问题

import java.util.Scanner;

public class Example {
    static String[] cat = new String[5];  // Moved cat array to a higher scope
    
    public static void main(String args[]) {
        Scanner in = new Scanner(System.in);
        
        cat[0] = "Design";
        cat[1] = "Biology";
        cat[2] = "Business";
        cat[3] = "Health";
        cat[4] = "History";

        System.out.print("Enter Category: ");
        String e = in.nextLine();
        int index = new Example().Find(e);  // Pass the entered category to the Find method
        if (index != -1) {
            System.out.print("The index of " + e + " is: " + index);
        } else {
            System.out.print("Not found");
        }
    }

    public int Find(String e) {
        int index = -1;
        for (int i = 0 ; i < cat.length; i++) {
            if (cat[i].equals(e)) {
                index = i;
                break;  // Exit the loop once the category is found
            }
        }
        return index;  // Return the index after the loop completes
    }
}

import java.util.Scanner;
public class Example {
    public static void main(String args[]) {
        Scanner in = new Scanner(System.in);
        String[] cat = new String[5];
        cat[0] = "Design";
        cat[1] = "Biology";
        cat[2] = "Business";
        cat[3] = "Health";
        cat[4] = "History";

        System.out.print("Enter Category: ");
        String e = in.nextLine();
        new Example().Find();
        System.out.print("The index of " + cat[i] + " is: " + index);
    }

    public int Find() {
        int index = -1;
        for (int i = 0 ; i < cat.length; i++) {
            if (cat[i].equals(e)) {
                index = i;
                return index;
            }
        }
    }
}

答案1

得分: 0

注意到了一些问题。看起来你需要了解一下作用域 https://www.geeksforgeeks.org/variable-scope-in-java/ ：

1. 需要将 e 传递给 Find 方法，因为你在主函数中声明了它的局部变量。
2. 需要在主函数中设置 index 变量。
3. 你返回的索引是从 0 开始的，所以不确定你是否希望是这样。我的答案假设你不希望是从 0 开始的。
4. 需要将 cat 数组传递给方法。

```java
import java.util.Scanner;

public class Example {
    public static void main(String args[]) {
        Scanner in = new Scanner(System.in);
        String[] cat = new String[5];
        cat[0] = "Design";
        cat[1] = "Biology";
        cat[2] = "Business";
        cat[3] = "Health";
        cat[4] = "History";

        System.out.print("Enter Category: ");
        String e = in.nextLine();
        int index = Find(e, cat);
        System.out.print("The index of " + e + " is: " + index);
    }

    public static int Find(String e, String[] cat) {
        for (int i = 0; i < cat.length; i++) {
            if (cat[i].equals(e)) {
                return i + 1;
            }
        }
        return -1;
    }
}

<details>
<summary>英文:</summary>

Noticed a few thing. Looks like you need to read up on scope https://www.geeksforgeeks.org/variable-scope-in-java/:

1. Need to pass in e to find since you have it local to main
2. Need to set index variable in main.
3. Index you are returning is 0 based so not sure if you want that. My answer assumes you don&#39;t.
4. Need to pass in cat array

import java.util.Scanner;

public class Example {
public static void main(String args[]) {
Scanner in = new Scanner(System.in);
String[] cat = new String[5];
cat[0] = "Design";
cat[1] = "Biology";
cat[2] = "Business";
cat[3] = "Health";
cat[4] = "History";

    System.out.print("Enter Category: ");
    String e = in.nextLine();
    int index = Find(e);
    System.out.print("The index of " + cat[i] + " is: " + index);
}

public int Find(String e, String [] cat) {
    int index = -1;
    for (int i = 0 ; i < cat.length; i++) {
        if (cat[i].equals(e)) {
            return i+1;
        }
    }
}

}

</details>



# 答案2
**得分**: 0

你很接近了。以下是一种带有注释解释的方法来完成这个任务。

```java
    Scanner in = new Scanner(System.in);

    // 你初始化数组的方式是可以的，但是也可以使用下面这种更简单的方式。
    // String[] cat =  { "Design", "Biology", "Business", "Health", "History" };

    String[] cat = new String[5];
    cat[0] = "Design";
    cat[1] = "Biology";
    cat[2] = "Business";
    cat[3] = "Health";
    cat[4] = "History";

    System.out.print("输入类别：");
    String e = in.nextLine();

需要将类别字符串和数组传递给 `find` 方法。该方法将返回字符串在数组中的索引。

```java
    int index = new Example().find(e, cat);

现在验证索引是否有效。-1 表示未找到。其他任何值都应该提供在数组中的位置。

    if (index < 0) {
        System.out.println(e + " 未找到！");
    }
    else {

现在使用索引打印出对应的值。

        System.out.print(cat[index] + " 的索引是：" + index);
    }

这个方法几乎正确，只需要将字符串和数组传递给 `find` 方法。并且返回 `i` 对于索引已经足够了。按照约定，方法名应该以小写字母开头。

```java
public int find(String str, String[] arr) {
    for (int i = 0; i < arr.length; i++) {
        if (arr[i].equals(str)) {
            return i;
        }
    }
    return -1;
}

Scanner in = new Scanner(System.in);

// The way you initialzied your array is fine but you 
// could do the same thing like this which most times is easier.

// String[] cat =  { "Design", "Biology", "Business", "Health", "History" };

String[] cat = new String[5];
cat[0] = "Design";
cat[1] = "Biology";
cat[2] = "Business";
cat[3] = "Health";
cat[4] = "History";

System.out.print("Enter Category: ");
String e = in.nextLine();

int index = new Example().find(e, cat);

if (index < 0) {
    System.out.println(e + " not found!");
}
else {

    System.out.print("The index of " + cat[index] + " is: " + index);
}

public int find(String str, String[] arr) {
    for (int i = 0; i < arr.length; i++) {
        if (arr[i].equals(str)) {
           return i;
        }
    }
    return -1;
}