Java Code Snippets: Database, Lambda, and String Operations

Submit Method

This method handles database connection and data retrieval.

    
      public String Submit() {
        try {
          Class.forName("com.mysql.jdbc.Driver");
          System.out.println("Driver is ok.");
        } catch (ClassNotFoundException e) {
          System.out.println(e.getMessage());
        }
        try {
          c = DriverManager.getConnection(DB_Url, dbusername, password);
          s = c.createStatement();
          /*String Query1 = "insert into practice (rollNumber,studName,Date,username,pwd,email,phone) "
          + "values('1','" + this.studName + "','1234','" + this.username + "','" + this.pwd + "','" + this.email + "','123')";
          s.executeUpdate(Query1);*/
          /*String Query1 = "select * from practice";
          Student st;
          ArrayList<Student> arr = new ArrayList<Student>();
          rset = s.executeQuery(Query1);
          while (rset.next()) {
            st = new Student();
            st.rollNumber = rset.getInt(1);
            st.studName = rset.getString(2);
            arr.add(st);
            System.out.println("Success");
          }
          for(int i=0;i<arr.size();i++){
            System.out.println(arr.get(i).rollNumber + " " + arr.get(i).studName);
          }*/
        } catch (SQLException e) {
          errorMsg = e.getMessage();
        } finally {
          try {
            //rset.close();
            s.close();
            c.close();
          } catch (Exception e) {
            e.printStackTrace();
          }
        }
        return "Log";
      }
    
  

Hotel Data Retrieval

This section retrieves hotel and room data from the database.

    
      try {
        c = DriverManager.getConnection(DB_Url, dbusername, password);
        s = c.createStatement();
        String Query1 = "select * from hotel";
        rset = s.executeQuery(Query1);
        while (rset.next()) {
          hp = new HotelApp();
          hp.HotelId = rset.getInt(1);
          hp.HotelName = rset.getString(2);
          System.out.println(rset.getInt(1));
          System.out.println(rset.getString(2));
          arr.add(hp);
        }
        for (int i = 0; i < arr.size(); i++) {
          if (arr.get(i).HotelName.equals(this.HotelName)) {
            String Query2 = "select * from hotelroom where hotelId='" + arr.get(i).HotelId + "' and status='Available'";
            rset = s.executeQuery(Query2);
            while (rset.next()) {
              hr = new HotelRooms();
              hr.setHotelId(rset.getInt(1));
              hr.setRoomId(rset.getInt(2));
              hr.setStatus(rset.getString(3));
              System.out.println(rset.getInt(1));
              System.out.println(rset.getInt(2));
              System.out.println(rset.getString(3));
              roomsarr.add(hr);
            }
          }
        }
      } catch (SQLException e) {
        errorMsg = e.getMessage();
      } finally {
        try {
          if (rset != null) rset.close();
          if (s != null) s.close();
          if (c != null) c.close();
        } catch (Exception e) {
          e.printStackTrace();
        }
      }
    
  

Lambda Expressions and Streams

Examples of using lambda expressions and streams for data processing.

Employee Data Processing

Examples of using streams to process employee data.

    
      Emp[] e = {
        new Emp("Alice","Edward",18,50000),
        new Emp("Alice","Jones",18,2000),
        new Emp("Alice","Edward",18,300)
      };
    
  

Text Processing with Streams

Examples of using streams to process text data.

Random Number Generation

Example of generating random numbers using SecureRandom.

Date Formatting and Parsing

Examples of formatting and parsing dates.

    
      try {
        String startDateString = "07/30/2016";
        DateFormat df = new SimpleDateFormat("MM/dd/yyyy");
        Date startDate = df.parse(startDateString);
        System.out.println("Date, with the default formatting: " + startDate);
        Date today = new Date();
        System.out.println("today is: " + today);
        if (today.after(startDate)) {
          System.out.println("success");
        } else {
          System.out.println("fail");
        }
      } catch (ParseException e) {
        e.printStackTrace();
      }
    
  

Unique Digits Count

Algorithm to count numbers with unique digits.

    
      public class Solution {
        public int countNumbersWithUniqueDigits(int n) {
          int[] count = new int[11];
          count[0] = 1;
          count[1] = 10;
          int max = (n > 10) ? 10 : n;
          int temp = 9;
          for (int i = 2; i <= max; i++) {
            temp = temp * (11 - i);
            count[i] = count[i - 1] + temp;
          }
          return count[max];
        }
      }
    
  

String Multiplication

Algorithm to multiply two strings representing numbers.

    
      public String multiply(String num1, String num2) {
        String n1 = new StringBuilder(num1).reverse().toString();
        String n2 = new StringBuilder(num2).reverse().toString();
        int[] d = new int[num1.length()+num2.length()];
        for(int i=0; i<n1.length(); i++){
          for(int j=0; j<n2.length(); j++){
            d[i+j] += (n1.charAt(i)-'0') * (n2.charAt(j)-'0');
          }
        }
        StringBuilder sb = new StringBuilder();
        for(int i=0; i<d.length; i++){
          int mod = d[i]%10;
          int carry = d[i]/10;
          if(i+1<d.length){
            d[i+1] += carry;
          }
          sb.insert(0, mod);
        }
        while(sb.charAt(0) == '0' && sb.length()> 1){
          sb.deleteCharAt(0);
        }
        return sb.toString();
      }
    
  

Comparator Examples

Examples of using comparators for sorting.

Grouping Employees by Department

Examples of grouping employees by department.

Counting Employees per Department

Examples of counting employees in each department.