invoke_a_method.md

Invoke a Method

Just as you can get and set a field using the .get and .set methods on a Field, you can invoke a method by using the .invoke method on a Method.

For instance methods there is a first "hidden" argument that is the instance you would be invoking the method on. This needs to be the first argument to .invoke.

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

class Main {
    void main() throws IllegalAccessException, InvocationTargetException {
        Class<Tea> teaClass = Tea.class;

        // sip taking zero arguments
        Method sipMethod;
        try {
            sipMethod = teaClass.getMethod("sip", int.class);
        } catch (NoSuchMethodException e) {
            throw new RuntimeException(e);
        }

        var tea = new Tea();

        sipMethod.invoke(tea, 5);
    }
}

class Tea {
    public void sip(int numberOfSips) {
        IO.println("You made " + numberOfSips + " sips");
    }
}

For static methods you do not need an instance of the class to invoke them. Instead you need to pass the class itself as the first argument to .invoke.

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

class Main {
    void main() throws IllegalAccessException, InvocationTargetException {
        Class<Apple> appleClass = Apple.class;

        // sip taking zero arguments
        Method biteMethod;
        try {
            biteMethod = appleClass.getMethod("bite", int.class);
        } catch (NoSuchMethodException e) {
            throw new RuntimeException(e);
        }

        biteMethod.invoke(Apple.class, 5);
        biteMethod.invoke(Apple.class, 1);
    }
}

class Apple {
    public static void bite(int times) {
        IO.println("You took " + times + " bite" + (times < 1 ? "." : "s."));
    }
}