Differences between extends and implements

Extends can be understood as fully inheriting the features of the parent class. implements can be understood as adding some additional features to this class.

For example, Animal is a parent class, cat, dog, bird, insect all extends Animal, but cat, dog, bird can also implements such as run, shout interfaces, bird, insect can implements such as fly Interfaces

Extends is an inherited parent class. As long as the class is not declared as final or defined as abstract, it can be inherited. JAVA does not support multiple inheritance, but can be implemented using interfaces, extends can inherit only one class, and implements can implement multiple interfaces.
For example, class A extends B implements C, D, E
Interface defines some methods and is not implemented. implements is required for implementation.
Extend can inherit an interface, but it is still an interface and can be used only after implements.
For class, extends is used to (single) inherit a class, while implements is used to implement an interface ). The interface is introduced to partially provide the multi-inheritance function. In the interface, you only need to declare the method header and leave the method body to the implemented class. These implemented class instances can be treated as interface instances. You can also declare an extends (Multi-inheritance) Relationship between interfaces. Note that one interface can be extends with multiple other interfaces.