Method Overriding Summary

Object Class

• Every class implicitly inherits from Object
• Object provides common methods:
  • equals(Object obj): Check equality
  • toString(): String representation
  • hashCode(): Hash value
  • Others like clone(), finalize()

Method Overriding

• Subclass provides new implementation of parent's method
• Must have same method descriptor as parent
• Enables polymorphic behavior
• Example:

  class Circle {
    @Override
    public String toString() {
      return "Circle with radius " + this.r;
    }
  }
  

Rules for Overriding

• Method must have:
  • Same name
  • Same parameters (number, type, order)
  • Same return type (or covariant)
  • Same or less restrictive access
• Cannot override:
  • final methods
  • static methods
  • private methods

@Override Annotation

• Indicates method is meant to override
• Helps catch errors at compile time
• Best practice to always use it
• Example:

  @Override  // Compiler checks if parent has this method
  public boolean equals(Object obj) {
    // implementation
  }
  

Using super with Overridden Methods

• Access parent's version using super
• Useful when extending behavior
• Example:

  @Override
  public String toString() {
    return super.toString() + " (custom info)";
  }
  

Common Methods to Override

• toString(): String representation
• equals(Object): Object equality
• hashCode(): Hash code for hash-based collections
• Example:

  @Override
  public boolean equals(Object obj) {
    if (obj instanceof Circle) {
      Circle other = (Circle) obj;
      return this.radius == other.radius;
    }
    return false;
  }
  

Best Practices

• Always use @Override annotation
• Override toString() for debugging
• Override equals() and hashCode() together
• Keep overridden methods consistent with parent's contract
• Document overridden behavior