Java 区域计算代码在方法名和默认构造函数之间需要分号？

我编写了一个代码，可以接受用户输入，并根据输入的尺寸计算三角形、圆形或矩形的面积。代码在方法中出现了3个错误，即在方法名和方法名后面的（）之间应该有一个分号。这不是一篇“做我的家庭作业”的帖子，但我真的找到了我能找到的所有资源，真的需要一些帮助，知道如何做。代码如下，返回错误的区域以大写字母表示

import java.util.Scanner; 

public class areacalculatorNLW
{ 
private double rektlength;
private double rektwidth;
{
    double GETREKT(){
        System.out.println("Enter the length: ");
        rektlength = scan.next();
        System.out.println("Enter the width: ");
        rektwidth = scan.next();
        double rektarea = rektlength * rektwidth;
        System.out.println(rektarea);
    }
}
private double radius;
{
    double GETCIRCLE(){
        System.out.println("Enter the radius of the circle. ");
        radius = scan.next();
        double circlearea = (radius * Math.PI) * (radius * Math.PI);
        System.out.println(circlearea);
    }
}
private double trianglelength;
private double trianglewidth;
{
    double GETTRIANGLE(){
        System.out.println("Enter the triangle length: ");
        trianglelength = scan.next();
        System.out.println("Enter the triangle width: ");
        trianglewidth = scan.next();
        trianglearea = (trianglelength * trianglewidth) / 2;
        System.out.println(trianglearea);
    }
}


public static void main(String[] args) 
{ 

    Scanner scan = new Scanner(System.in);

    System.out.println("Hello, what would you like to calculate?");
    System.out.println("Type 1 to calculate the area of a rectangle.");
    System.out.println("Type 2 to calculate the area of a circle.");
    System.out.println("Type 3 to calculate the area of a triangle.");
    System.out.println("Type 4 to exit the program.");

    int choice;
    choice = scan.nextInt();

    if(choice == 1){
        this.getrekt();
    }

    if (choice == 2){
        this.getcirlce();
    }
    if (choice == 3){
        this.gettriangle();
    }

}
}

---

不能在静态方法中使用

this

，因为它引用的是当前实例，而静态方法中不存在该实例

必须创建类的实例才能调用非静态方法：

areacalculatorNLW calc = new areacalculatorNLW ();

然后调用该实例的方法。例如：

calc.GETREKT();

此外，您还应该学习Java命名约定

---

编辑：如其他评论/答案中所述，您的方法周围还有额外的大括号，应该删除。

删除额外的括号：

{
    double GETREKT(){
        System.out.println("Enter the length: ");
        rektlength = scan.next();
        System.out.println("Enter the width: ");
        rektwidth = scan.next();
        double rektarea = rektlength * rektwidth;
        System.out.println(rektarea);
    }
}

对此

    double GETREKT(){
        System.out.println("Enter the length: ");
        rektlength = scan.next();
        System.out.println("Enter the width: ");
        rektwidth = scan.next();
        double rektarea = rektlength * rektwidth;
        System.out.println(rektarea);
    }

---

您已经放置了额外的花括号，标记如上。整个方法不需要这些；只有方法正文。

显示的代码有很多错误

使用像Eclipse这样的IDE会立即告诉您出了什么问题

一个基本的语法错误：您的方法周围有一个（额外的）{}，这是一个错误。Java中的方法类似于

public void foo() {}

而你写的

{ public void foo() {} }

理解中的一个基本错误：您的主要方法是静态方法。但是，您的其他方法不是静态的。但是，在main方法中没有类的实例，因此不能调用

this.

您可以通过使用创建实例来修复此问题

public static void main(String[] args) { 
  Scanner scan = new Scanner(System.in);
  areacalculatorNLW myInstance = new areacalculatorNLW();
  myInstance.getrekt();
  ...

除此之外，您正在使用一个变量trianglearea，您没有定义该变量，并且主方法中的扫描变量在其他方法中不可见

---

我强烈建议你找其他人一起做结对编程。您应该提高对Java基本概念的了解，否则这将需要很长时间才能正确完成。

您的代码中存在许多问题：

方法声明为返回值，但没有返回语句，请将返回值更改为void

scan.next（）返回字符串。为了将其解析为Double，请使用Double.valueOf方法

不能在静态范围内使用此选项。为了使用“this”，您必须拥有对象的实例，但是静态方法附加到类而不是实例，因此您可以在主方法内创建实例并使用它

名称区分大小写-不能将方法命名为FOO，以后再调用它

命名约定：类应以大写字母开头，方法和变量应以驼峰大小写命名，并以小写字母开头（例如myMethod而不是myMethod）

当您声明一个类时，将字段和方法聚集在一起更容易接受

您还忘记声明TriangalLearea变量

以下是修复这些问题后的代码，请尝试了解更改（为了使用此代码，您还必须更改文件名以匹配类名：

import java.util.Scanner;

public class AreaCalculator {
    private double trianglearea;
    private double rektlength;
    private double rektwidth;
    private double trianglelength;
    private double trianglewidth;

    void getRect(Scanner scan) {
        System.out.println("Enter the length: ");
        rektlength = Double.valueOf(scan.next());
        System.out.println("Enter the width: ");
        rektwidth = Double.valueOf(scan.next());
        double rektarea = rektlength * rektwidth;
        System.out.println(rektarea);
    }

    private double radius;

    void getCircle(Scanner scan) {
        System.out.println("Enter the radius of the circle. ");
        radius = Double.valueOf(scan.next());
        double circlearea = (radius * Math.PI) * (radius * Math.PI);
        System.out.println(circlearea);
    }

    void getTriangle(Scanner scan) {
        System.out.println("Enter the triangle length: ");
        trianglelength = Double.valueOf(scan.next());
        System.out.println("Enter the triangle width: ");
        trianglewidth = Double.valueOf(scan.next());
        trianglearea = (trianglelength * trianglewidth) / 2;
        System.out.println(trianglearea);
    }

    public static void main(String[] args) {

        Scanner scan = new Scanner(System.in);

        System.out.println("Hello, what would you like to calculate?");
        System.out.println("Type 1 to calculate the area of a rectangle.");
        System.out.println("Type 2 to calculate the area of a circle.");
        System.out.println("Type 3 to calculate the area of a triangle.");
        System.out.println("Type 4 to exit the program.");

        int choice;
        choice = scan.nextInt();

        AreaCalculator AreaCalculator = new AreaCalculator();

        if (choice == 1) {
            AreaCalculator.getRect(scan);
        }

        if (choice == 2) {
            AreaCalculator.getCircle(scan);
        }
        if (choice == 3) {
            AreaCalculator.getTriangle(scan);
        }

    }
}

---

我不认为这个错误是因为这个关键字。那是因为额外的括号。还是我错了？

import java.util.Scanner;

public class AreaCalculator {
    private double trianglearea;
    private double rektlength;
    private double rektwidth;
    private double trianglelength;
    private double trianglewidth;

    void getRect(Scanner scan) {
        System.out.println("Enter the length: ");
        rektlength = Double.valueOf(scan.next());
        System.out.println("Enter the width: ");
        rektwidth = Double.valueOf(scan.next());
        double rektarea = rektlength * rektwidth;
        System.out.println(rektarea);
    }

    private double radius;

    void getCircle(Scanner scan) {
        System.out.println("Enter the radius of the circle. ");
        radius = Double.valueOf(scan.next());
        double circlearea = (radius * Math.PI) * (radius * Math.PI);
        System.out.println(circlearea);
    }

    void getTriangle(Scanner scan) {
        System.out.println("Enter the triangle length: ");
        trianglelength = Double.valueOf(scan.next());
        System.out.println("Enter the triangle width: ");
        trianglewidth = Double.valueOf(scan.next());
        trianglearea = (trianglelength * trianglewidth) / 2;
        System.out.println(trianglearea);
    }

    public static void main(String[] args) {

        Scanner scan = new Scanner(System.in);

        System.out.println("Hello, what would you like to calculate?");
        System.out.println("Type 1 to calculate the area of a rectangle.");
        System.out.println("Type 2 to calculate the area of a circle.");
        System.out.println("Type 3 to calculate the area of a triangle.");
        System.out.println("Type 4 to exit the program.");

        int choice;
        choice = scan.nextInt();

        AreaCalculator AreaCalculator = new AreaCalculator();

        if (choice == 1) {
            AreaCalculator.getRect(scan);
        }

        if (choice == 2) {
            AreaCalculator.getCircle(scan);
        }
        if (choice == 3) {
            AreaCalculator.getTriangle(scan);
        }

    }
}