Creating Instances

Reflection allows instantiating classes dynamically using the Constructor.newInstance() API. This is the foundation of dynamic object creation in Java.

Instantiation Methods Compared

• Class.newInstance() (Deprecated): Bypasses constructor exceptions (propagates checked exceptions without declaration). It can only call the no-arg constructor, throwing an instantiation error if it doesn't exist.
• Constructor.newInstance() (Preferred): Wraps all constructor exceptions in InvocationTargetException. It can invoke constructors with any parameters, making it highly flexible.

Code Walkthrough

This program demonstrates instantiating an object using its constructor with arguments.

import java.lang.reflect.Constructor;
class User {
    private String name;
    public User(String name) { this.name = name; }
    public String getName() { return name; }
}
public class InstantiationDemo {
    public static void main(String[] args) throws Exception {
        Class clazz = User.class;
// Find constructor accepting String
        Constructor constructor = clazz.getConstructor(String.class);
// Instantiate dynamically
        User user = constructor.newInstance("Alice");
        System.out.println("User created: " + user.getName()); // Alice
    }
}

Interview-Relevant Information