reflect

package one;

public class A {
    private int age;

    public A(int age) {
        this.age = age;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

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

public class B {

    public static void main(String[] args) {
        A a = new A(10);
        Class clazz = a.getClass();

        try {
            System.out.println(a.getAge());
            Method setMethod = clazz.getDeclaredMethod("setAge", new Class[] { int.class });
            setMethod.invoke(a, new Object[] { Integer.valueOf(999) });
            System.out.println(a.getAge());

            Method getMethod = clazz.getDeclaredMethod("getAge", new Class[] {});
            Integer age = (Integer) getMethod.invoke(a, new Object[] {});
            System.out.println("---" + age.intValue());
        } catch (NoSuchMethodException e) {
            e.printStackTrace();
        } catch (SecurityException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        } catch (IllegalArgumentException e) {
            e.printStackTrace();
        } catch (InvocationTargetException e) {
            e.printStackTrace();
        }
    }    
}