java 装箱的值被取消装箱，然后立即重新装箱
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A boxed value is unboxed and then immediately reboxed
提问by Srinivasan
I am getting the Findugs error "A boxed value is unboxed and then immediately reboxed".
我收到 Findugs 错误“一个装箱的值被取消装箱，然后立即重新装箱”。
This is the Code:
这是代码：
Employee emp = new Employee()
Long lmt = 123L;
emp.setLimit(Long.valueOf(lmt));
In this, Employee limitfield is of type Long. Could you please let me know what is the error?
在此， Employeelimit字段的类型为Long。你能告诉我是什么错误吗？
回答by Peter Butkovic
The problem is that you're converting Long-> long-> Long.
问题是您正在转换Long-> long-> Long。
So in the background:
所以在后台：
Long.valueOf(lmt)convertsLongtolongemp.setLimit(<long>);convertslongtoLongagain
Long.valueOf(lmt)转换Long为longemp.setLimit(<long>);再次转换long为Long
As of Java 5 autoboxing happens => your code should look like this:
从 Java 5 自动装箱开始 => 你的代码应该是这样的：
Employee emp = new Employee()
Long lmt = 123L;
emp.setLimit(lmt);
or even:
甚至：
Employee emp = new Employee()
long lmt = 123L;
emp.setLimit(lmt);
回答by jpkrohling
That happens because Long.valueOf(long)will unbox your lmtfrom Longto long, just to get a Longagain. As you said that limitis a Long, you don't need to use Long.valueOf, just use the var:
发生这种情况是因为Long.valueOf(long)会将您的lmtfrom拆箱Long到long，只是为了Long再次获得。至于你说的那limit是Long，你不需要使用Long.valueOf，只要使用var：
emp.setLimit(lmt);
回答by Andreas Dolk
emp.setLimit(Long.valueOf(lmt));
Long.valueOftakes a longvalue, but you pass a Longvalue -- mandating unboxing. Immediately afterward, however, Long.valueOfre-boxes the value and the expression evaluates to a Longagain. FindBugs detects the unnecessary conversion chain Long-> long-> Long.
Long.valueOf接受一个long值，但您传递一个Long值——强制拆箱。然而，紧随其后的是Long.valueOf重新装箱该值并且表达式的计算结果Long再次为 a 。FindBugs 检测到不必要的转换链Long-> long-> Long。
