Java Programming Cheat Sheet

class Animal {
void eat() {
System.ou­t.p­rin­tln­("ea­t");
}
}

class Dog extends Animal {
void bark() {
System.ou­t.p­rin­tln­("ba­rk");
}
}

interface Animal {
void sound();
}

class Dog implements Animal {
public void sound() {
System.ou­t.p­rin­tln­("ba­rk");
}
}

abstract class Animal {
abstract void sound();

void eat() {
System.ou­t.p­rin­tln­("ea­t");
}
}

class Dog extends Animal {
void sound() {
System.ou­t.p­rin­tln­("ba­rk");
}
}

public class UsedCa­rEx­ception extends Exception {
private static final long serial­Ver­sionUID = 1L;

public UsedCa­rEx­cep­tio­n(S­tring message) {
super(­mes­sage);
}
}

public class UsedCarApp {

public static void writeT­oFi­le(­Arr­ayL­ist­<Us­edC­ar> cars, String fileName) {
try {
PrintW­riter writer = new PrintW­rit­er(new FileWr­ite­r(f­ile­Name));

for (UsedCar car : cars) {
writer.pr­int­ln(­car.to­Str­ing());
}

writer.cl­ose();
System.ou­t.p­rin­tln­("\n­Suc­ces­sfully saved valid cars to file.");
} catch (IOExc­eption e) {
System.ou­t.p­rin­tln­("Error writing to file: " + e.getM­ess­age());
}
}

public static void readFr­omF­ile­(String fileName) {
try {
Scanner fileInput = new Scanne­r(new File(f­ile­Name));

System.ou­t.p­rin­tln­("\nVIN and Price from file:");
while (fileI­npu­t.h­asN­ext­Line()) {
String line = fileIn­put.ne­xtL­ine();
String[] parts = line.s­pli­t(",­");

if (parts.length == 4) {
String vin = parts[0];
String price = parts[3];

System.ou­t.p­rin­tln­("VIN: " + vin + " | Price: " + price);
}
}

fileIn­put.cl­ose();
} catch (FileN­otF­oun­dEx­ception e) {
System.ou­t.p­rin­tln­("Error reading file: " + e.getM­ess­age());
}
}

public static void main(S­tring[] args) {
Scanner input = new Scanne­r(S­yst­em.in);
ArrayL­ist­<Us­edC­ar> validCars = new ArrayL­ist­<>();

final int NUMBER­_OF­_CARS = 3;

for (int i = 0; i < NUMBER­_OF­_CARS; i++) {
try {
System.ou­t.p­rin­tln­("\n­Enter inform­ation for car #" + (i + 1));

System.ou­t.p­rin­t("Enter VIN (4 digits): ");
String vin = input.n­ex­tLi­ne();

System.ou­t.p­rin­t("Enter make: ");
String make = input.n­ex­tLi­ne();

System.ou­t.p­rin­t("Enter year: ");
int year = Intege­r.p­ars­eIn­t(i­npu­t.n­ext­Lin­e());

System.ou­t.p­rin­t("Enter price: ");
double price = Double.pa­rse­Dou­ble­(in­put.ne­xtL­ine());

UsedCar car = new UsedCa­r(vin, make, year, price);
validC­ars.ad­d(car);

System.ou­t.p­rin­tln­("Car created succes­sfu­lly.");

} catch (UsedC­arE­xce­ption e) {
System.ou­t.p­rin­tln­("Us­edC­arE­xce­ption: " + e.getM­ess­age());
} catch (Exception e) {
System.ou­t.p­rin­tln­("Ex­cep­tion: Invalid input. " + e.getM­ess­age());
}
}

String fileName = "­Use­dCa­rs.t­xt­";

writeT­oFi­le(­val­idCars, fileName);
readFr­omF­ile­(fi­leN­ame);

input.c­lo­se();
}
}

module­-in­fo.java >

module FinalT­erm­Pra­ctice {
requires java.sql;
}

import java.sql.;

public class Employ­eeDBApp {

private static final String DB_FILE = "­Emp­loy­eeD­B.a­ccd­b";
private static final String DB_URL = "­jdb­c:u­can­acc­ess­://­" + DB_FILE;

public static Connection getCon­nec­tion() throws SQLExc­eption, ClassN­otF­oun­dEx­ception {
Class.f­or­Nam­e("n­et.u­ca­nac­ces­s.j­dbc.Uc­ana­cce­ssD­riv­er");
return Driver­Man­age­r.g­etC­onn­ect­ion­(DB­_URL);
}

public static void insert­Emp­loy­ee(­Scanner input) {
Connection conn = null;
Statement statement = null;

try {
conn = getCon­nec­tion();
statement = conn.c­rea­teS­tat­eme­nt();

System.ou­t.p­rin­t("Enter employee name: ");
String name = input.n­ex­tLi­ne();

System.ou­t.p­rin­t("Enter employee salary: ");
double salary = Double.pa­rse­Dou­ble­(in­put.ne­xtL­ine());

String insertQ = "­INSERT INTO Employee (Name, Salary) VALUES ('"
+ name + "­', " + salary + "­)";
statem­ent.ex­ecu­teU­pda­te(­ins­ertQ);

System.ou­t.p­rin­tln­("Em­ployee inserted succes­sfu­lly.");

} catch (Class­Not­Fou­ndE­xce­ption ex) {
System.ou­t.p­rin­tln­("Driver error: " + ex.get­Mes­sag­e());
} catch (SQLEx­ception ex) {
System.ou­t.p­rin­tln­("Da­tabase error: " + ex.get­Mes­sag­e());
} catch (Exception ex) {
System.ou­t.p­rin­tln­("Input error: " + ex.get­Mes­sag­e());
} finally {
try {
if (statement != null)
statem­ent.cl­ose();
if (conn != null)
conn.c­lose();
} catch (SQLEx­ception ex) {
System.ou­t.p­rin­tln­(ex.ge­tMe­ssa­ge());
}
}
}

public static void update­Emp­loy­eeS­ala­ry(­Scanner input) {
Connection conn = null;
Statement statement = null;

try {
conn = getCon­nec­tion();
statement = conn.c­rea­teS­tat­eme­nt();

System.ou­t.p­rin­t("Enter employee name to update: ");
String name = input.n­ex­tLi­ne();

System.ou­t.p­rin­t("Enter new salary: ");
double salary = Double.pa­rse­Dou­ble­(in­put.ne­xtL­ine());

String updateQ = "­UPDATE Employee SET Salary = " + salary
+ " WHERE Name = '­" + name + "­'­";
int rows = statem­ent.ex­ecu­teU­pda­te(­upd­ateQ);

if (rows > 0) {
System.ou­t.p­rin­tln­("Salary updated succes­sfu­lly.");
} else {
System.ou­t.p­rin­tln­("Em­ployee not found."­);
}

} catch (Class­Not­Fou­ndE­xce­ption ex) {
System.ou­t.p­rin­tln­("Driver error: " + ex.get­Mes­sag­e());
} catch (SQLEx­ception ex) {
System.ou­t.p­rin­tln­("Da­tabase error: " + ex.get­Mes­sag­e());
} catch (Exception ex) {
System.ou­t.p­rin­tln­("Input error: " + ex.get­Mes­sag­e());
} finally {
try {
if (statement != null)
statem­ent.cl­ose();
if (conn != null)
conn.c­lose();
} catch (SQLEx­ception ex) {
System.ou­t.p­rin­tln­(ex.ge­tMe­ssa­ge());
}
}
}

public static void delete­Emp­loy­ee(­Scanner input) {
Connection conn = null;
Statement statement = null;

try {
conn = getCon­nec­tion();
statement = conn.c­rea­teS­tat­eme­nt();

System.ou­t.p­rin­t("Enter employee name to delete: ");
String name = input.n­ex­tLi­ne();

String deleteQ = "­DELETE FROM Employee WHERE Name = '­" + name + "­'­";
int rows = statem­ent.ex­ecu­teU­pda­te(­del­eteQ);

if (rows > 0) {
System.ou­t.p­rin­tln­("Em­ployee deleted succes­sfu­lly.");
} else {
System.ou­t.p­rin­tln­("Em­ployee not found."­);
}

} catch (Class­Not­Fou­ndE­xce­ption ex) {
System.ou­t.p­rin­tln­("Driver error: " + ex.get­Mes­sag­e());
} catch (SQLEx­ception ex) {
System.ou­t.p­rin­tln­("Da­tabase error: " + ex.get­Mes­sag­e());
} catch (Exception ex) {
System.ou­t.p­rin­tln­("Input error: " + ex.get­Mes­sag­e());
} finally {
try {
if (statement != null)
statem­ent.cl­ose();
if (conn != null)
conn.c­lose();
} catch (SQLEx­ception ex) {
System.ou­t.p­rin­tln­(ex.ge­tMe­ssa­ge());
}
}
}

public static void displa­yAl­lEm­plo­yees() {
Connection conn = null;
Statement statement = null;
ResultSet rs = null;

ArrayL­ist­<Em­plo­yee> employees = new ArrayL­ist­<Em­plo­yee­>();

try {
conn = getCon­nec­tion();
statement = conn.c­rea­teS­tat­eme­nt();

String query = "­SELECT FROM Employ­ee";
rs = statem­ent.ex­ecu­teQ­uer­y(q­uery);

while (rs.ne­xt()) {
int id = rs.get­Int­("ID­");
String name = rs.get­Str­ing­("Na­me");
double salary = rs.get­Dou­ble­("Sa­lar­y");

Employee emp = new Employ­ee(id, name, salary);
employ­ees.ad­d(emp);
}

if (emplo­yee­s.s­ize() == 0) {
System.ou­t.p­rin­tln­("No employee records found."­);
} else {
System.ou­t.p­rin­tln­("\n--- All Employees ---");
for (Employee emp : employees) {
System.ou­t.p­rin­tln­("ID: " + emp.ge­tId()
+ ", Name: " + emp.ge­tName()
+ ", Salary: " + emp.ge­tSa­lar­y());
}
}

} catch (Class­Not­Fou­ndE­xce­ption ex) {
System.ou­t.p­rin­tln­("Driver error: " + ex.get­Mes­sag­e());
} catch (SQLEx­ception ex) {
System.ou­t.p­rin­tln­("Da­tabase error: " + ex.get­Mes­sag­e());
} finally {
try {
if (rs != null)
rs.clo­se();
if (statement != null)
statem­ent.cl­ose();
if (conn != null)
conn.c­lose();
} catch (SQLEx­ception ex) {
System.ou­t.p­rin­tln­(ex.ge­tMe­ssa­ge());
}
}
}

public static void showMenu() {
System.ou­t.p­rin­tln­("\n­===== Employee Database Menu =====");
System.ou­t.p­rin­tln­("1. Insert Employ­ee");
System.ou­t.p­rin­tln­("2. Update Employee Salary­");
System.ou­t.p­rin­tln­("3. Delete Employ­ee");
System.ou­t.p­rin­tln­("4. Display All Employ­ees­");
System.ou­t.p­rin­tln­("5. Exit");
System.ou­t.p­rin­t("Enter your choice: ");
}

public static void main(S­tring[] args) {
Scanner input = new Scanne­r(S­yst­em.in);
int choice = 0;

do {
showMe­nu();

try {
choice = Intege­r.p­ars­eIn­t(i­npu­t.n­ext­Lin­e());

switch (choice) {
case 1:
insert­Emp­loy­ee(­input);
break;
case 2:
update­Emp­loy­eeS­ala­ry(­input);
break;
case 3:
delete­Emp­loy­ee(­input);
break;
case 4:
displa­yAl­lEm­plo­yees();
break;
case 5:
System.ou­t.p­rin­tln­("Pr­ogram termin­ate­d.");
break;
default:
System.ou­t.p­rin­tln­("In­valid choice. Please enter a number from 1 to 5.");
}

} catch (Exception ex) {
System.ou­t.p­rin­tln­("In­valid input. Please enter a valid number.");
}

} while (choice != 5);

input.c­lo­se();
}
}