JAVA - Creating an instance of an object in a class?

Question

So,

I have a class called "Geraform" that I need to return a HTML-style string with some information contained in an annotation. I got the code to work when I pass a certain class to it, but I would like the code, before returning to String, to create an instance of a class object so that I could read the annotations of the methods of that object and generate the HTML form.

What happens is that when I get the value of the fields in the annotation, for example

String label = annotation.label(); 

I’m getting a nullPointerException, which I think is the lack of an object.

My note Campo.java:

import java.lang.annotation.Retention;
import java.lang.annotation.Target;
import java.lang.annotation.ElementType;
import java.lang.annotation.RetentionPolicy;

@Target( { ElementType.METHOD } )
@Retention( RetentionPolicy.RUNTIME )
public @interface Campo {

    int maxLength() default 0;

    boolean required() default false;

    String label();

}

My class Geraform.Java:

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

public class GeraForm {

    public String incluir(Class<?> formClass) throws NoSuchMethodException, SecurityException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
        Class<?> wantedClass = formClass;
        Method[] classMethods = wantedClass.getDeclaredMethods();
        String methodName = "temp";

        //I need to return a String in HTML form style at the and of the method
        //Im gonna construct the string piece by piece to return at the end of the method
        String returnString = "a";

        //I get the name of the method and put it to lower case
        for(int i=0; i < classMethods.length; i++) {
            if(classMethods[i].getName().startsWith("set")) {
                methodName = classMethods[i].getName().substring(3, classMethods[i].getName().length()).toLowerCase();
            }
        }

        Campo annotation = classMethods[0].getAnnotation(Campo.class);

        //Here I get the value of every field in the annotation
        String label = annotation.label(); 
        int maxLength = annotation.maxLength();
        boolean required = annotation.required();

        returnString = label+"<input type=\"text\" name=\""+methodName+"\"";
       if(maxLength != 0) {
           returnString = returnString +" maxlength=\""+maxLength+"\"";
       }
        if(required == true) {
            returnString = returnString + " required=\"" + required + "\"";
        }

        returnString = returnString + ">";


        return returnString;
    }

}

Answer 1

The problem is not the lack of instance.

So that the line

String label = annotation.label();

throw a NullPointerException, the return of the method called in

Campo annotation = classMethods[0].getAnnotation(Campo.class);

must be void.

According to the documentation of the method, it returns null if the desired annotation is not present in the method in question.

Thus, it is very likely that the problem is caused by the fact that the method is in the first position of classMethods[] not being annotated with the annotation @Campo.

---

EDIT:

Answering the question (even if it is not the cause of the problem): to create a new instance from Class<?> wantedClass you can do:

wantedClass.newInstance();

It is worth remembering that this method launches a IllegalAccessException.