Question

我有一段看起来像这样的代码：

private void methodA(String a String b){
  Employee e1=null;
  foobar(e1,b); //line 1
  //do something
  if(e1!=null){ //line 2
    //flow1
  }else{
    //flow2
  }
}
private void foobar(Employee e, String a){
  e= new Employee();
  //do stuff
}

当我为此类运行findBugs时，它在第1行显示两个警告-

Load of known null value
The variable referenced at this point is known to be null due to an earlier check against null. Although this is valid, it might be a mistake (perhaps you intended to refer to a different variable, or perhaps the earlier check to see if the variable is null should have been a check to see if it was nonnull).

并在第2行：

Redundant nullcheck of value known to be null
This method contains a redundant check of a known null value against the constant null.

为了避免这些警告，我改为执行以下操作：

private void methodA(String a String b){
  Employee e1 = foobar(b); //line 1
  //do something
  if(e1!=null){ //line 2
    //flow1
  }else{
    //flow2
  }
}
private Employee foobar(String a){
 if("some_value".equals(a)){
  Employee e= new Employee();
  //do stuff
  return e;
  }
return null;
}

这样做可以从findbugs中删除警告，但是我的问题是此更改绝对必要，还是第一种方法会产生什么影响？

Answer 1

Employee e1=null;
foobar(e1,b);

这是不正确的，因为foobar()获得null，并且在它之后不能引用e1。因此，if(e1!=null)总是 false 。

Employee e1=null;
...
private void foobar(Employee e, String a){
  e= new Employee();
  //do stuff
}

e引用了新对象，但这是方法的局部变量。

已知为null的值的冗余nullcheck

1 个答案: