Override equals() method only of a Java object

问题:

I am developing an Android application which makes use of the ScanResult object. This object is in the form of:

[SSID: __mynetwork__, BSSID: 00:0e:2e:ae:4e:85, capabilities: [WPA-PSK-TKIP][ESS], level: -69, frequency: 2457, timestamp: 117455824743]

How would I override only the equals() method without creating a customer class which extends it in order to compare only the SSID, BSSID, capabilties, level and frequency attributes only? In other words, in the equals method I want to eliminate the timestamp attribute, so that when I compare these two objects, the equals() method would return a true value:

[SSID: __mynetwork__, BSSID: 00:0e:2e:ae:4e:85, capabilities: [WPA-PSK-TKIP][ESS], level: -69, frequency: 2457, timestamp: 117455824743]
[SSID: __mynetwork__, BSSID: 00:0e:2e:ae:4e:85, capabilities: [WPA-PSK-TKIP][ESS], level: -69, frequency: 2457, timestamp: 117460312231]

Note: When I derive a customer class which extends ScanResult I get the following error when I try to implement a constructor: The constructor ScanResult() is not visible

回答1:

You just have to implement it without checking the fields you want to ignore. Don't forget to override the hashode() too.

@Override
public int hashCode() {
    final int prime = 31;
    int result = 1;
    result = prime * result
            + ((field1 == null) ? 0 : field1.hashCode());
    result = prime * result + ((field2 == null) ? 0 : field2.hashCode());
            ...etc
    return result;
}

@Override
public boolean equals(Object obj) {
    if (this == obj)
        return true;
    if (obj == null)
        return false;
    if (getClass() != obj.getClass())
        return false;
    ScanResult other = (ScanResult ) obj;
    if (field1 == null) {
        if (other.field1 != null)
            return false;
    } else if (!field1.equals(other.field1))
        return false;
    if (field2 == null) {
        if (other.field2 != null)
            return false;
    } else if (!field2 .equals(other.field2 ))
        return false;
        }
... etc
}

回答2:

This is your Overriden equals() Method....

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

    if(!BSSID.equals(o.BSSID)) return false;
    if(!SSID.equals(o.SSID)) return false;
    if(!capabilities.equals(o.capabilities)) return false;
    if(frequency != o.frequency) return false;
    if(level != o.level) return false;

    return true;
}

EDIT

Now that the above solution not working, may I suggest:

class ScanResultComparator {
    public static boolean equals(ScanResult a, ScanResult b){
        if(!a.BSSID.equals(b.BSSID)) return false;
        if(!a.SSID.equals(b.SSID)) return false;
        if(!a.capabilities.equals(b.capabilities)) return false;
        if(a.frequency != b.frequency) return false;
        if(a.level != b.level) return false;

        return true;
    }
}

回答3:

Extend the ScanResult class and only override the equals() method

class CustomScanResult extends ScanResult {

    @Override
    public boolean equals(Object o) {
        // ... custom logic ...
    }

}