在java中循环之外访问字符串变量? [英] Access string variable outside for loop in java?

问题描述

大家好，我想在循环外访问一个字符串变量，以便我可以将其用于进一步的编码.在这里，我试图从Jtable中获取值并将其存储在字符串中，以创建数据库表.整个代码在这里: http://textuploader.com/?p=6&id=zVEWY

Coding :
int row = table.getRowCount();

int column = table.getColumnCount();

for (int j = 0; j < row; j++) {

for (int i = 0; i < column; i++) {

 //System.out.println(table.getValueAt(j, i));
  String readstr = (String) table.getValueAt(j, i);   // I WANT TO ACCESS THIS STRING


 }

 }


 try{
   // FILE READ AND TABLE CREATE
   String tname="example";
   String dbname="DB123";
    Class.forName("com.mysql.jdbc.Driver");
    Connection conn= (Connection)    DriverManager.getConnection("jdbc:mysql://localhost:3306/DB123","root","");
    Statement stmt=(Statement) conn.createStatement();

    System.out.println("connect");



     DatabaseMetaData dmd = (DatabaseMetaData) conn.getMetaData();
     while((readstr=brr.readLine())!=null)                     // TO USE IT HERE
    {
     ResultSet rs = dmd.getTables(null,"MigrationDB", "example", null);
     //set not null column
     if (String.valueOf(readstr).contains("NO"))
  readstr=readstr.replaceAll("NO", "not null");
     else if(String.valueOf(readstr).contains("YES"))
       readstr=readstr.replaceAll("YES", "");
     if(String.valueOf(readstr).contains("PRIMARY"))
         readstr=readstr.replaceFirst("PRIMARY","primary key");
    System.out.println("replace string "+readstr);
  int k=1;
   if (!rs.next())
  {
  stmt.executeUpdate("CREATE TABLE "+tname+ "("+readstr+")");

    }
 else{
     System.out.println(readstr);
     stmt.executeUpdate("ALTER TABLE "+tname+ " ADD("+readstr+")");
      System.out.println("altered");

      }
     }

    }
     catch (Exception e){}

   }


    }

谢谢.

解决方案

您需要了解什么是局部变量，以及它们的生存期是多少.我建议您通读本教程: http://www.tutorialspoint.com/java/java_variable_types.htm

在这种情况下，只需要在for循环外声明readstr即可.

String readstr;
for(//loop condition) {
readstr = read value ;
}

hi folks i want to access a string variable outside for loop, so that i can use it for further coding. Here i am trying to get the values from Jtable and store it in string, to create a database table. The Whole Code is here: http://textuploader.com/?p=6&id=zVEWY

Coding :
int row = table.getRowCount();

int column = table.getColumnCount();

for (int j = 0; j < row; j++) {

for (int i = 0; i < column; i++) {

 //System.out.println(table.getValueAt(j, i));
  String readstr = (String) table.getValueAt(j, i);   // I WANT TO ACCESS THIS STRING


 }

 }


 try{
   // FILE READ AND TABLE CREATE
   String tname="example";
   String dbname="DB123";
    Class.forName("com.mysql.jdbc.Driver");
    Connection conn= (Connection)    DriverManager.getConnection("jdbc:mysql://localhost:3306/DB123","root","");
    Statement stmt=(Statement) conn.createStatement();

    System.out.println("connect");



     DatabaseMetaData dmd = (DatabaseMetaData) conn.getMetaData();
     while((readstr=brr.readLine())!=null)                     // TO USE IT HERE
    {
     ResultSet rs = dmd.getTables(null,"MigrationDB", "example", null);
     //set not null column
     if (String.valueOf(readstr).contains("NO"))
  readstr=readstr.replaceAll("NO", "not null");
     else if(String.valueOf(readstr).contains("YES"))
       readstr=readstr.replaceAll("YES", "");
     if(String.valueOf(readstr).contains("PRIMARY"))
         readstr=readstr.replaceFirst("PRIMARY","primary key");
    System.out.println("replace string "+readstr);
  int k=1;
   if (!rs.next())
  {
  stmt.executeUpdate("CREATE TABLE "+tname+ "("+readstr+")");

    }
 else{
     System.out.println(readstr);
     stmt.executeUpdate("ALTER TABLE "+tname+ " ADD("+readstr+")");
      System.out.println("altered");

      }
     }

    }
     catch (Exception e){}

   }


    }

Thank You.

解决方案

You need to understand what local variables are and what is their lifetime. I suggest reading through this tutorial: http://www.tutorialspoint.com/java/java_variable_types.htm

In you case, just declaring readstr outside the for loop would do what you want.

String readstr;
for(//loop condition) {
readstr = read value ;
}

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