我正在尝试使用不同 class 中的方法，但它会产生错误

Question

这里是主要的 class，我想在其中使用 insertData() 方法。此方法来自不同的 class InsertOperation，两个 class 都在同一个包中，但我仍然无法使用该方法。我是 java 的新手，我仍在努力掌握这一切。

package crudoperations;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.sql.*;

public class CRUDOperations {
    /*
    private static final String CREATE_TABLE = "CREATE TABLE employee "
                                    + "(" + "user_id INT(100) NOT NULL PRIMARY KEY," + 
                                        "first_name VARCHAR(100)," +
                                        "last_name VARCHAR(100)," +
                                        "contact_number INT(10)," +
                                        "email_id VARCHAR(100))";
*/
    public static void main(String[] args) throws SQLException {
        Connection con = null;
        PreparedStatement stmt = nulll;
        try{
            con = // File enter code here Connection.getConnection();
            InsertOperation iop = InsertOperation(); //Showing error in this line
            iop.insertData();
            
            //System.out.println("Connected");
            //stmt = con.prepareStatement(CREATE_TABLE);
            //stmt.executeUpdate();
            
            //System.out.println("Table Created");
            
        }
        catch(SQLException e){
            System.err.print(e);
        }
        finally{
            if(con != null){
                con.close();
            }
        }
    }  
}

这是 InsertOperation 的代码 class:

package crudoperations;

import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;
import java.util.Scanner;

public class InsertOperation {
    public void insertData() throws SQLException {
        Scanner sc = new Scanner(System.in);
        
        System.out.println("Enter the First Name: ");
        String user_firstname = sc.next();
        
        System.out.println("Enter the Last Name: ");
        String user_lastname = sc.next();
        
        System.out.println("Enter the Contact Number: ");
        String user_contact = sc.next();
        
        System.out.println("Enter the Email ID: ");
        String user_email = sc.next();
        
        Connection con = null;
        con = FileConnection.getConnection();
        PreparedStatement pst = con.prepareStatement(
                "INSERT INTO employees "
             + " (user_id, first_name, last_name, contact_number, email_id)"
             + " VALUES (?,?,?,?)");
        
        pst.setString(2, user_firstname);
        pst.setString(3, user_lastname);
        pst.setString(4, user_contact);
        pst.setString(5, user_email);
        
        int i = pst.executeUpdate();
        if(i != 0){
            System.out.print("success");       
        }
        else{
            System.out.print("error");
        }     
    }
}

这是错误：

error: cannot find symbol
            InsertOperation iop = InsertOperation();
  symbol:   method InsertOperation()
  location: class CRUDOperations

Answer 1

对象创建缺少“new”关键字。

```
   InsertOperation iop = InsertOperation(); //Showing error in this line
```

应该是

InsertOperation iop = new InsertOperation();

Answer 2

要访问实例方法需要创建实例

InsertOperation iop = new InsertOperation();

我想你可能忘记了这里的新关键词。

否则，您可以在如下声明 insertData() 方法时使用静态关键字。

public static void insertData() throws SQLException

然后访问只调用方法名称的方法。

Ex: insertData();

我正在尝试使用不同 class 中的方法，但它会产生错误

I am trying to use a method which is in different class but it generates an error

java

jdbc