未分类

数据的相等性比较引发的 BUG

问题

相同的代码逻辑，在不同的环境得出了不同的结果。在业务系统里是正确的，但是数据系统里却计算出了不同的结果。给一个示例：

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Integer x = 1234567;
Long y = 1234567L;
if (x.equals(y))) {
    // 处理业务逻辑
}

我们预期if语句判断能够成功并进入进行处理业务逻辑，但实际上这里会始终返回 false。这是因为java.lang.Integer和java.lang.Long的equals方法实现均会先判断类型，类型相同才会进行实际的相等性比较。Integer#equals方法实现如下：

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public boolean equals(Object obj) {
    if (obj instanceof Integer) {
        return value == ((Integer)obj).intValue();
    }
    return false;
}

怎样避免此类问题？

配置 IDEA 提升对于不兼容类型进行相等性比较时的检查级别

两个不兼容类型的相等性比较

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<component name="InspectionProjectProfileManager">
  <profile version="1.0">
    <option name="myName" value="Project Default" />
    <inspection_tool class="EqualsBetweenInconvertibleTypes" enabled="true" level="ERROR" enabled_by_default="true" editorAttributes="ERRORS_ATTRIBUTES" />
  </profile>
</component>

Java 17

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|  Welcome to JShell -- Version 17.0.6
|  For an introduction type: /help intro

jshell> var i = new Integer(12345678)
|  Warning:
|  Integer(int) in java.lang.Integer has been deprecated and marked for removal
|  var i = new Integer(12345678);
|          ^-------------------^
i ==> 12345678

jshell> Integer i = 12345678;
i ==> 12345678

jshell> Long l = 12345678L;
l ==> 12345678

jshell> i.equals(i, l)
|  Error:
|  method equals in class java.lang.Integer cannot be applied to given types;
|    required: java.lang.Object
|    found:    java.lang.Integer,java.lang.Long
|    reason: actual and formal argument lists differ in length
|  i.equals(i, l)
|  ^------^

jshell> Objects.equals(i, l)
$4 ==> false

jshell> i == l
|  Error:
|  incomparable types: java.lang.Integer and java.lang.Long
|  i == l
|  ^----^

其它语言

Scala

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(base) ➜  spring3-template git:(main) ✗ scala
Welcome to Scala 3.2.1 (17.0.6, Java OpenJDK 64-Bit Server VM).
Type in expressions for evaluation. Or try :help.

scala> val i = new java.lang.Integer(12345678)
there was 1 deprecation warning; re-run with -deprecation for details
1 warning found
val i: Integer = 12345678

scala> val l = new java.lang.Long(12345678)
there was 1 deprecation warning; re-run with -deprecation for details
1 warning found
val l: Long = 12345678

scala> i.equals(l)
val res0: Boolean = false

scala> java.util.Objects.equals(i, l)
val res1: Boolean = false

scala> i == l
val res2: Boolean = true

Rust

总结

TODO

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