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在Java中转换为泛型类型时的警告

warnings generics java

L. Cornelius Dol · 技术社区 · 16 年前

我有一些通用代码,我无法弄清楚如何合法地防止收到来自的警告;我目前正在使用@suppresswarnings(“unchecked”),因为在没有警告的情况下,强制转换通用类型似乎无法完成。

我怎样才能去掉注释?

我拥有的是:

public MyObject(SharedContext<Object> ctx) {
    super(ctx); // set protected field 'context'
    ...
    context.set("Input Fields"  ,Collections.synchronizedMap(new TreeMap<String,Pair<String,Boolean>>(String.CASE_INSENSITIVE_ORDER)));
    context.set("Output Fields" ,Collections.synchronizedMap(new TreeMap<String,String>              (String.CASE_INSENSITIVE_ORDER)));
    context.set("Event Registry",new EventRegistry(log)                                                                              );
    }

@SuppressWarnings("unchecked")
protected void startup() {
    inputFields     =(Map<String,Pair<String,Boolean>>)context.get("Input Fields"  ,null);
    outputFields    =(Map<String,String>              )context.get("Output Fields" ,null);
    eventRegistry   =(EventRegistry                   )context.get("Event Registry",null);
    ...
    }

受保护的变量上下文是类型 SharedContext<Object> .

如果没有注释,编译器将发出警告:

...\MyClass.java:94: warning: [unchecked] unchecked cast
found   : java.lang.Object
required: java.util.Map<java.lang.String,com.mycompany.Pair<java.lang.String,java.lang.Boolean>>
    inputFields     =(Map<String,Pair<String,Boolean>>)context.get("Input Fields"  ,null);
                                                                  ^
...\MyClass.java:95: warning: [unchecked] unchecked cast
found   : java.lang.Object
required: java.util.Map<java.lang.String,java.lang.String>
    outputFields    =(Map<String,String>              )context.get("Output Fields" ,null);

5 回复 | 直到 16 年前

L. Cornelius Dol 16 年前

public class Generics
{

static public void main(String[] args) {
    Generics.test();
    }

static private void test() {
    Map<String,Object> ctx=new TreeMap<String,Object>();
    Map<String,Object> map=new TreeMap<String,Object>();
    Map<String,Object> tst;

    ctx.put("Test",map);
    tst=uncheckedCast(ctx.get("Test"));
    }

@SuppressWarnings({"unchecked"})
static public <T> T uncheckedCast(Object obj) {
    return (T)obj;
    }

}

@SuppressWarnings("unchecked") 
public static <T, X extends T> X uncheckedCast(T o) {
    return (X) o;
    }

protected void startup() {
    inputFields  =GenUtil.uncheckedCast(context.get("Input Fields"  ,null));
    outputFields =GenUtil.uncheckedCast(context.get("Output Fields" ,null));
    eventRegistry=GenUtil.uncheckedCast(context.get("Event Registry",null));
    ...
    }

finnw 16 年前

Map<String, Pair<String, Boolean>> SharedContext TreeMap ForwardingMap Guava

class InputFieldMap extends ForwardingMap<String,Pair<String,Boolean>> {

    private final Map<String,Pair<String,Boolean>> delegate =
        Maps.newTreeMap(String.CASE_INSENSITIVE_ORDER);
    protected Map<String,Pair<String,Boolean>> delegate() { return delegate; }

}

// ...

context.set("Input Fields"  ,Collections.synchronizedMap(new InputFieldMap()));

// ...

inputFields     =(InputFieldMap)context.get("Input Fields"  ,null);
outputFields    =(Map<?,?>     )context.get("Output Fields" ,null);

String bar = String.valueOf(outputFields.get("foo"));

Map<?, String> wrappedOutputFields    =
    Maps.transformValues(outputFields, Functions.toStringFunction());

// ...

String bar = wrappedOutputFields.get("foo");

Steve McLeod 16 年前

context.setInputFields(...)
context.setOutputFields(...)
context.setEventRegistry(...)
context.getInputFields()
etc.

Amir Afghani 16 年前

context

SharedContext<Object>

Adisesha 16 年前

http://java.sun.com/javase/6/docs/technotes/tools/windows/javac.html