java - 在函数中使用泛型的问题

Question

我有这个功能，需要把它变成一个功能。唯一的区别是输入变量 sourceColumnValue 的类型。此变量可以是 String 或 Integer 但函数的返回值必须始终是 Integer。 我知道我需要使用泛型但做不到。

    public Integer selectReturnInt(String tableName, String sourceColumnName, String sourceColumnValue, String targetColumnName) {
    Integer returned = null;
    String query = "SELECT "+targetColumnName+" FROM "+tableName+" WHERE "+sourceColumnName+"='"+sourceColumnValue+"' LIMIT 1";

    try {
        Connection connection = ConnectionManager.getInstance().open();
        java.sql.Statement statement = connection.createStatement();
        statement.execute(query.toString());
        ResultSet rs = statement.getResultSet();
        while(rs.next()){
            returned = rs.getInt(targetColumnName);
        }

        rs.close();
        statement.close();
        ConnectionManager.getInstance().close(connection);
    } catch (SQLException e) {
        System.out.println("Заявката не може да бъде изпълнена!");
        System.out.println(e);
    }

    return returned;
}


// SELECT (RETURN INTEGER)
public Integer selectIntReturnInt(String tableName, String sourceColumnName, Integer sourceColumnValue, String targetColumnName) {
    Integer returned = null;
    String query = "SELECT "+targetColumnName+" FROM "+tableName+" WHERE "+sourceColumnName+"='"+sourceColumnValue+"' LIMIT 1";

    try {
        Connection connection = ConnectionManager.getInstance().open();
        java.sql.Statement statement = connection.createStatement();
        statement.execute(query.toString());
        ResultSet rs = statement.getResultSet();
        while(rs.next()){
            returned = rs.getInt(targetColumnName);
        }

        rs.close();
        statement.close();
        ConnectionManager.getInstance().close(connection);
    } catch (SQLException e) {
        System.out.println("Заявката не може да бъде изпълнена!");
        System.out.println(e);
    }

    return returned;
}

Answer 1

不您不需要为此使用泛型。当您支持的类型可能很多并且您事先不知道它们并且它们共享一些共同点时，应该使用泛型在他们中。

仅针对两种类型泛型不是一个好的选择。使用 objects 可能是更好的选择。

也许我会说您甚至不需要合并这些函数，这就是多态性的用途。保持谨慎将使代码更具可读性