-Xlint:在netbeans中未选中

Question

在NetBeans中清理和构建我的项目时,会出现"不安全操作"的警告,所以我使用-Xlint:unchecked来查看这些操作,但我无法理解我做错了什么.这些是警告,然后我的代码谢谢!

UploadBean.java:40: warning: [unchecked] unchecked conversion
    private final List fileList = Collections.synchronizedList(new ArrayList());
  required: List<T>
  found:    ArrayList
  where T is a type-variable:
    T extends Object declared in method <T>synchronizedList(List<T>)


UploadBean.java:40: warning: [unchecked] unchecked method invocation: method synchronizedList in class Collections is applied to given types
    private final List fileList = Collections.synchronizedList(new ArrayList());
  required: List<T>
  found: ArrayList
  where T is a type-variable:
    T extends Object declared in method <T>synchronizedList(List<T>)


UploadBean.java:97: warning: [unchecked] unchecked call to add(E) as a member of the raw type List
                    fileList.add(fd);
  where E is a type-variable:
    E extends Object declared in interface List
3 warnings

码

 //This is line 40    
 private final List fileList = Collections.synchronizedList(new ArrayList());

 //This is line 88
 public void doUpload(FileEntryEvent e) {
        FileEntry file = (FileEntry) e.getSource();
        FileEntryResults result = file.getResults();
        for (FileInfo fileInfo : result.getFiles()) {
            if (fileInfo.isSaved()) {
                FileDescription fd =
                        new FileDescription(
                        (FileInfo) fileInfo.clone(), getIdCounter());
                synchronized (fileList) {
                    fileList.add(fd); //This is line 97
                }
            }
        }
    }

干杯

Answer 1

您需要了解Java Generics.旧的1.4样式仍然会编译,但它会发出警告(一些人认为是错误的).

由于您使用的类需要Generic Type参数,因此需要将它们指定给编译器,如下所示:

 //This is line 40    
 private final List<FileDescription> fileList = Collections.synchronizedList(new ArrayList<FileDescription>());

 //This is line 88
 public void doUpload(FileEntryEvent e) {
        FileEntry file = (FileEntry) e.getSource();
        FileEntryResults result = file.getResults();
        for (FileInfo fileInfo : result.getFiles()) {
            if (fileInfo.isSaved()) {
                FileDescription fd =
                        new FileDescription(
                        (FileInfo) fileInfo.clone(), getIdCounter());
                synchronized (fileList) {
                    fileList.add(fd); //This is line 97
                }
            }
        }
    }

请注意,对于泛型,不再需要某些类型的转换.例如,fileList.get(0)将FileDescription在上面的示例中返回a ,而无需进行显式转换.

泛型参数指示存储在其中的任何内容fileList必须是"至少"FileDescription.编译器检查是否无法在列表中放置非FileDescription项,并且输出代码实际上不执行任何运行时检查.因此,泛型实际上不会像其他语言中的类似技术那样遭受性能命中,但是编译器执行的"类型擦除"使得诸如通用参数的运行时类型分析之类的技术难以实现.

尝试一下,你会喜欢它们.

如果此代码是在Generics发布之前编写的,您可能希望使用向后兼容性标志(-source 1.4 -target 1.4)对其进行编译.