How to write classes in java

Classes in Java: Classes define data members (fields) and methods (behavior). Data members store data and methods define behavior. Class access modifiers (public, protected, default, private) specify visibility. Instantiate a class using the new operator. Classes are blueprints and objects are instances, with their own copies of data members. Inheritance allows classes to inherit fields and methods from parent classes, enabling code reuse. Classes organize code, separate data and behavior, and increase flexibility.

Classes in Java

In Java, classes are the basic building blocks used to encapsulate data and behavior . Each class defines a set of data members (called fields) and a set of methods (behaviors).

Class syntax

The following is the general syntax of a Java class:

<code class="java">class ClassName {
    // 数据成员
    private int field1;
    private String field2;

    // 方法
    public void method1() {
        // 方法体
    }

    public int method2(int a, int b) {
        // 方法体
        return a + b;
    }
}</code>

Class members

• Data members (fields): Variables that store data, which can be basic types (such as int, String) or object references.
• Method: A function that defines class behavior, can accept parameters and return results.

Class access permissions

Access permission modifiers specify the visibility of class members to other classes:

• public: accessible to all classes.
• protected: Classes or subclasses in the same package can be accessed.
• default (Package private): Only classes in the same package can access it.
• private: Only the current class can access.

Class Instantiation

To create an instance of a class, use the new operator:

<code class="java">ClassName objectName = new ClassName();</code>

Classes and Objects

A class is a blueprint or template, and an object is an instance of a class. A class can create any number of objects, each with its own copy of its data members.

Class inheritance

Java supports class inheritance, which means that a class can be derived from another class (called a parent class) and inherit its fields and methods. This allows code reuse and polymorphism.

Use classes

Classes are used to organize and encapsulate code, improving program clarity and maintainability. They also allow separation between data and behavior, increasing flexibility.

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