CODEWITHSUNDEEP
javagenerics
Koerr
Koerr

Reputation: 15733

how can I implement this method using java template?

create a interface(using template):

package util.filter;
public interface Filter<INPUT,OUTPUT> {
    public OUTPUT filter(INPUT mes);
}

and an implemented class (only for test):

package util.filter;
public static class TestImplFilter implements Filter<Integer,String>{
    public String filter(Integer i){
        return "Hello World!";
    }
}

I can using this code to test:

Filter<Integer,String> f=new TestImplFilter();
System.out.println(f.filter(123));
//output: Hello World!

now,I want create a static method,

using impl class path (util.filter.TestImplFilter) as an argument，

and INPUT as second argument, and return a OUTPUT.

so, I writed follow code:

private static Object createInstance(String classPath) {
    try {
        Class<?> tClass = Class.forName(classPath);
        if (tClass != null) {
            return tClass.newInstance();
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
    return null;
}
public final static Filter<?,?> getFilter(String path){
    return (Filter<?,?>)createInstance(path);
}

//my problem in here:
public final static OUTPUT filter(String path,INPUT mes){
    Filter<?,?> filter = (Filter<?, ?>) createInstance(path);
    return filter.filter(mes);
}

my problem in static method filter(String path,INPUT mes), this code is error.

how can I fix it and implement this method?

thanks for help :)

Upvotes: 0

Views: 411

Answers (1)

Ralph
Ralph

Reputation: 120831

my mistake, I mashed the order, now it is correct

You can specifiy generics for static methods too. To do that, add the gereric template information ahead of the return parameter:

 public final static<INPUT,OUTPUT>  OUTPUT filter(String path,INPUT mes){

then it will compile.

public class Test {
    private static Object createInstance(String classPath) {
        try {
            Class<?> tClass = Class.forName(classPath);
            if (tClass != null) {
                return tClass.newInstance();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }

    @SuppressWarnings("unchecked")
    public final static <INPUT, OUTPUT> Filter<INPUT, OUTPUT> getFilter(String path) {
        return (Filter<INPUT, OUTPUT>) createInstance(path);
    }

    public final static <INPUT, OUTPUT> OUTPUT filter(String path, INPUT mes) {
        Filter<INPUT, OUTPUT> filter = getFilter(path);
        return filter.filter(mes);
    }
}

Upvotes: 2

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