Question

I am trying pass class as value in hashmap. I need to get the class(value) using particular key and instantiate an object for the retrieved class. but in order to create object, i need to pass parameters.

My flow goes here, when i call the getExpo method from another class passing the key value. using the key value, i need to get the correct class and using that class need to instantiate the object and need to return the object. Inorder to create object, i need to pass the arguments since the class doesnot have default constructors.

The purpose of this procedure is in future, i need to add another key ,pair value, i shouldnot do any change……..the implementation is same for all class ie creating the object

My class goes here

public class ExampleFactory {

    static {
        HashMap<String,Class<?>> hmap = new HashMap<String,Class<?>>();

        hmap.put("jxpath", JXPathExpression.class);
        hmap.put("spel", SpelExpression.class);
    }

    public Predicate getExpo(String key,String expression) {

        // Need to get the class using key value and instantiate the object for the class
        // but i need to pass parameters in order to create the object.something like this

        //JXPathExpression object = new JXPathExpression(expression);
        return null;
    }
}

Answer 1

Try

Class aClass = hmap.get(key);
Constructor constructor = aClass.getConstructor(new Class[]{String.class});
return (Predicate) constructor.newInstance(expression);