How to solve the problem of database content output

Why code one can run , Code two doesn't work

 Code 1 javaimport java.sql.Connection;import java.sql.DriverManager;//import java.sql.Statement;import java.util.ArrayList;import com.mysql.jdbc.Statement;import java.sql.ResultSet;//import java.sql.SQLException;/** * * @author * */public class sql {    ArrayList<Book>  tushu=new ArrayList<>();     ArrayList<CD>  b=new ArrayList<>();     ArrayList<Picture>  c=new ArrayList<>();        Connection con=null;        Statement st=null;    public static void main(String[] args) throws Exception  {        // TODO Auto-generated method stub        ResultSet rs=null;        java.sql.Statement st=null;        Connection con=null;        Class.forName("com.mysql.jdbc.Driver");        con=DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/chengxusheji?useSSL=false","root","03579631");        st= con.createStatement();        String sql="select * from a";        rs=st.executeQuery(sql);        while(rs.next()) {             System.out.print(rs.getString(1)+"\t");             System.out.print(rs.getString(2)+"\t");             System.out.print(rs.getString(3)+"\t");             System.out.print(rs.getString(4)+"\t");             System.out.print(rs.getString(5)+"\t");             System.out.print(rs.getString(6)+"\t");             System.out.print(rs.getInt(7)+"\t");             System.out.print("\n");         }    }} Code 2 java    import java.util.ArrayList;import java.util.Scanner;import java.sql.*;import java.sql.Connection;import java.sql.DriverManager;//import java.sql.Statement;import com.mysql.jdbc.Statement;import java.sql.ResultSet;public class KSone {    Scanner ad=new Scanner(System.in);    ArrayList<Book>  a=new ArrayList<>();     ArrayList<CD>  b=new ArrayList<>();     ArrayList<Picture>  c=new ArrayList<>();     /* * */     PreparedStatement  ps1=null;     PreparedStatement  ps2=null;     PreparedStatement  ps3=null;     String sql="insert into a values(?,?,?,?,?,?,?)";     String sql2="insert into b values(?,?,?,?,?,?,?)";     String sql3="insert into c values(?,?,?,?,?,?,?)";         /* * */    public static void main(String[] args) throws Exception {        // TODO Auto-generated method stub        Scanner ad=new Scanner(System.in);        KSone p=new KSone();        /* *  Database definition  */         Class.forName("com.mysql.jdbc.Driver");         Connection con=null;         PreparedStatement  ps1=null;         PreparedStatement  ps2=null;         PreparedStatement  ps3=null;         con=DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/chengxusheji?useSSL=false","root","03579631");         String sql="insert into a values(?,?,?,?,?,?,?)";         String sql2="insert into b values(?,?,?,?,?,?,?)";         String sql3="insert into c values(?,?,?,?,?,?,?)";             ps1=con.prepareStatement(sql);         ps2=con.prepareStatement(sql2);         ps3=con.prepareStatement(sql3);        /* * */         while(true) {         System.out.println("*********** Media library management system *************");        System.out.println("\t1. Add items ");        System.out.println("\t2. Query items ");        System.out.println("\t3. Show inventory ");        System.out.println("\t4. Edit item ");        System.out.println("\t5. Delete items ");        System.out.println("\t6. Statistics ");        System.out.println("\t7. Storage of items ");        System.out.println("\t8. Read items ");        System.out.println("**********************************");            int s=ad.nextInt();        switch (s) {        case 1:            p.function1();            break;        case 2:            p.function2();            break;        case 3:            p.function3();            break;        case 4:            p.function4();            break;        case 5:            p.function5();            break;        case 6:            p.function6();            break;        case 7:            p.function7();            break;        }    }    }//........public void function8() throws Exception {      //       ResultSet rs=null;        java.sql.Statement st=null;        Connection con=null;        Class.forName("com.mysql.jdbc.Driver");        con=DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/chengxusheji?useSSL=false","root","03579631");        st= con.createStatement();        String sql="select * from a";        rs=st.executeQuery(sql);        //        ResultSet rs2=null;        java.sql.Statement st2=null;        st2= con.createStatement();        String sql2="select * from b";        rs2=st2.executeQuery(sql2);        //        ResultSet rs3=null;        java.sql.Statement st3=null;        st3= con.createStatement();        String sql3="select * from c";        rs3=st3.executeQuery(sql3);        //        while(rs.next()) {             System.out.print(rs.getString(1)+"\t");             System.out.print(rs.getString(2)+"\t");             System.out.print(rs.getString(3)+"\t");             System.out.print(rs.getString(4)+"\t");             System.out.print(rs.getString(5)+"\t");             System.out.print(rs.getString(6)+"\t");             System.out.print(rs.getInt(7)+"\t");             System.out.print("\n");         }         if (rs != null) {             rs.close();         }         if (st != null) {         st.close();         }        //        while(rs2.next()) {             System.out.print(rs2.getString(1)+"\t");             System.out.print(rs2.getString(2)+"\t");             System.out.print(rs2.getString(3)+"\t");             System.out.print(rs2.getString(4)+"\t");             System.out.print(rs2.getString(5)+"\t");             System.out.print(rs2.getString(6)+"\t");             System.out.print(rs2.getString(7)+"\t");             System.out.print("\n");         }         if (rs2 != null) {             rs2.close();         }         if (st2 != null) {         st2.close();         }        //        while(rs3.next()) {             System.out.print(rs3.getString(1)+"\t");             System.out.print(rs3.getString(2)+"\t");             System.out.print(rs3.getString(3)+"\t");             System.out.print(rs3.getString(4)+"\t");             System.out.print(rs3.getString(5)+"\t");             System.out.print(rs3.getInt(6)+"\t");             System.out.print(rs3.getInt(7)+"\t");             System.out.print("\n");         }         if (rs3 != null) {             rs3.close();         }         if (st3 != null) {         st3.close();         }         if (con != null) {         con.close();         }}

Operation results and error reporting contents

My solution ideas and tried methods

What I want to achieve