爲什麼我用JOptionPane.showInputDialog得到「void無法轉換爲int」錯誤？

Question

我有這個作業，我必須使用JOptionPane來計算不同形狀的面積，但是當我使用JOptionPane.showMessageDialog時，它會變成紅色，錯誤代碼表示void不能轉換爲int。有人可以幫我弄清楚如何使用JOptionPane.showMessageDialog？

public static void areaTriangle(int base, int height) 
{ 
    System.out.println(0.5 * base * height); 
} 

public static void areaCircle(int radius, double area) 
{ 
    area = Math.PI * (radius * radius); 
    System.out.println(area); 
} 

public static void areaRectangle(int length, int width) 
{ 
    System.out.println(length * width); 
} 

public static void calcArea() 
{ 
    System.out.println("What type of area do you want to calculate?"); 
    inputStr = JOptionPane.showInputDialog("Type 1 for triangle, 2 for circle, 3 for rectangle, and 0 for none, then press ENTER."); 
    int type = Integer.parseInt(inputStr); 

    if (type == 0) 
    { 
     return; 

    } 
    else if (type == 1) 
    { 
     inputStr = JOptionPane.showInputDialog("Enter the measurement of the base, then press ENTER."); 
     int base = Integer.parseInt(inputStr); 
     inputStr = JOptionPane.showInputDialog("Enter the measurement of the height, then press ENTER."); 
     int height = Integer.parseInt(inputStr); 
     int areaT = areaTriangle (base, height); 
     JOptionPane.showMessageDialog(null, "The area of the triangle is: " + areaT); 

    } 
    else if (type == 2) 
    { 
     inputStr = JOptionPane.showInputDialog("Enter the measurement of the radius, then press ENTER."); 
     int radius = Integer.parseInt(inputStr); 
     double area = Math.PI * (radius * radius); 
     int areaC = areaCircle (radius, area); 
     JOptionPane.showMessageDialog(null, "The area of the cicle is: " + areaC); 

    } 
    else if (type == 3) 
    { 
     inputStr = JOptionPane.showInputDialog("Enter the measurement of the length, then press ENTER."); 
     int length = Integer.parseInt(inputStr); 
     inputStr = JOptionPane.showInputDialog("Enter the measurement of the width, then press ENTER."); 
     int width = Integer.parseInt(inputStr); 
     int areaR = areaRectangle(length, width); 
     JOptionPane.showMessageDialog(null, "The area of the rectangle is: " + areaR); 
    } 

} 

public static void main(String[] args) 
{ 
    calcArea(); 
} 

Answer 1

您的問題無關的JOptionPane和一切與你的area*方法

首先聲明所有的方法爲void ...

public static void areaTriangle(int base, int height) { 
    System.out.println(0.5 * base * height); 
} 

public static void areaCircle(int radius, double area) { 
    area = Math.PI * (radius * radius); 
    System.out.println(area); 
} 

public static void areaRectangle(int length, int width) { 
    System.out.println(length * width); 
} 

但你試試並在給他們打電話時給變量分配返回結果...

int areaT = areaTriangle(base, height); 
//... 
int areaC = areaCircle(radius, area); 
//... 
int areaR = areaRectangle(length, width); 

這簡直沒有任何意義。

根據你彷彿是試圖做的，你需要改變你的area*方法返回某種類型的值...

public static double areaTriangle(int base, int height) { 
    return 0.5 * base * height; 
} 

public static double areaCircle(int radius, double area) { 
    return Math.PI * (radius * radius); 
} 

public static int areaRectangle(int length, int width) { 
    return length * width; 
} 

然後你可以從方法到指定的返回值一些變量...

double areaT = areaTriangle(base, height); 
//... 
double areaC = areaCircle(radius, area); 
//... 
int areaR = areaRectangle(length, width);