Question

我正在尝试清理一些遗留代码并发出一些unchecked cast警告我正在努力摆脱它。

我已将提取警告的代码提取到下面的可编译程序中。请注意，我删除了大部分代码以使其更小，因此所有代码可能都没有完全合理。它编译，但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.");
        }
    };
}

编译上面的代码会发出以下警告

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

更改

public <TEntry extends Entry> TEntry createEntry...

到

public <TEntry extends Entry<T>> TEntry createEntry...

给出编译器错误（cannot find symbol: class T）。

我不想太多地更改代码，因为它工作正常，所以我如何修改（不隐藏）代码更改最少的警告？

Answer 1

如果要使用多个通用参数，则需要在参数列表中指定它。你能试试吗？

public <T, TEntry extends Entry<T>> TEntry createEntry(...

<强>更新

我有时间玩这个并且使用那些漂亮的类对象：

    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);
    }
}

Answer 2

您已将Class对象传递给方法，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);
}

上述更改会使您的代码在没有警告的情况下编译。

此外，<T>签名中的getInputStream()可能不是必需的。

Answer 3

对于遗留代码的恕我直言，为了使它通用友好可以是一种非常好的体验，特别是如果你有大量的代码...因为可能已经部署了这个代码，你会不会考虑迭代方法？

通过迭代方法，我的意思是......获取所有警告并使用@SuppressWarning消除它们，然后使用TODO注释，随着时间的推移，每次需要对代码进行更改时，如果您绊倒在TODO上，然后改变它......

我只是说你刚刚迁移到Java 5并且有成千上万的警告..

困难的未经检查的投射警告

3 个答案: