The difference between classes and objects in java

Classes are templates, objects are instances; classes define properties and methods, and objects have their own properties and states; classes are stored in the method area, and objects are stored in the heap.

The difference between classes and objects

In Java, classes and objects are object-oriented programming (OOP) Two basic concepts. The main differences between them are as follows:

Definition

• Class: is a template or blueprint used to create objects with the same properties and method object.
• Object: is an actual instance of a class, with its own data and behavior.

Creation method

• Classes are defined using the class keyword, just like a class declaration.
• Objects are created using the new keyword, which allocates memory and calls the class's constructor.

Attributes

• Class: Define the attributes (variables) of the class.
• Object: Has its own attribute values.

Method

• Class: Defines the behavior (method) of the class.
• Object: You can access and call methods of the class.

Object state

• Objects can have their own state, storing and manipulating data through their properties and methods.
• A class does not have its own state, it only provides a blueprint for the structure and behavior of the object.

Memory Management

• Class: Stored in the method area, shared by all objects created by this class.
• Object: Stored in the heap, each object has its own instance.

Example

// 定义一个类
class Person {
    int age;
    String name;
    
    // 构造函数
    public Person(int age, String name) {
        this.age = age;
        this.name = name;
    }
    
    // 方法
    public void introduce() {
        System.out.println("Hi, I am " + name + " and I am " + age + " years old.");
    }
}

// 创建一个对象
Person John = new Person(20, "John Doe");

// 访问对象属性和调用方法
John.introduce();

In the above example, the Person class defines age and name Properties and introduce() methods. A John object is an instance of the Person class, has its own age and name values, and can call introduce() method.

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