在java中创建类的基础知识

这是一个简单的问题，但我的AP Comp Sci书并没有很好地解释它，你们总是很有用的

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在Java中创建自定义类并在该类中创建方法，然后调用这些方法的基本方法是什么。我知道这很简单，但我在任何地方都找不到一个好的解释

似乎你需要更好地理解OOP。因此，让我们创建一个类和一个测试客户机来帮助您。我们将创建一个类和一个测试客户机（或驱动程序）来计算电势。请注意，这个例子来自罗伯特·塞吉威克和凯文·韦恩（我极力推荐一本优秀的书）

首先，我们创建一个

费用
类：

/*
Separate classes must be in the same directory as main method or must invoke 
classpath
*/
public class Charge {
    // first declare instance variables which are usually private
    private final double rx;
    private final double ry;
    private final double q;

    /* A class contains constructors that are invoked to create objects from a 
    class blueprint. Constructor declarations look like method declarations 
    -except that they use the name of the class and have no return type.  
    Constructors must use the exact name of the class, case sensitive.
    Classes and Constructors are capitalized - methods are camelCase.
    */

    // Constructor
    public Charge(double x0, double y0, double q0) {
        rx = x0;
        ry = y0;
        q = q0;
    }

    /*
    The method to compute electrical potential which is defined by the equation
    V = kq/r
    */
    public double potentialAt(double x, double y) {
        double k = 8.99e09;  // Electrostatic Constant that k=8.99 X 10^9 Nm^2/C^2 (N = Newtons, m = meters, C = Coloumbs)
        // r = delta x - delta y
        double dx = x - rx; // delta x for distance
        double dy = y - ry; // delta y for distance
        return k*q/Math.sqrt(dx*dx + dy*dy); // Computation using distance formula
    }
}

这将是使用此类的API。Java编程中的一个重要概念
您不需要知道如何实现数据类型就可以使用它

公共课收费
这是构造器：

Charge(double x0, double y0, double q0)

这些是实例方法。变量之间最重要的区别是
引用类型与基元类型是指可以使用引用类型变量
调用实现数据类型操作的方法

double potentialAt(double x, double y)
String toString()

使用该类的两个部分是：

1. Create an object

    ClassName   object   =  new   ClassName (invoke Constructor)
    ---------   ------      ---   ---------  -----------------
    Charge      c        =  new    Charge     (2.2, 3.4, 7.2)

2. Use instance methods on object

    c.potentialAt(2.3, 4.2)

这将是可用于此类的客户端（或驱动程序）：

import java.util.*;

public class ChargeClient {
    public static void main(String[] args) {
        // Using a scanner object to get values
        System.out.println("Please enter an X Value");
        Scanner in = new Scanner(System.in);
        double x = in.nextDouble();
        System.out.println("Please enter a Y Value");
        double y = in.nextDouble();
        /*
        1. Instantiate objects c1 and c2

            ClassName   object   =  new   ClassName (invoke Constructor)
            ---------   ------      ---   ---------  -----------------
            Charge      c        =  new    Charge     (2.2, 3.4, 7.2)

        2. We are invoking constructor from API

            Charge(double x0, double y0, double q0)
        */
        Charge c1 = new Charge(.51, .63, 21.3);
        Charge c2 = new Charge(.13, .94, 81.9);
        // print out charge so we know what we are dealing with
        System.out.println(c1);
        System.out.println(c2);
        /*
        Here we create variables to hold the return from our potential method
        which is enacted on our c1 and c2 objects.  

        1. We call a method on an object by:

            objectName.methodName(appropriate parameters)

        */
        double v1 = c1.potentialAt(x, y);
        double v2 = c2.potentialAt(x, y);
        // Concatenate results and print them out.
        System.out.println(v1 + v2);
        System.out.println("This is the printf statement:");
        System.out.printf("%.2E\n", v1 + v2);
    }
}

. 当你在那里提问时，请始终包括你的尝试，并向我们展示你的尝试。看起来你甚至都没有搜索，因为Oracle官方文档几乎是google上所有java搜索的第一个结果。这对我帮助很大，非常感谢。