我制作了一个简单的科学测验java应用程序，包含4个框架：登录，菜单，测试和结果。
前三帧工作正常但是当我点击显示结果时它显示错误。 这是我在Result JFrame中的代码。如果你想我也可以发送Test JFrame的编码。
这是我的错误
java.sql.SQLException：对空结果集的非法操作。 在com.mysql.jdbc.SQLError.createSQLException（SQLError.java:1055） 在com.mysql.jdbc.SQLError.createSQLException（SQLError.java:956） 在com.mysql.jdbc.SQLError.createSQLException（SQLError.java:926） 在com.mysql.jdbc.ResultSetImpl.checkRowPos（ResultSetImpl.java:815） 在com.mysql.jdbc.ResultSetImpl.getStringInternal（ResultSetImpl.java:5528） 在com.mysql.jdbc.ResultSetImpl.getString（ResultSetImpl.java:5448） 在com.mysql.jdbc.ResultSetImpl.getFloat（ResultSetImpl.java:2499） 在Test.ResultBTNActionPerformed（Test.java:292） 在Test.access $ 500（Test.java:18） 在Test $ 6.actionPerformed（Test.java:215） 在javax.swing.AbstractButton.fireActionPerformed（AbstractButton.java:1995） 在javax.swing.AbstractButton $ Handler.actionPerformed（AbstractButton.java:2318） 在javax.swing.DefaultButtonModel.fireActionPerformed（DefaultButtonModel.java:387） 在javax.swing.DefaultButtonModel.setPressed（DefaultButtonModel.java:242） 在javax.swing.plaf.basic.BasicButtonListener.mouseReleased（BasicButtonListener.java:236） at java.awt.Component.processMouseEvent（Component.java:6216） 在javax.swing.JComponent.processMouseEvent（JComponent.java:3265） 在java.awt.Component.processEvent（Component.java:5981） at java.awt.Container.processEvent（Container.java:2041） at java.awt.Component.dispatchEventImpl（Component.java:4583） at java.awt.Container.dispatchEventImpl（Container.java:2099） at java.awt.Component.dispatchEvent（Component.java:4413） at java.awt.LightweightDispatcher.retargetMouseEvent（Container.java:4556） at java.awt.LightweightDispatcher.processMouseEvent（Container.java:4220） at java.awt.LightweightDispatcher.dispatchEvent（Container.java:4150） at java.awt.Container.dispatchEventImpl（Container.java:2085） at java.awt.Window.dispatchEventImpl（Window.java:2475） at java.awt.Component.dispatchEvent（Component.java:4413） at java.awt.EventQueue.dispatchEvent（EventQueue.java:599） at java.awt.EventDispatchThread.pumpOneEventForFilters（EventDispatchThread.java:269） at java.awt.EventDispatchThread.pumpEventsForFilter（EventDispatchThread.java:184） at java.awt.EventDispatchThread.pumpEventsForHierarchy（EventDispatchThread.java:174） at java.awt.EventDispatchThread.pumpEvents（EventDispatchThread.java:169） at java.awt.EventDispatchThread.pumpEvents（EventDispatchThread.java:161） 在java.awt.EventDispatchThread.run（EventDispatchThread.java:122）
import java.sql.*;
import javax.swing.table.*;
import javax.swing.JOptionPane;
public class Result extends javax.swing.JFrame {
float result;
String ID;
/** Creates new form Result */
public Result() {
initComponents();
}
public Result(float res, String id)
{
initComponents();
result = res;
ID = id;
Score.setText(res + "%");
try {
Class.forName("java.sql.Driver");
String database = "jdbc:mysql://localhost:3306/quizdb";
Connection conn = DriverManager.getConnection(database, "root", "1234");
Statement stmt = conn.createStatement();
String sql = "select * from Result where ID = '" + ID + "'";
ResultSet rs = stmt.executeQuery(sql);
Object[] newrow = new Object[5];
newrow[0] = "MAX MARKS";
rs.next();
for(int i=1; i<=4;i++)
newrow = rs.getString(i+1);
DefaultTableModel tm = (DefaultTableModel)scoreTBL.getModel();
tm.addRow(newrow);
}
catch (Exception e) { JOptionPane.showMessageDialog(null,"" + e);
}
}
testJFrame的编码
import java.sql.*;
import javax.swing.JOptionPane;
public class Test extends javax.swing.JFrame {
String ID;
String Subject;
int index =1;
int max =0;
int result = 0;
char [] answers;
/** Creates new form Test */
public Test()
{
initComponents();
}
public Test(String subject, String id)
{
initComponents();
ID = id;
Subject = subject;
PrevBTN.setVisible(false);
try
{
Class.forName("java.sql.Driver");
String database = "jdbc:mysql://localhost:3306/quizdb";
Connection conn = DriverManager.getConnection(database, "root", "1234");
Statement stmt = conn.createStatement();
String sql = "select max(SNo) from " + Subject;
ResultSet rs = stmt.executeQuery(sql);
rs.next();
max = rs.getInt(1);
answers = new char[max];
for(int i=0; i<max;i++)
answers[i] = 'e';
rs.close();
stmt.close();
conn.close();
getQues();
}
catch(Exception e){ JOptionPane.showMessageDialog(null,""+ e);
}
}
private void getQues()
{
try
{
/* Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
String database ="jdbc:odbc:Driver={Microsoft Access Driver (*.mdb)};DBQ=ELearning.mdb;";
Connection conn = DriverManager.getConnection(database, "", "");
Statement stmt = conn.createStatement(); */
Class.forName("java.sql.Driver");
String database = "jdbc:mysql://localhost:3306/quizdb";
Connection conn = DriverManager.getConnection(database, "root", "1234");
Statement stmt = conn.createStatement();
String sql = "select * from " + Subject + " where SNo = " + index;
ResultSet rs = stmt.executeQuery(sql);
rs.next();
QuesTA.setText("\nQ" + index + ". " + rs.getString(2));
a.setText(rs.getString("a"));
b.setText(rs.getString("b"));
c.setText(rs.getString("c"));
d.setText(rs.getString("d"));
a.setSelected(answers[index-1] == 'a');
b.setSelected(answers[index-1] == 'b');
c.setSelected(answers[index-1] == 'c');
d.setSelected(answers[index-1] == 'd');
e.setSelected(answers[index-1] == 'e');
rs.close();
stmt.close();
conn.close();
}
catch(Exception e){ JOptionPane.showMessageDialog(null,""+ e); }
}
private void PrevBTNActionPerformed(java.awt.event.ActionEvent evt) {
index--;
getQues();
if(index == 1)
PrevBTN.setVisible(false);
if(index < max)
NextBTN.setVisible(true);
}
private void NextBTNActionPerformed(java.awt.event.ActionEvent evt) {
index++;
getQues();
if(index == max)
NextBTN.setVisible(false);
if(index > 1)
PrevBTN.setVisible(true);
}
private void bActionPerformed(java.awt.event.ActionEvent evt) {
answers[index-1] = 'b';
}
private void ResultBTNActionPerformed(java.awt.event.ActionEvent evt) {
try
{
/* Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
String database ="jdbc:odbc:Driver={Microsoft Access Driver (*.mdb)};DBQ=ELearning.mdb;";
Connection conn = DriverManager.getConnection(database, "", "");
Statement stmt = conn.createStatement(); */
Class.forName("java.sql.Driver");
String database = "jdbc:mysql://localhost:3306/quizdb";
Connection conn = DriverManager.getConnection(database, "root", "1234");
Statement stmt = conn.createStatement();
String sql = "select Result from " + Subject;
ResultSet rs = stmt.executeQuery(sql);
int i = 0;
while(rs.next())
{
char ans = rs.getString(1).charAt(0);
if(ans == answers[i])
result++;
i++;
}
float res = ((float)result * 100 ) / max;
sql = "Select " + Subject + "Result from Result where ID = '" + ID + "'";
rs = stmt.executeQuery(sql);
rs.next();
if(res > rs.getFloat(1))
{
sql = "update Result set " + Subject + "Result = " + res + " where ID = '" + ID + "'";
stmt.executeUpdate(sql);
}
stmt.close();
conn.close();
new Result(res,ID).setVisible(true);
this.setVisible(false);
}
catch(Exception e){ JOptionPane.showMessageDialog(null,""+ e); }
}
private void aActionPerformed(java.awt.event.ActionEvent evt) {
answers[index-1] = 'a';
}
private void cActionPerformed(java.awt.event.ActionEvent evt) {
answers[index-1] = 'c';
}
private void dActionPerformed(java.awt.event.ActionEvent evt) {
answers[index-1] = 'd';
}
/**
* @param args the command line arguments
*/
public static void main(String args[]) {
java.awt.EventQueue.invokeLater(new Runnable() {
public void run() {
new Test().setVisible(true);
}
});
}
答案 0 :(得分：-1)
更改此代码
rs.next();
for(int i=1; i<=4;i++)
newrow = rs.getString(i+1);
DefaultTableModel tm = (DefaultTableModel)scoreTBL.getModel();
tm.addRow(newrow);
到
DefaultTableModel tm = (DefaultTableModel)scoreTBL.getModel();
while(rs.next())
{
java.util.Vector row = new java.util.Vector();
for(int i=1; i<=4;i++)
{
row.add(rs.getString(i));
}
tm.addRow(row);
}
修改
在您编写的代码中
rs.next();
max = rs.getInt(1);
将其更改为
if(rs.next())
max = rs.getInt(1);
如果上述条件为真，那么只评估下一个语句。