How Can I Pass a Class as a Parameter in Java?

How do I pass a class as a parameter in Java and invoke its methods?

void main() {
    callClass(MyClass.class);
}

void callClass(Class<?> classObject) throws Exception {
    Object instance = classObject.getDeclaredConstructor().newInstance();
    Method method = classObject.getMethod("someFunction");
    method.invoke(instance);
}

In Java, you can pass a Class object as a parameter to a method to invoke methods via reflection, even though reflection is limited in some environments like the Google Web Toolkit (GWT). However, GWT does not support Java reflection, making it necessary to adopt alternative approaches such as utilizing interfaces or factory patterns.

public interface RunnableClass {
    void execute();
}

public class MyClass implements RunnableClass {
    public void execute() {
        System.out.println("Executing from MyClass!");
    }
}

void callRunnable(RunnableClass runnable) {
    runnable.execute();
}

Causes

• The Google Web Toolkit does not support Java reflection, which restricts the ability to use class types dynamically at runtime.
• Attempting to instantiate classes dynamically can lead to complications if the class does not have a default constructor.

Solutions

• Use interfaces or abstract classes to define a contract for the behavior you want to implement, thereby allowing you to pass instances that conform to those contracts.
• Implement factory patterns to encapsulate the creation of class instances within a controlled environment.

Mistake: Trying to instantiate classes dynamically using reflection in GWT.

Solution: Instead, use interfaces or abstract classes to create instances.

Mistake: Forgetting to handle exceptions when invoking methods reflectively.

Solution: Always use try-catch blocks or declare your method to throw exceptions.