！技术java 进行数据库查询，while (resultSet.next()) 直接为false，不执行，为啥

 
 import java.sql.*; 
  
 public class Student_mysql { 
 	private Connection connection; 
 	private Statement statement; 
 	public boolean getStudent_welcome(String sql, String str1, String str2) ////传入sql语句字符串 
 			throws SQLException, ClassNotFoundException { 
 		try { 
 			Class.forName("com.mysql.jdbc.Driver"); 
 			System.out.println("Success loading Mysql Driver!"); 
 		} catch (Exception e) { 
 			System.out.println("Error loading Mysql Driver!"); 
 			e.printStackTrace(); 
 		} 
 		String url = "jdbc:mysql://localhost:3306/myschool"; 
 		String username = "root"; 
 		String password = "123"; 
 		connection = DriverManager.getConnection(url, username, password);  
 		System.out.println("Success connect!"); 
 		System.out.println(sql); 
 		statement = connection.createStatement(); 
 		ResultSet resultSet = statement.executeQuery(sql); 
 		while (resultSet.next()) {   //不执行，直接跳过到connection.close();return false;了，为啥？ 
  
 			System.out.println(str1); 
 			try { 
 				if (str1 == resultSet.getString(1) 
 						&& str2 == resultSet.getString(2)){ 
 					connection.close(); 
 					return true; 
 				} 
 				else 
 					connection.close(); 
 					return false; 
 			} catch (Exception e) { 
 				e.printStackTrace(); 
 				connection.close(); 
 				return false; 
 			} 
 		} 
 		connection.close(); 
 		return false; 
 	} 
 }