ghzdb.java

java 简单模拟DBMS功能

import java.io.BufferedReader;
import java.io.File;
import java.io.InputStreamReader;

/*
保存、打开数据库；
添加、删除表；
添加、删除行；
添加、删除列；
 */
public class ghzDB {
  clsDatabase db = new clsDatabase();
  public static void main(String args[]) {
    ghzDB ghzdb = new ghzDB();
    System.out.println("\n*****************************");
    
    System.out.println("*****************************");
    
    System.out.println("\n\nYou can input 'help' to get help\n\n");
    String usrinp = new String();
    String temp = new String();
    BufferedReader input = new BufferedReader(new InputStreamReader(
        System.in));

    while (!usrinp.equals("exit")) {
      System.out.print("GHZDB->");
      try {
        usrinp = input.readLine();
        usrinp = usrinp.toLowerCase();
        if (usrinp.equals("exit")) {
          System.exit(0);
        }
        else if (usrinp.equals("modifydbname")) {
          System.out.println("Input new Database name:");
          temp = input.readLine();
          ghzdb.db.setName(temp);
        }
        else if (usrinp.equals("addtable")) {
          System.out.println("Input new table name:");
          temp = input.readLine();
          ghzdb.db.add_table(temp);
        }
        else if (usrinp.equals("deltable")) {
          System.out.println("Input delete table name:");
          temp = input.readLine();
          ghzdb.db.del_table(temp);
        }
        else if (usrinp.equals("addfield")) {
          System.out.println("Input table name:");
          temp = input.readLine();
          String temp2 = new String();
          System.out.println("Input new field name:");
          temp2 = input.readLine();
          ghzdb.db.add_field(temp, temp2);
        }
        else if (usrinp.equals("delfield")) {
          System.out.println("Input table name:");
          temp = input.readLine();
          String temp2 = new String();
          System.out.println("Input delete field name:");
          temp2 = input.readLine();
          ghzdb.db.del_field(temp, temp2);
        }
        else if (usrinp.equals("printall")) {
          System.out.println(ghzdb.db.return_all());
        }
        else if (usrinp.equals("modifytblname")) {
          System.out.println("Input old table name:");
          temp = input.readLine();
          String temp2 = new String();
        }
        else if (usrinp.equals("addrow")) {
          System.out.println("Input table name:");
          temp = input.readLine();
          String addrowval[] = new String[ghzdb.db
              .getFieldCount(temp)];
          for (int i = 0; i < ghzdb.db.getFieldCount(temp); i++) {
            System.out.println("Input field "
                               + ghzdb.db.getFieldName(temp, i) + " value:");
            addrowval[i] = input.readLine();
          }
          ghzdb.db.add_row(temp, addrowval);
        }
        else if (usrinp.equals("delrow")) {
          System.out.println("Input table name:");
          temp = input.readLine();
          String temp2, temp3;
          System.out.println("Input field name");
          temp2 = input.readLine();
          System.out.println("Input field value");
          temp3 = input.readLine();
          ghzdb.db.del_row(temp, temp2, temp3);
        }
        else if (usrinp.equals("savedb")) {
          System.out.println("Input file name:");
          temp = input.readLine();
          ghzdb.db.saveDB(temp);
        }
        else if (usrinp.equals("opendb")) {
          System.out.println("Input file name:");
          temp = input.readLine();
          File file = new File(temp);
          if (file.exists() == true) {
            ghzdb.db.openDB(temp);
          }
          else {
            System.out.println("Can't find this file!!!");
          }
        }
        else if (usrinp.equals("help")) {
          System.out.println("************************************");
          System.out.println("*          Command List            *");
          System.out.println("************************************");
          System.out.println("*modifydbname:modify database name *");
          System.out.println("************************************");
          System.out.println("*     addtable:add a table         *");
          System.out.println("************************************");
          System.out.println("*     deltable:delete a table      *");
          System.out.println("************************************");
          System.out.println("*      addfield:add a field        *");
          System.out.println("************************************");
          System.out.println("*     delfield:delete a field      *");
          System.out.println("************************************");
          System.out.println("*         addrow:add a row         *");
          System.out.println("************************************");
          System.out.println("*         delrow:del a row         *");
          System.out.println("************************************");
          System.out.println("* mdoifytblname:modify table name  *");
          System.out.println("************************************");
          System.out.println("*printall:print all table,field,row*");
          System.out.println("************************************");
          System.out.println("*   savedb:save database to file   *");
          System.out.println("************************************");
          System.out.println("*  opendb:open database from file  *");
          System.out.println("************************************");
          System.out.println("*  getmemfree:get memory free size *");
          System.out.println("************************************");
          System.out.println("\n");
        }
        else if (usrinp.equals("getmemfree")) {
          System.out.println(Runtime.getRuntime().freeMemory()
                             + " Program Memory free");
        }
        else if (usrinp.equals("")) {
        }
        else {
          System.out.println("Unknow Command!!!");
        }
      }
      catch (Exception e) {

      }
      finally {
        if (ghzdb.db.getErrorMessage().equals("")) {
          System.out.println("Finish this work!!!");
        }
        else if (ghzdb.db.getErrorMessage().indexOf("Index") == -1) {
          System.out.println(ghzdb.db.getErrorMessage());
          ghzdb.db.setErrorMessageEmpty();
        }
      }
    }
  }
}