Inspecting Fields

The Reflection API allows dynamically querying class fields, reading values from active objects, and writing new values directly, bypassing encapsulation.

Method Differences

• getFields(): Returns only public fields, including those inherited from parent classes.
• getDeclaredFields(): Returns all fields declared in the class (public, protected, package, and private), but excludes inherited fields.
• setAccessible(true): Instructs the JVM to bypass standard access checks, allowing writes to private fields.

Code Walkthrough

This program accesses and modifies a private field using reflection.

import java.lang.reflect.Field;
class Account {
    private String id = "ACC_100";
}
public class FieldReflectionDemo {
    public static void main(String[] args) throws Exception {
        Account acc = new Account();
// Get private field by name
        Field idField = Account.class.getDeclaredField("id");
// Bypass private visibility check
        idField.setAccessible(true);
// Read value
        String value = (String) idField.get(acc);
        System.out.println("Original Private ID: " + value);
// Modify value
        idField.set(acc, "ACC_200");
        System.out.println("Modified Private ID: " + idField.get(acc));
    }
}

Interview-Relevant Information