Java 断言禁用 Map.remove() 的执行

Question

您好，我正在尝试从 Map 中删除对象，并且我正在使用断言测试此操作

// definition of map 
private Map<String, Map<Long, Object>> groups = new HashMap<String, Map<Long, Object>>();

// this does not remove item from map
assert groups.get("key").remove(id) != null;

// this removes item from map 
groups.get("key").remove(id); 

上述方法在相同的数据上进行了测试。为什么 Map.remove() 不适用于断言？

Answer 1

assert 语句根据您启动 VM 的方式执行或不执行。您不应该在断言中加入副作用。

来自 section 14.10 of the Java Language Specification :

An assertion is either enabled or disabled. If the assertion is enabled, evaluation of the assertion causes evaluation of the boolean expression and an error is reported if the expression evaluates to false. If the assertion is disabled, evaluation of the assertion has no effect whatsoever.

在同一节的讨论部分:

Because assertions may be disabled, programs must not assume that the expressions contained in assertions will be evaluated. Thus, these boolean expressions should generally be free of side effects: