Differences between abstract classes and interfaces

• Abstract classes can have variables that are or are not defined and we have to provide access modifiers to members in abstract classes
• In case of Interfaces all variables are public ,static and final by default so we can't provide those keywords to them and they are by default. abstract classes methods can be public ,private etc.
• Abstract classes can have constructors as well that is not possible in Interfaces.But abstract classes can never be instantiated
• Abstract class can extend only one parent class but can implement mmutiple interfaces
• Abstract can use static and non static methods and variables.Abstract classes is used to provide a common definition of a base class that multiple child classes can share
• Interfaces can't be instantiated. Neither can be abstract classes.All methods in interface are public and final.
• Interfaces can implement another interface
• Starting with Java 8, default and static methods may have implementation in the interface definition.
• In jave 9 private and private static methods were added to interfaces
• Interfaces are used to implement common behaviour when we are not concerned about who actually implements that behavior
• List interface is an example of interface where ArrayList and LinkedList implement that interface.
• When to user interface. When unrelated classes implement our interface we can use interface.
• If we have closely related classes that extend a base class we use abstract classes.