Scala object

1.1 What is? Scala Singleton objects in ？

Single case , Single case , seeing the name of a thing one thinks of its function , It has only one instance , There is no more . This is what distinguishes it from class Class place .

Scala Is an object-oriented programming language , Constant / Variable / Methods, etc. must be defined in class or object Just inside , It cannot be defined elsewhere . That is to say object object 、class A class is the only place where its members can be defined .

The key to define the object is object, It's an example , Not a blueprint , Therefore, it does not need external calls to execute its methods .

Like lazy variables , Singleton objects are created late , When it is first used, create .

Of course, you can create multiple singleton objects , You can also define objects in classes or methods , Naturally, you can also reference methods or constants in another object in one object or class . If you want to reference the method of an object in another script in one script , You need to import The path of the incoming object .

Be careful ： A singleton object is globally unique , So it has a stable path . That is, you cannot create two objects with the same name , No longer the same path , Not anywhere .

1.2 Why choose singleton ？

Every program needs a point from execution . stay OOPS in , Classes need objects to execute . But it needs to be implemented first main() Method to call other members of the class .

In order to be in scala In the implementation of main() Method , Many object-oriented programming languages use static keyword , however scala Not in the programming language static keyword .

Is that why Scala In, we use the definition main Method .

1.3 Characteristics of singleton objects (Features of singleton object)

Use object Keyword creation .

The members in the object are global members , That is, members can be called from anywhere in the program .

A singleton object cannot create an instance . That is, it can only have a unique instance is itself .

Allow to inherit , That is, inheritance can extend classes and features . （it can extend class and traits.）

If you want to reference in a singleton object Members in another singleton object , We will use $The\; name\; of\; the\; reference\; singleton\; object.${ Member name } The method of quoting .

---

---

---

Reference material ：
9、Scala object object