Java for Testers – Interview Questions and Answers Part-3
1) Write a Java program to demonstrate the creation of Interface?
// A simple interface interface A { final int a = 10; void display(); } // A class that implements the interface. class TestClass implements A { public void display() { System.out.println("this is an interface"); } public static void main (String[] args) { TestClass t = new TestClass(); t.display(); System.out.println(a); } }
2) Write a Java program to print date and time?
public class CurrentDateTime { public static void main(String[] args) { DateTimeFormatter df = DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss"); LocalDateTime now = LocalDateTime.now(); System.out.println(df.format(now)); } }
3) Write a Java program to demonstrate SQL Date?
public class SQLDate { public static void main(String[] args) { long millis=System.currentTimeMillis(); java.sql.Date date=new java.sql.Date(millis); System.out.println(date); } }
4) Write a Java program to demonstrate Date format?
public class GetCurrentDateTime { private static final DateFormat sdf = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss"); private static final DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss"); public static void main(String[] args) { Date date = new Date(); System.out.println(sdf.format(date)); Calendar cal = Calendar.getInstance(); System.out.println(sdf.format(cal.getTime())); LocalDateTime now = LocalDateTime.now(); System.out.println(dtf.format(now)); LocalDate localDate = LocalDate.now(); System.out.println(DateTimeFormatter.ofPattern("yyy/MM/dd").format(localDate)); } }
5) Write a Java program to demonstrate generating a random number?
public class GenerateRandomNumber { public static void main(String[] args){ Random rand = new Random(); int r1 = rand.nextInt(1000); System.out.println("Random numbers: "+ r1); } }
6) Write a Java program to demonstrate garbage collection?
public class GarbageCollector { public static void main(String[] args) throws InterruptedException{ GarbageCollector t1 = new GarbageCollector(); GarbageCollector t2 = new GarbageCollector(); // Nullifying the reference variable t1 = null; // requesting JVM for running Garbage Collector System.gc(); // Nullifying the reference variable t2 = null; // Requesting JVM for running Garbage Collector Runtime.getRuntime().gc(); } @Override protected void finalize() throws Throwable { System.out.println("Garbage collector called"); System.out.println("Object garbage collected: " + this); } }
7) Write a Java program to get the IP Address of own machine?
public class FindIPAddress { public static void main(String[] args) throws Exception{ // Returns the instance of InetAddress containing local host name and address InetAddress localhost = InetAddress.getLocalHost(); System.out.println("System IP Address : " + (localhost.getHostAddress()).trim()); // Find public IP address String systemipaddress = ""; try { URL url_name = new URL("http://bot.whatismyipaddress.com"); BufferedReader sc = new BufferedReader(new InputStreamReader(url_name.openStream())); // reads system IPAddress systemipaddress = sc.readLine().trim(); } catch (Exception e) { systemipaddress = "Cannot Execute Properly"; } System.out.println("Public IP Address: " + systemipaddress +"\n"); } }
8) Write a Java program to open a notepad?
public class OpenNotepad { public static void main(String[] args){ Runtime rs = Runtime.getRuntime(); try{ rs.exec("notepad"); } catch (IOException e){ System.out.println(e); } } }
9) Write a Java program to demonstrate Linear Search?
public class LinearSearch { static int search(int arr[], int n, int x){ for(int i = 0;i<n;i++){ if(arr[i] == x) return i; } return -1; } public static void main(String[] args){ int[] arr = {5,1,9,4,3,8}; int n = arr.length; int x = 4; int index = search(arr,n,x); if(index == -1){ System.out.println("Element is not present in the array"); } else System.out.println("Element found at position " + index); } }
10) Write a Java program to demonstrate Binary Search?
class BinarySearch { int binarySearch(int arr[], int l, int r, int x) { if (r >= l) { int mid = l + (r - l) / 2; // If the element is present at the middle itself if (arr[mid] == x) return mid; // If element is smaller than mid, then it can only be present in left subarray if (arr[mid] > x) return binarySearch(arr, l, mid - 1, x); // Else the element can only be present in right subarray return binarySearch(arr, mid + 1, r, x); } // If element is not present in array return -1; } public static void main(String args[]) { BinarySearch bs = new BinarySearch(); int arr[] = { 2, 3, 4, 10, 40 }; int n = arr.length; int x = 10; int result = bs.binarySearch(arr, 0, n - 1, x); if (result == -1) System.out.println("Element not present"); else System.out.println("Element found at index " + result); } }
11) Write a Java program to demonstrate Bubble sort?
class BubbleSort { void bubbleSort(int arr[]) { int n = arr.length; for (int i = 0; i < n-1; i++) for (int j = 0; j < n-i-1; j++) if (arr[j] > arr[j+1]) { int temp = arr[j]; arr[j] = arr[j+1]; arr[j+1] = temp; } } void printArray(int arr[]) { int n = arr.length; for (int i=0; i<n; ++i) System.out.print(arr[i] + " "); System.out.println(); } public static void main(String args[]) { BubbleSort bs = new BubbleSort(); int arr[] = {64, 34, 25, 12, 22, 11, 90}; bs.bubbleSort(arr); System.out.println("Sorted array"); bs.printArray(arr); } }
12) Write a Java program to demonstrate connecting to a Database?
public class ConnectMSSQLServer { public void dbConnect(String db_connect_string,String db_userid,String db_password) { try { Class.forName("com.microsoft.sqlserver.jdbc.SQLServerDriver"); Connection conn = DriverManager.getConnection(db_connect_string,db_userid, db_password); System.out.println("connected"); Statement statement = conn.createStatement(); String queryString = "select * from Employees where lastName='Smith'"; ResultSet rs = statement.executeQuery(queryString); while (rs.next()) { System.out.println(rs.getString(1)); } } catch (Exception e) { e.printStackTrace(); } } public static void main(String[] args) { ConnectMSSQLServer connServer = new ConnectMSSQLServer(); connServer.dbConnect("jdbc:sqlserver://<hostname>", "<user>","<password>"); } }
13) Write a Java program to demonstrate inserting data into a table using JDBC?
public class InsertIntoDB { public static void main(String[] args) { Connection connection = null; Statement stmt = null; try { Class.forName("com.mysql.jdbc.Driver"); connection = DriverManager .getConnection("jdbc:mysql://localhost:3306/JDBCDemo", "root", "password"); stmt = connection.createStatement(); stmt.execute("INSERT INTO EMPLOYEE (ID,FIRST_NAME,LAST_NAME,STAT_CD) " + "VALUES (1,'John','Smith',5)"); } catch (Exception e) { e.printStackTrace(); }finally { try { stmt.close(); connection.close(); } catch (Exception e) { e.printStackTrace(); } } } }
14) Write a Java program to demonstrate executing a Procedure in JDBC?
public class StoredProcedureCallExample1 { public static void main(String[] args) { String dbURL = "jdbc:mysql://localhost:3306/booksdb"; String user = "root"; String password = "P@ssw0rd"; try ( Connection conn = DriverManager.getConnection(dbURL, user, password); CallableStatement statement = conn.prepareCall("{call create_author(?, ?)}"); ) { statement.setString(1, "Bill Gates"); statement.setString(2, "[email protected]"); statement.execute(); statement.close(); System.out.println("Stored procedure called successfully!"); } catch (SQLException ex) { ex.printStackTrace(); } } }
15) Write a Java program to check Regular Expressions?
class CheckRegularExpression{ public static void main(String []args){ Pattern pattern = Pattern.compile("auto*"); Matcher m = pattern.matcher("automation"); while (m.find()) System.out.println("Pattern found from " + m.start() + " to " + (m.end()-1)); } }
16) Write a Java program to create Multi-threading?
class Multithreading extends Thread { public void run() { try { // Displaying the thread that is running System.out.println ("Thread " + Thread.currentThread().getId() + " is running"); } catch (Exception e) { System.out.println ("Exception is caught"); } } } public class Multithread { public static void main(String[] args) { int n = 8; // Number of threads for (int i=0; i<8; i++) { Multithreading object = new Multithreading(); object.start(); } } }
17) Write a Java program to demonstrate joining thread?
public class JoinThreads { public static void main(String args[]) throws InterruptedException{ System.out.println(Thread.currentThread().getName() + " is Started"); Thread exampleThread = new Thread(){ public void run(){ try { System.out.println(Thread.currentThread().getName() + " is Started"); Thread.sleep(2000); System.out.println(Thread.currentThread().getName() + " is Completed"); } catch (InterruptedException ex) { Logger.getLogger(Join.class.getName()).log(Level.SEVERE, null, ex); } } } exampleThread.start(); exampleThread.join(); System.out.println(Thread.currentThread().getName() + " is Completed"); } }
18) Write a Java program to write data into the text files?
public static void WriteTextFile() throws IOException { String fileContent = "This is Java interview questions"; BufferedWriter writer = new BufferedWriter(new FileWriter("c:/temp/samplefile.txt")); writer.write(fileContent); writer.close(); }
19) Write a Java program to read data from the text files?
public class ReadTextAsString { public static String readFileAsString(String fileName)throws Exception { String data = ""; data = new String(Files.readAllBytes(Paths.get(fileName))); return data; } public static void main(String[] args) throws Exception { String data = readFileAsString("C:\\temp\\test.java"); System.out.println(data); } }
20) Write a Java program to convert string to integer?
public class ConvertStringToInteger{ public static void main(String[] args){ String number = "10"; int result = Integer.parseInt(number); System.out.println(result); } }
21) Write a Java program to convert integer to string?
public class ConvertIntegerToString{ public static void main(String[] args){ int a = 100 String str = Integer.toString(a); System.out.println(str); } }
22) Write a Java program to convert string to long?
public class ConvertStringToLong{ public static void main(String[] args){ String s = "10"; long result = Long.parseLong(s); System.out.println(result); } }
23) Write a Java program to convert string to float?
public class ConvertStringToLong{ public static void main(String[] args){ String s = "13.6"; float result = Float.parseFloat(s); System.out.println(result); } }
24) Write a Java program to convert string to double?
public class ConvertStringToDouble{ public static void main(String[] args){ String s = "6.54"; double result = Double.parseDouble(s); System.out.println(result); } }
25) Write a Java program to convert string to date?
public class StringToDate { public static void main(String[] args)throws Exception { String sDate="01/01/2020"; Date date=new SimpleDateFormat("dd/MM/yyyy").parse(sDate); System.out.println(sDate+"\t"+date); } }
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