java - 使用相等和可比较接口(interface)的对象比较

Question

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Answer 1

来自 Comparable

It is strongly recommended, but not strictly required that (x.compareTo(y)==0) == (x.equals(y)). Generally speaking, any class that implements the Comparable interface and violates this condition should clearly indicate this fact. The recommended language is "Note: this class has a natural ordering that is inconsistent with equals."

正如@ZouZou 提到的

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.

这意味着它们不可互换。

在 java api 中发生这种情况的示例在 BigDecimal 中

import java.math.BigDecimal;

public class Test{
 public static void main(String args[])  {

       BigDecimal big = BigDecimal.ZERO;
       BigDecimal zero  = new BigDecimal("0.00");

       System.out.println("Compare "+ (big.compareTo(zero) == 0) ); //prints true
       System.out.println("Equals "+big.equals(zero)); // prints false      
 } 
}