Java String, Matrix and MySQL JDBC Code Examples

Java String Manipulation

Private Attribute

private String lectura;

Obtain N Characters

// Obtain N characters

public String obtieneCar(int numCar) {
    String caract;
    caract = lectura.substring(0, numCar);
    return caract;
}

Check String

// Check whether a substring is contained

public boolean compruebaString(String sub) {
    if (lectura.contains(sub)) {
        return true;
    } else {
        return false;
    }
}

Count Characters

// Count occurrences of a character

public int cuentaCar(char car) {
    int contador = 0;
    for (int i = 0; i < lectura.length(); i++) {
        if (lectura.charAt(i) == car) {
            contador++;
        }
    }
    return contador;
}

Reverse Reading

// Read the string backwards

public String cadenaAlReves() {
    String lecturaReves = "";
    for (int i = lectura.length() - 1; i >= 0; i--) {
        lecturaReves = lecturaReves + lectura.charAt(i);
    }
    return lecturaReves;
}

Matrix Class

Attributes

private int fil;
private int col;
private int matrizEnt[][];

Fill Matrix from Keyboard

public void rellenarMatriz() {
    Scanner sc = new Scanner(System.in);
    System.out.println("Introduce filas");
    fil = sc.nextInt();
    System.out.println("Introduce columnas");
    col = sc.nextInt();
    matrizEnt = new int[fil][col];
    for (int x = 0; x < matrizEnt.length; x++) {
        for (int y = 0; y < matrizEnt[x].length; y++) {
            System.out.println("Escriba el valor para la fila " + (x + 1) + " y la columna " + (y + 1));
            matrizEnt[x][y] = sc.nextInt();
        }
    }
}

Display Matrix

public void mostrar() {
    for (int i = 0; i < matrizEnt.length; i++) {
        System.out.println("");
        for (int j = 0; j < matrizEnt[i].length; j++) {
            System.out.print(matrizEnt[i][j] + " ");
        }
    }
}

Database Connection

Query and JDBC Connection

String query = "SELECT nombre, apellido1 FROM empleados WHERE ciudad = 'Almería'";
try {
    // 1. Create connection
    Connection miConexion = DriverManager.getConnection("jdbc:mysql://localhost:3306/practica6", "root", "12123456");
    // 2. Create statement object
    Statement miStatement = miConexion.createStatement();
    // 3. Execute the SQL statement
    ResultSet miResultset = miStatement.executeQuery(query);
    // 4. Iterate over the result set
    while (miResultset.next()) {
        System.out.println(miResultset.getString("nombre") + " " + miResultset.getString("apellido1"));
    }
} catch (Exception e) {
    System.out.println("No conecta");
    e.printStackTrace();
}