我试图理解为什么我收到“String 似乎与 String[] 无关”

Question

我正在创建一个项目，其中某些形状的面积或体积是使用 java 中的下拉菜单计算的。我在编译时没有任何错误，但是我收到消息“不太可能是 equals() 的参数类型：String 似乎是与 String[] 无关”。 如前所述，它符合要求，但在运行时它允许选择面积/体积，但它没有到达下一个选项窗格 select 形状。

该消息出现在：if (choices.equals("Area")) 和：if (choices.equals("Volume"))

`

import javax.swing.JOptionPane;
public class Shapes 
{
    public static void main(String[] args)
    {

//Dropdown menu for area and volume
        String[] choices = {"Area", "Volume"};
        String question = (String) JOptionPane.showInputDialog(null, "What would you like to calculate?",
            "Shapes", JOptionPane.QUESTION_MESSAGE, null,
            choices,
            choices[0]);
        System.out.println(question);

        if (choices.equals("Area"))
        {
//user chooses area
            String[] choices2D = {"triangle", "parallelogram", "rectangle", "trapezoid", "circle"};
            String question2D = (String) JOptionPane.showInputDialog(null, "What shape will you choose?",
                "Shapes", JOptionPane.QUESTION_MESSAGE, null,
                choices2D,
                choices2D[0]);
            System.out.println(question2D);
        }
//user chooses volume
        if (choices.equals("Volume"))
        {
            String[] choices3D = {"cone", "cylinder", "rectanglular prism", "trapezoid prism", "sphere"};
            String question3D = (String) JOptionPane.showInputDialog(null, "What figure will you choose?",
                "Shapes", JOptionPane.QUESTION_MESSAGE, null,
                choices3D,
                choices3D[0]);
            System.out.println(question3D);
        }
    }
}

`

我最初将选项链接到一个开关，但会不断出错，将其更改为 if 语句后，它将编译但无法正常运行。

Answer 1

您的比较是choices.equals(…) ，但您的意思是比较来自保管箱的选择，并且存储在question中。 所以比较应该是question.equals(…) 。

或者，试试这个：

import javax.swing.JOptionPane;
public class Shapes 
{
    public static void main(String... args)
    {
        //Dropdown menu for area and volume
        String[] choices = {"Area", "Volume"};
        String question = (String) JOptionPane.showInputDialog( null, 
            "What would you like to calculate?",
            "Shapes", 
            JOptionPane.QUESTION_MESSAGE, 
            null,
            choices,
            choices[0]) ;
        System.out.println(question);

        switch( question )
        {
            case "Area":
            {
                //user chooses area
                String[] choices2D = {"triangle", "parallelogram", "rectangle", "trapezoid", "circle"};
                String question2D = (String) JOptionPane.showInputDialog( null,
                    "What shape will you choose?",
                    "Shapes", 
                    JOptionPane.QUESTION_MESSAGE, 
                    null,
                    choices2D,
                    choices2D[0] );
                System.out.println( question2D );
                break;
            }

            case "Volume":
            {
                //user chooses volume
                String[] choices3D = {"cone", "cylinder", "rectanglular prism", "trapezoid prism", "sphere"};
                String question3D = (String) JOptionPane.showInputDialog( null, 
                    "What figure will you choose?",
                    "Shapes", 
                    JOptionPane.QUESTION_MESSAGE, 
                    null,
                    choices3D,
                    choices3D[0] );
                System.out.println( question3D );
                break;
            }
        }
    }
}

您还可以使用新的switch-case语法并通过使用enum s 进行各种选择来进一步优化。

Answer 2

您正在将整个数组与单个字符串进行比较。 使用 choices[0].equals("Area")。 现在，这会将选择数组与索引 0 处的字符串与区域进行比较。