#Class in Java is the basic unit for constructing object-oriented programs. It is a "template" for objects or entities formed by extracting the common attributes and methods of similar objects.
Objects in Java (Recommended learning: java course)
Now let’s take a deeper look at what an object is. If you look at the real world around you, you will find that there are many objects around you, such as cars, dogs, people, etc. All these objects have their own state and behavior.
Take a dog as an example. Its status includes: name, breed, and color. Its behaviors include: barking, wagging its tail, and running.
Comparing real objects and software objects, they are very similar.
Software objects also have state and behavior. The state of a software object is its attribute, and its behavior is reflected through methods.
In software development, methods operate on changes in the internal state of objects, and mutual calls between objects are also completed through methods.
Classes in Java
Classes can be seen as templates for creating Java objects.
Let’s understand the definition of a class in Java through the following simple class:
public class Dog{
String breed; int age; String color; void barking(){
}
void hungry(){
}
void sleeping(){
}
}A class can contain the following types of variables:
Local variables : Variables defined in methods, constructors or statement blocks are called local variables. Variable declaration and initialization are all in methods. After the method ends, the variables will be automatically destroyed.
Member variables: Member variables are variables defined in the class and outside the method body. Such variables are instantiated when the object is created. Member variables can be accessed by methods, constructors, and statement blocks of a specific class.
Class variables: Class variables are also declared in the class, outside the method body, but must be declared as static type.
A class can have multiple methods. In the above example: barking(), hungry() and sleeping() are all methods of the Dog class.
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