What is method overriding?

Method overriding allows a subclass to provide a specific implementation for a method that is already defined in its parent class. The subclass method has the same name, return type, and parameter list as the parent method. Rules: method must have same name and signature; return type must be the same or a covariant (subtype of parent's return type); access modifier can be same or more permissive (can't restrict access); cannot override static methods (they can be hidden, not overridden). Example: class Payment { public String processPayment(double amount) { return "Processing payment of $" + amount; } public double calculateFee(double amount) { return amount * 0.02; // 2% fee } } class CreditCardPayment extends Payment { @Override public String processPayment(double amount) { // Custom implementation double fee = calculateFee(amount); return "Processing credit card payment of $" + amount + " (Fee: $" + fee + ")"; } @Override public double calculateFee(double amount) { return amount * 0.03; // Credit cards: 3% fee } } class PayPalPayment extends Payment { @Override public String processPayment(double amount) { return "Processing PayPal payment of $" + amount; } // No override of calculateFee -- uses parent's 2% } // Polymorphism: Payment p = new CreditCardPayment(); p.processPayment(100); // Calls CreditCardPayment's version p.calculateFee(100); // Returns 3.0. super in override: call parent's original method from override: @Override public String processPayment(double amount) { String parentResult = super.processPayment(amount); return parentResult + " [Credit Card]"; }. final methods: cannot be overridden — use for security or performance. @Override annotation verifies override is correct at compile time — always use it.