How to use @SuppressWarning("unchecked") to specific lines of code and not into method level

Question

I have a function created where i have used @SuppressWarning("unchecked") at method level and it works as expected but i need to move this @SuppressWarning("unchecked") to only those lines of code where the warning is coming in and not at method level:

public static <T> T marshal(Class<T> cls , String xml){
      T res;
      if(cls == xml.getClass()){
          res=(T) xml;--->Need to use @SuppressWarning("unchecked") before this line
      }else{
         JAXBContext ct= JAXBContext.newInstance(cls);
         Unmarshal marshal=ctx.createUnmarshller();
         res=(T)marshal.unmarshal(new StringReader(xml));-->Need to use @SuppressWarning("unchecked") before this line
      }
      return res;
     }

In the above function I have to use @SuppressWarning("unchecked") after if and else because these are the places where warnings are shown.

Simply put `@SuppressWarnings("unchecked") final T uncheckedXml = (T) xml;` right before the assignment of `res = uncheckedXml;` for the "true" case, and similar for the second "else" one. — terrorrussia-keeps-killing, Dec 17 '20 at 15:08
Related (but specific to IntelliJ): https://stackoverflow.com/questions/7798908/disable-warning-in-intellij-for-one-line — Hulk, Dec 17 '20 at 15:11

Hulk · Answer 1 · 2020-12-17T16:37:16.923

0

Java annotations can only be placed at certain constructs, which are enumerated in ElementType, which is used when specifying where an annotation can be used (in @Target()). SuppressWarnings specifically is declared with:

@Target({TYPE,FIELD,METHOD,PARAMETER,CONSTRUCTOR,LOCAL_VARIABLE,MODULE})
@Retention(SOURCE)
public @interface SuppressWarnings

Which means it can be placed on one of these declaration contexts. So as @fluffy proposed in the comments, one way to introduce such a context the annotation can be placed at is to introduce a local variable:

@SuppressWarnings("unchecked") 
final T uncheckedXml = (T) xml;

res = uncheckedXml;

edited Dec 17 '20 at 16:37

answered Dec 17 '20 at 15:41

Hulk

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I can't edit your answer because of the "min-6 characters to change" rule, but casting to `T` in the `res = (T) uncheckedXml` is redundant and may be removed. – terrorrussia-keeps-killing Dec 17 '20 at 16:27

score 0 · Answer 2 · answered Dec 17 '20 at 17:10

You could use a generic method to handle @SuppressWarning("unchecked") when appropriate, so defined like:

@SuppressWarnings("unchecked")
public <C> C cast(Object o) {
    return (C) o;
}

However, when you use it and want to have checks you need to check for possible ClassCastException upon assignment (see this). So like:

try {
    res = cast(xml);
} catch (ClassCastException cce) {
    // a bug, help!
}

How to use @SuppressWarning("unchecked") to specific lines of code and not into method level

2 Answers2