Reflection API

Reflection allows you to inspect and manipulate classes at runtime.

Getting Class Object

// Three ways
Class<?> cls1 = String.class;
Class<?> cls2 = "Hello".getClass();
Class<?> cls3 = Class.forName("java.lang.String");

Inspecting Class Members

Fields

Class<?> cls = MyClass.class;
Field[] fields = cls.getDeclaredFields();
for (Field field : fields) {
    System.out.println(field.getName());
}

Methods

Method[] methods = cls.getDeclaredMethods();
for (Method method : methods) {
    System.out.println(method.getName());
}

Constructors

Constructor<?>[] constructors = cls.getDeclaredConstructors();

Accessing Private Members

class Person {
    private String name = "Secret";
}

// Access private field
Field field = Person.class.getDeclaredField("name");
field.setAccessible(true); // Bypass private access
Person person = new Person();
String value = (String) field.get(person);
System.out.println(value); // "Secret"

Invoking Methods Dynamically

Method method = MyClass.class.getMethod("myMethod", String.class);
Object result = method.invoke(objectInstance, "parameter");

Use Cases

[!WARNING] Reflection is powerful but slow and can break encapsulation. Use sparingly!

Quiz