如下，为什么它无论是“==”还是“.equals()”都先试试不相等的！求解决！

Question

import javax.swing.*;import java.awt.*;import java.sql.*;import java.awt.event.*;import java.sql.Connection;import java.sql.DriverManager;import java.sql.SQLException;public class JFrameDemo{String passwordD=null;public static String persontyDD=null;public JFrameDemo(){final JFrame frame1 = new JFrame("超市管理系统登陆界面");final JButton button = new JButton("登陆");JLabel labelName = new JLabel("请输入账号");JLabel labelNumber = new JLabel("请输入密码");final JTextField tfName = new JTextField(12);final JTextField tfNumber = new JTextField(12);JMenuBar menubar = new JMenuBar();JMenu mu = new JMenu("功能");JMenuItem help = new JMenuItem("帮助");JMenuItem quet = new JMenuItem("退出");button.addActionListener(new ActionListener() {public void actionPerformed(ActionEvent e) {Connection con;Statement sql;ResultSet rs = null;String fu="超级用户";if(e.getSource()==button){String idin = tfName.getText();String keyin = tfNumber.getText();try {Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver");String url="jdbc:sqlserver://localhost:1433;databaseName=Supermarket";String user="sa";String password="123456";con=DriverManager.getConnection(url,user,password);sql = con.createStatement();rs = sql.executeQuery("SELECT * FROM password where ID='"+ idin + "'");while (rs.next()) {passwordD= rs.getString(2); persontyDD= rs.getString(3);}con.close();} catch (Exception g){System.out.println(g);}if (persontyDD!=null){frame1.dispose();ViewDemo frame=new ViewDemo();System.out.println(persontyDD);if(persontyDD==fu){System.out.println("1");}}}else{frame1.dispose();Close frame=new Close();}}} );public static void main(String args[]) {new JFrameDemo();}}

Answer 1

1、字符串判断内容相等用.equals();如果是比较是否是同一个对象（即内容和引用相同），则用==
2、passwordD= rs.getString(2); 改为：passwordD= rs.getString("passwordD");
persontyDD= rs.getString(3);改为：persontyDD= rs.getString("persontyDD");
因为你的数据库中字段的顺序和你getString后面的数字不一致。
写了个小程序，你看看。

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class LCP_TEST extends Test{
public static void main(java.lang.String[] args) {
String url = "jdbc:oracle:thin:@100.100.100.129:1521:auxoms";
String user = "osm";
String password = "osm";
try {
Class.forName("oracle.jdbc.OracleDriver");
Connection conn = DriverManager.getConnection(url, user, password);
Statement stmt = conn.createStatement();
String sql = " select 'aa' username,'123456' passwordD from dual";
ResultSet rs = stmt.executeQuery(sql);
while (rs.next()) {
String username = rs.getString("username");
String passwordD = rs.getString("passwordD");
System.out.println("username:"+username);
System.out.println("passwordD:"+passwordD);
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
}
}
}

Answer 2

“==”肯定是不行的，因为两个字符串的地址可能不相同，应该用.equals()，不知是否是您写的有问题，其实更简单的是不用单独赋值一个fu，直接.equals("超级用户")就行了，你先试试。

Answer 3

看看你查询出来的结果里面是不是包含空格？删除字符串首部和尾部的空格,用.equals().Trim ( string ) 试试 !