我试图使用一个方法，这是在不同的类，但它产生一个错误

Question

这是我想使用insertData()方法的主要类。这个方法来自不同的类InsertOperation，两个类都在同一个包中，但我仍然不能使用该方法。我是java的新手，我还在努力掌握它。

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();
}
}
}  
}

下面是InsertOperation类的代码:

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");
}     
}
}

错误如下:

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

Answer 1

如果要访问instance方法，需要创建一个实例。

InsertOperation iop = new InsertOperation();

我想你可能忘记这里的新关键词了。

否则，在声明insertData()方法时可以使用静态关键字，如下所示。

public static void insertData() throws SQLException

然后调用方法名访问那个方法

Ex: insertData();

Answer 2

缺失"new"创建对象的关键字。

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

应该

InsertOperation iop = new InsertOperation();