I'm a little lost here! Can someone give me a hint?

Question about the task

What is ClassLoader?

Java Collections, Level 5, Lesson 10

Under discussion

Implement the getAllAnimals method.
The method's pathToAnimals parameter is the absolute path to the directory where the compiled classes are saved.
The path doesn't necessarily have a "/" at the end.
Not all classes inherit the Animal interface.
Not all classes have a public no-argument constructor.
Only for classes that both inherit Animal and have a public no-argument constructor, create one object each.
Add the created objects to the resulting set and return it.
The main method is not tested.

Requirements:

The size of the set returned by the getAllAnimals method must be equal to the number of classes that both support the Animal interface and have a public no-argument constructor (from among the classes found in the directory passed as an argument).
The set returned by the getAllAnimals method must include all of the classes that both support the Animal interface and have a public no-argument constructor (from among the classes found in the directory passed as an argument).
The set returned by the getAllAnimals method must NOT contain any classes that don't both support the Animal interface and have a public no-argument constructor (from among the classes found in the directory passed as an argument).
The getAllAnimals method must be static.

package com.codegym.task.task35.task3507; import java.io.File; import java.util.HashSet; import java.util.List; import java.util.Set; /* What is ClassLoader? */ public class Solution { public static void main(String[] args) throws ClassNotFoundException { Set<? extends Animal> allAnimals = getAllAnimals(Solution.class.getProtectionDomain().getCodeSource().getLocation().getPath() + Solution.class.getPackage().getName().replaceAll("[.]", "/") + "/data"); System.out.println(allAnimals); } public static <T extends Animal> Set<T> getAllAnimals(String pathToAnimals) throws ClassNotFoundException { Set<T> set = new HashSet<>(); ClassLoader loader = new ClassLoader() { @Override public Class<?> loadClass(String name) throws ClassNotFoundException { return super.loadClass(name); } }; File file = new File(pathToAnimals); String[] classFiles = file.list(); for (String fileName : classFiles){ Object fileClass = loader.loadClass(fileName); if (fileClass instanceof Animal){ set.add((T)fileClass); } } return set; } }

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JianQiu Hwang

Level 35 , Washington

19 April 2020, 01:07

You should build your own `loadClass` method instead of `return super.loadClass(name);`, and you should check the classes before add it to set. Here the example:

public static Set<? extends Animal> getAllAnimals(String pathToAnimals) {
    Set<Animal> set = new HashSet<>();
    File[] files = new File(pathToAnimals).listFiles();
    ClassLoader classLoader = new ClassLoader() {
        @Override
        public Class<?> findClass(String name) throws ClassNotFoundException {
            try {
                File file = new File(name);
                byte[] byteArray = Files.readAllBytes(new File(name).toPath());
                String s = Solution.class.getPackage().getName() + ".data." +
                        file.getName().substring(0, file.getName().length() -".class".length());
                return defineClass(s, byteArray, 0, byteArray.length);
            } catch (Exception e) {
                e.printStackTrace();
            }
            return super.findClass(name);
        }
    };
    for (File file : files) {
        if (file.isFile() && file.getName().endsWith(".class")) {
            Class clazz = null;
            try {
                clazz = classLoader.loadClass(file.getPath());
                Constructor ct = clazz.getConstructor();
                if (Modifier.isPublic(ct.getModifiers()) && Animal.class.isAssignableFrom(clazz)) {
                    Animal animal = (Animal) clazz.newInstance();
                    set.add(animal);
                }
            } catch (NoSuchMethodException | IllegalAccessException | InstantiationException | ClassNotFoundException ignored) {
            }
        }
    }
    return set;
}