Io 异常: The Network Adapter could not establish the connection 求高手解答，万分感谢~

import java.sql.*;

public class sql {

public static void main(String[] args) throws SQLException, InstantiationException, IllegalAccessException {
String s1 = null;
String s2 = null;
String s3 = null;
try {
Class.forName ("oracle.jdbc.driver.OracleDriver");
} catch (ClassNotFoundException e) {
e.printStackTrace();
System.exit(0);
}
System.out.println("数据库连接中。。。");
Connection conn = DriverManager.getConnection
("jdbc:oracle:thin:@localhost:1521:ORCL", "scott", "tiger");
System.out.println("连接成功！~");
String sql = "SELECt * FROM Students WHERe name = ?";
PreparedStatement pStm = conn.prepareStatement(sql);
pStm.setString(1, "张三");
ResultSet result = pStm.executeQuery();
while(result.next()){
s1 = result.getString("name");
s2 = result.getString("id");
s3 = result.getString("grade");
}

System.out.println(s1);
System.out.println(s2);
System.out.println(s3);
result.close();
pStm.close();
conn.close();
}

}
oracle的2个服务都开了，用sqlplus连接数据库没问题也能建表插入数据。不知道是不是要设置什么数据源的问题？有高手知道吗？
提示信息：
数据库连接中。。。
Exception in thread "main" java.sql.SQLException: Io 异常: The Network Adapter could not establish the connection
at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:112)
at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:146)
at oracle.jdbc.driver.DatabaseError.throwSqlException(DatabaseError.java:255)
at oracle.jdbc.driver.T4CConnection.logon(T4CConnection.java:387)
at oracle.jdbc.driver.PhysicalConnection.<init>(PhysicalConnection.java:414)
at oracle.jdbc.driver.T4CConnection.<init>(T4CConnection.java:165)
at oracle.jdbc.driver.T4CDriverExtension.getConnection(T4CDriverExtension.java:35)
at oracle.jdbc.driver.OracleDriver.connect(OracleDriver.java:801)
at java.sql.DriverManager.getConnection(Unknown Source)
at java.sql.DriverManager.getConnection(Unknown Source)
at sql.main(sql.java:16)

("jdbc:oracle:thin:@localhost:1521:ORCL", "scott", "tiger"); 这行出错了，你看看你数据库实例 用户名 密码 写错了没

和防火墙没关系 检查：Connection 顺便检查localhost:1521:ORCL