[英]Difficult unchecked cast warnings
我正在尝试清理一些旧代码,并尝试消除一些unchecked cast
强制转换警告。
我将给出警告的代码提取到下面的可编译程序中。 请注意,我删除了许多代码以使其更小,因此所有这些代码可能都不完全有意义。 它可以编译,但是运行它不会做任何事情。
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.List;
import java.util.zip.ZipEntry;
import java.util.zip.ZipException;
import java.util.zip.ZipInputStream;
public class GenericsTest {
public static void main(String[] args) throws IOException {
Reader reader = new Reader();
List<String> stringEntries = reader.readAll(StringEntry.class);
}
public static class Reader {
public <T> ZipInputStream getInputStream(String fileName) throws ZipException, FileNotFoundException {
return new ZipInputStream(new FileInputStream(fileName));//_file.getInputStream(_paths.get(fileName));
}
public <T, TEntry extends Entry<T>> List<T> readAll(Class<TEntry> type) throws IOException {
List<T> list = new ArrayList<T>();
List<TEntry> entries = createEntries(type);
for (TEntry entry : entries) {
list.add(read(entry));
}
return list;
}
public <T> T read(Entry<T> entry) throws IOException {
ZipInputStream is = null;
try {
//is = _archive.getInputStream(entry.getName());
return entry.read(is);
} finally {
if (is != null) {
is.close();
}
}
}
public <TEntry extends Entry> List<TEntry> createEntries(Class<TEntry> type) throws ZipException {
List<TEntry> entries = new ArrayList<TEntry>();
List<String> paths = new ArrayList<String>();//getPaths(type);
for (String path : paths) {
entries.add(createEntry(type, path));
}
return entries;
}
public <TEntry extends Entry> TEntry createEntry(Class<TEntry> type, String folder) {
if (StringEntry.class.equals(type)) {
return (TEntry) new StringEntry(folder);
} else if (IntegerEntry.class.equals(type)) {
return (TEntry) new IntegerEntry(folder);
}
throw new IllegalArgumentException("Unknown type: " + type);
}
}
public static abstract class Entry<T> extends ZipEntry {
private T _data;
public Entry(T data, String folder, String name) {
super(folder + "/" + name);
_data = data;
}
protected abstract T read(InputStream is) throws IOException;
};
public static class StringEntry extends Entry<String> {
public StringEntry(String folder) {
super("Hallo world!", folder, "StringEntry");
}
@Override
protected String read(InputStream is) throws IOException {
throw new UnsupportedOperationException("Not supported yet.");
}
};
public static class IntegerEntry extends Entry<Integer> {
public IntegerEntry(String folder) {
super(42, folder, "IntegerEntry");
}
@Override
protected Integer read(InputStream is) throws IOException {
throw new UnsupportedOperationException("Not supported yet.");
}
};
}
编译以上代码会给出以下警告
GenericsTest.java:57: warning: [unchecked] unchecked cast
found: GenericsTest.StringEntry
required: TEntry
return (TEntry) new StringEntry(folder);
GenericsTest.java:59: warning: [unchecked] unchecked cast
found: GenericsTest.IntegerEntry
required: TEntry
return (TEntry) new IntegerEntry(folder);
2 warnings
改变中
public <TEntry extends Entry> TEntry createEntry...
至
public <TEntry extends Entry<T>> TEntry createEntry...
给出编译器错误( cannot find symbol: class T
)。
我不想对代码进行太多更改,因为它可以正常工作,那么如何在代码更改最少的情况下修复(而不是隐藏)警告?
如果要使用多个通用参数,则需要在参数列表中指定它。 你可以试试这个吗?
public <T, TEntry extends Entry<T>> TEntry createEntry(...
更新
我花了一些时间来处理这个问题,并使用了那些不错的类对象:
public <T, TEntry extends Entry<T>> List<TEntry> createEntries(Class<TEntry> type) throws ZipException {
List<TEntry> entries = new ArrayList<TEntry>();
List<String> paths = new ArrayList<String>();//getPaths(type);
for (String path : paths) {
entries.add(createEntry(type, path));
}
return entries;
}
public <T, TEntry extends Entry<T>> TEntry createEntry(Class<TEntry> type, String folder) {
if (StringEntry.class.equals(type)) {
return type.cast(new StringEntry(folder));
} else if (IntegerEntry.class.equals(type)) {
return type.cast(new IntegerEntry(folder));
}
throw new IllegalArgumentException("Unknown type: " + type);
}
}
您已经将Class
对象传递到方法中,只需使用Class.cast()
:
public <TEntry extends Entry<?>> TEntry createEntry(Class<TEntry> type, String folder) {
if (StringEntry.class.equals(type)) {
return type.cast(new StringEntry(folder));
} else if (IntegerEntry.class.equals(type)) {
return type.cast(new IntegerEntry(folder));
}
throw new IllegalArgumentException("Unknown type: " + type);
}
上面的更改使您的代码在没有警告的情况下进行编译。
另外, getInputStream()
签名中的<T>
可能不是必需的。
对于旧代码的恕我直言,使其具有通用友好性可以是一种很好的体验,特别是如果您有大量的代码基础...由于可能已部署了此代码,您是否不考虑采用迭代方法?
用迭代的方法,我的意思是...得到所有警告,并通过@SuppressWarning和TODO注释将其消除,然后,随着时间的流逝,每次您需要更改代码时,如果偶然发现了TODO, ,然后更改它即可...
我只是说,以防您刚迁移到Java 5并收到数千条警告。
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