x和y，当且仅当x和y引用同一对象时，此方法才返回true（x == y的值为true）。

一个实现（OpenJDK）：

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

Answer 2

我认为你也应该修改你的哈希函数。为什么不只取其他哈希值的总和？你拥有它的方式，如果大多数字段不为null，结果超过20亿（Integer.MAX_VALUE），因此你绕过整数值。

Answer 3

你应该永远不要手动创建hashCode / equals ...让你选择的IDE为你做。

在IntelliJ IDEA中，简单的ALT + Insert，生成hashCode / equals。 Eclipse会以某种方式相似。

即使所有字段都相同，地址相等也会失败

3 个答案: