java - ArrayList contains() 未使用类的 equals() 方法

Question

我知道这个问题有很多答案。但我还没有找到解决方案。

class IpAddressRange
{
    InetAddress start;
    InetAddress end;

    public IpAddressRange(String start, String end) throws Exception
    {
        this.start = InetAddress.getByName(start);
        this.end = InetAddress.getByName(end);
    }

    @Override
    public boolean equals(Object input)
    {
        System.out.println("Inside equals");
        long lv = IpAddressRange.ipToLong(start);
        long hv = IpAddressRange.ipToLong(end);
        if(input != null && input instanceof InetAddress)
        {
            long iv = IpAddressRange.ipToLong((InetAddress)input);
            if( iv >= lv && iv <= hv)
                return true;
            }
            return false;
        }

    @Override
    public String toString()
    {
        return start.getHostAddress() + "-" + end.getHostAddress();
    }

    public static long ipToLong(InetAddress ip) {
        byte[] octets = ip.getAddress();
        long result = 0;
        for (byte octet : octets) {
            result <<= 8;
            result |= octet & 0xff;
        }
        return result;
    }
}

当我在 ArrayList 上使用 contains() 时，它没有使用 equals() 方法。

 ArrayList<IpAddressRange> allocatedList = new ArrayList<IpAddressRange>();
 allocatedList.add(new IpAddressRange("10.10.10.10","10.10.10.12"));

下面是调用contains()的代码:

 InetAddress inetAddress1 = InetAddress.getByName("10.10.10.11");
 allocatedList.contains(inetAddress1);

但是这个contains()并没有调用IpAdressRange类的equals()方法。

Answer 1

问题在于您的 equals() 实现与 InetAddress 的实现不一致。 equals() 方法应该是对称的。

看一下合约here :

The equals method implements an equivalence relation on non-null object references:

• It is reflexive: for any non-null reference value x, x.equals(x) should return true.
• It is symmetric: for any non-null reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true.
• It is transitive: for any non-null reference values x, y, and z, if x.equals(y) returns true and y.equals(z) returns true, then x.equals(z) should return true.
• It is consistent: for any non-null reference values x and y, multiple invocations of x.equals(y) consistently return true or consistently return false, provided no information used in equals comparisons on the objects is modified. For any non-null reference value x, x.equals(null) should return false.

重点是，您可以像 anIpAddressRange.equals(anInetAddress) 返回 true 一样实现它，但反之则不行，因为您无法编辑来自 InetAddress 的 equals() 方法。