java – 使用compareTo实现equals方法

一般问题：在 Java中实现一个默认equals方法的覆盖时,应该如何使用已经实现的compareTo方法来将独立逻辑写入equals方法呢？我注意到有人在另一个问题中提到foo.equals((String)null)返回false,而String.compareTo((String)null)抛出一个NullPointerException.使这些不一致的结果成为理想的功能？

样本等于方法：

@Override
public boolean equals(Object obj) {
    if (obj != null && obj instanceof MyClass) {
        MyClass msg = (MyClass)obj;
        return this.compareTo(msg) == 0;
    }
    return false;
}

编辑：
从Comparable的文档引用

The natural ordering for a class C is said to be consistent with
equals if and only if e1.compareTo(e2) == 0 has the same boolean value
as e1.equals(e2) for every e1 and e2 of class C. Note that null is not
an instance of any class,and e.compareTo(null) should throw a
NullPointerException even though e.equals(null) returns false

编辑：

经过进一步审查,我发现注意到,Comparable文件还说明如下：

The implementor must ensure sgn(x.compareTo(y)) == -sgn(y.compareTo(x)) for all x and y. (This implies that x.compareTo(y) must throw an exception iff y.compareTo(x) throws an exception.)

Ergo,因为null.compareTo(x)显然会抛出一个NPE,x.compareTo(null)也应该抛出一个NPE.而对于平等而言,情况并非如此.对于NPE的正确处理我很大,所以我觉得这个比较重要.