Question

我是Java的新手，无法理解try / catch在以下代码中的位置。这个项目还有很多，但这是问题领域

Statement stmt = con.createStatement();
    String query = "SELECT FirstName, LastName FROM Customer";
    ResultSet rs = stmt.executeQuery(query);
    while (rs.next())
    {
        String ln = rs.getString("FirstName");
        String ln1 = rs.getString("LastName");
        System.out.println(ln + " " + ln1);
    }

Answer 1

如果您使用的是Java 7+，则可以使用try-with-resources。

文档链接中的一个示例：

public static void viewTable(Connection con) throws SQLException {

    String query = "select COF_NAME, SUP_ID, PRICE, SALES, TOTAL from COFFEES";

    try (Statement stmt = con.createStatement()) {
        ResultSet rs = stmt.executeQuery(query);

        while (rs.next()) {
            String coffeeName = rs.getString("COF_NAME");
            int supplierID = rs.getInt("SUP_ID");
            float price = rs.getFloat("PRICE");
            int sales = rs.getInt("SALES");
            int total = rs.getInt("TOTAL");

            System.out.println(coffeeName + ", " + supplierID + ", " + 
                           price + ", " + sales + ", " + total);
        }
    } catch (SQLException e) {
        JDBCTutorialUtilities.printSQLException(e);
    }
}

Answer 2

只要调用可以抛出异常的方法，就会使用Try-catch。在你的情况下：

ResultSet rs = null;    
 try {
Statement stmt = con.createStatement();
String query = "SELECT FirstName, LastName FROM Customer";
  rs = stmt.executeQuery(query);
catch(Exception e){
  e.printStackTrace();
}

例如

。

Answer 3

可以在ResultSet的文档中找到try / catch的需要。我假设executeQuery在输入SQL查询中抛出了语法错误的异常。不确定，但getString也可能抛出异常。

如果executeQuery需要一个......

@echo off
setlocal enabledelayedexpansion
set count=0
for /f %%D in ('wmic volume get DriveLetter^, Label ^| find /i "Video"') do ( 
  set /a count+=1
  set drive!count!=%%D
)
echo %count% drives found:
set drive 2>nul
if %count% gtr 4 echo too much...

在java代码中插入try / catch的位置

3 个答案: