An abstract class can have both abstract methods (methods without a body) and concrete methods (methods with a body), whereas an interface can only have abstract methods (though from Java 8 onwards, interfaces can also have default and static methods with a body). An abstract class can have instance variables, constructors, and can provide implementations for some methods, while an interface cannot have instance variables or constructors and is meant purely for defining a contract that implementing classes must follow. A class can extend only one abstract class but can implement multiple interfaces.