Java

https://www.geeksforgeeks.org/java/
Admin
Java is a high-level, object-oriented programming language used to build web apps, mobile...
Tokens:285,866
Snippets:3,089
Trust Score:10
Update:1 month ago
Show doc for...
Tokens:
Raw
### Setup MySQL Database Schema

Source: https://www.geeksforgeeks.org/java/jdbc-tutorial

SQL commands to create the school database and students table for the JDBC example.

```sql
CREATE DATABASE school;
USE school;

CREATE TABLE students (
    id INT PRIMARY KEY,
    name VARCHAR(50),
    age INT
);

INSERT INTO students VALUES (1, 'Amit', 21), (2, 'Riya', 22);
```

--------------------------------

### Complete Connection Example

Source: https://www.geeksforgeeks.org/java/connection-interface-in-java-jdbc

A full example demonstrating how to establish and close a database connection in Java.

```java
import java.sql.Connection;
import java.sql.DriverManager;

class ConnectionDemo {
    public static void main(String[] args) {
        try {
            Connection con = DriverManager.getConnection(
                "jdbc:mysql://localhost:3306/test",
                "root",
                "password"
            );

            System.out.println("Connection Established Successfully!");

            con.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}
```

--------------------------------

### HashSet Constructor Examples

Source: https://www.geeksforgeeks.org/java/hashset-in-java

Syntax examples for the various constructors available in the HashSet class.

```java
HashSet<String> set = new HashSet<>();
```

```java
HashSet<Type> set = new HashSet<>( initialCapacity);
```

```java
HashSet<Type> set = new HashSet<>( initialCapacity, loadFactor);
```

```java
HashSet<Type> set = new HashSet<>(c);
```

--------------------------------

### Display Private Constructor Example Output

Source: https://www.geeksforgeeks.org/java/java-interview-questions

The expected console output after executing the singleton pattern example.

```text
Value of a.x = 20
Value of b.x = 20
```

--------------------------------

### Demonstrating ConcurrentSkipListSet Operations

Source: https://www.geeksforgeeks.org/java/concurrentskiplistset-in-java-with-examples

This example shows how to initialize a ConcurrentSkipListSet, add elements, retrieve the last element, poll the first element, check for existence, and get the size.

```java
class ConcurrentSkipListSetLastExample1 {
    public static void main(String[] args)
    {
        // Initializing the set using
        // ConcurrentSkipListSet()
        ConcurrentSkipListSet<Integer> set
            = new ConcurrentSkipListSet<Integer>();

        // Adding elements to this set
        // using add() method
        set.add(78);
        set.add(64);
        set.add(12);
        set.add(45);
        set.add(8);

        // Printing the ConcurrentSkipListSet
        System.out.println("ConcurrentSkipListSet: " + set);

        // Printing the highest element of the set
        // using last() method
        System.out.println(
            "The highest element of the set: "
            + set.last());

        // Retrieving and removing first element of the set
        System.out.println("The first element of the set: "
                           + set.pollFirst());

        // Checks if 9 is present in the set
        // using contains() method
        if (set.contains(9))
            System.out.println("9 is present in the set.");
        else
            System.out.println(
                "9 is not present in the set.");

        // Printing the size of the set
        // using size() method
        System.out.println(
            "Number of elements in the set = "
            + set.size());
    }
}
```

--------------------------------

### Executing a thread using start()

Source: https://www.geeksforgeeks.org/java/difference-between-thread-start-and-thread-run-in-java

Demonstrates how calling start() allocates resources and executes the run() method in a new thread.

```java
class MyThread extends Thread {

    public void run(){

        System.out.println("Thread running using start()");
    }

    public static void main(String[] args)
    {
        MyThread t1 = new MyThread();
        
        // Starts a new thread
        t1.start(); 
    }
}
```

--------------------------------

### Quiz Example: Multiple start() Calls

Source: https://www.geeksforgeeks.org/java/difference-between-thread-start-and-thread-run-in-java

A code snippet used in a quiz context to illustrate the behavior of calling start() twice on a thread instance.

```java
class MyThread extends Thread {
    public void run() {
        System.out.println("Running...");
    }
    
    public static void main(String[] args) {
        MyThread t = new MyThread();
        t.start();
        t.start();
    }
}
```

--------------------------------

### Access EnumMap Elements

Source: https://www.geeksforgeeks.org/java/enummap-class-java-example

Partial example demonstrating the setup for accessing elements using entrySet, keySet, values, and get.

```java
import java.util.EnumMap;
class Geeks {
    
    // Enum
    enum Color { RED, GREEN, BLUE, WHITE }
```

--------------------------------

### Demonstrate createNewFile() for a New File

Source: https://www.geeksforgeeks.org/java/file-createnewfile-method-in-java-with-examples

Example showing the creation of a file when the path does not already exist.

```java
// Java program to demonstrate
// createNewFile() method of File Class

import java.io.*;

public class solution {
    public static void main(String args[])
    {

        try {

            // Get the file
            File f = new File("F:\\program.txt");

            // Create new file
            // if it does not exist
            if (f.createNewFile())
                System.out.println("File created");
            else
                System.out.println("File already exists");
        }
        catch (Exception e) {
            System.err.println(e);
        }
    }
}
```

--------------------------------

### Initialize PriorityQueue and TreeSet

Source: https://www.geeksforgeeks.org/java/java-interview-questions

Instantiation examples for PriorityQueue and TreeSet collections.

```java
PriorityQueue<Integer> pq = new PriorityQueue<>();
```

```java
reeSet<Integer> ts = new TreeSet<>();
```

--------------------------------

### Demonstrate createNewFile() for an Existing File

Source: https://www.geeksforgeeks.org/java/file-createnewfile-method-in-java-with-examples

Example showing the behavior when the file path already exists.

```java
// Java program to demonstrate
// createNewFile() method of File Class

import java.io.*;

public class solution {
    public static void main(String args[])
    {

        try {

            // Get the file
            File f = new File("F:\\program1.txt");

            // Create new file
            // if it does not exist
            if (f.createNewFile())
                System.out.println("File created");
            else
                System.out.println("File already exists");
        }
        catch (Exception e) {
            System.err.println(e);
        }
    }
}
```

--------------------------------

### Full Example of Calling a Stored Procedure

Source: https://www.geeksforgeeks.org/java/how-to-use-callable-statement-in-java-to-call-stored-procedure

A complete example demonstrating the full lifecycle of calling a stored procedure using CallableStatement.

```java
import java.sql.*;

public class CallableExample {
    public static void main(String[] args) throws Exception {

        Class.forName("com.mysql.cj.jdbc.Driver");

        Connection con = DriverManager.getConnection(
            "jdbc:mysql://localhost:3306/testdb", "root", "password");

        // Calling stored procedure
        String sql = "{call insertStudent(?, ?, ?)}";

        CallableStatement cs = con.prepareCall(sql);

        cs.setString(1, "geek1");
        cs.setString(2, "python");
        cs.setString(3, "beginner");

        cs.execute();

        System.out.println("Stored procedure executed successfully");

        con.close();
    }
}
```

--------------------------------

### Comparable Example Output

Source: https://www.geeksforgeeks.org/java/comparable-interface-in-java-with-examples

The expected console output after running the ComparableExample class.

```text
Charlie: 78
Alice: 85
Bob: 92
```

--------------------------------

### Create and Populate an ArrayList

Source: https://www.geeksforgeeks.org/java/arraylist-in-java

Basic example demonstrating the instantiation of an ArrayList, adding elements, and printing the collection.

```java
import java.util.ArrayList;

class Main {
    public static void main (String[] args) {
        
      	// Creating an ArrayList
      	ArrayList<Integer> a = new ArrayList<>();
      	
      	// Adding Element in ArrayList
      	a.add(1);
      	a.add(2);
      	a.add(3);
      
      	// Printing ArrayList
      	System.out.println(a);
    }
}
```

--------------------------------

### Initialize BufferedReader

Source: https://www.geeksforgeeks.org/java/java-io-bufferedreader-class-java

Examples of initializing BufferedReader with default and custom buffer sizes.

```java
BufferedReader br = new BufferedReader(new FileReader("file.txt"));
```

```java
BufferedReader br = new BufferedReader(new FileReader("file.txt"), 8192);
```

--------------------------------

### Bounded Type Parameter Example Output

Source: https://www.geeksforgeeks.org/java/bounded-types-generics-java

The expected console output after running the bounded type example.

```text
Inside sub class C
Inside sub class B
Inside super class A
```

--------------------------------

### ArrayList Constructor Examples

Source: https://www.geeksforgeeks.org/java/arraylist-in-java

Demonstrates the three primary ways to initialize an ArrayList in Java.

```java
ArrayList<Integer> arr = new ArrayList<>();
```

```java
ArrayList<String> arr = new ArrayList<>(collection);
```

```java
ArrayList<Double> arr = new ArrayList<>(20);
```

--------------------------------

### Start a thread in Java

Source: https://www.geeksforgeeks.org/java/java-interview-questions

Initiates the execution of a thread.

```java
thread2.start();
```

--------------------------------

### Display StringBuffer output

Source: https://www.geeksforgeeks.org/java/java-interview-questions

The expected output of the StringBuffer example.

```text
GeeksforGeeks
```

--------------------------------

### Display String output

Source: https://www.geeksforgeeks.org/java/strings-in-java

Standard output result for the string creation example.

```text
Geeks
```

--------------------------------

### Demonstrate ArrayStoreException Output

Source: https://www.geeksforgeeks.org/java/java-interview-questions

The runtime exception output generated by the ArrayStoreException example.

```text
Exception in thread "main" java.lang.ArrayStoreException: java.lang.Integer  
    at GFG.main(GFG.java:6)
```

--------------------------------

### Demonstrate offerFirst() with Strings

Source: https://www.geeksforgeeks.org/java/blockingdeque-offerfirst-method-in-java-with-examples

This example demonstrates the usage of offerFirst() with a BlockingDeque containing String elements.

```java
// Java Program Demonstrate offerFirst()
// method of BlockingDeque

import java.util.concurrent.LinkedBlockingDeque;
import java.util.concurrent.BlockingDeque;
import java.util.*;

public class GFG {
    public static void main(String[] args)
        throws IllegalStateException
    {

        // create object of BlockingDeque
        BlockingDeque<String> BD
            = new LinkedBlockingDeque<String>(4);

        // Add numbers to end of BlockingDeque
        BD.offerFirst("abc");
        BD.offerFirst("gopu");
        BD.offerFirst("geeks");
        BD.offerFirst("richik");

        // Cannot be inserted
        BD.offerFirst("hii");

        // cannot be inserted hence returns false
        if (!BD.offerFirst("hii"))
            System.out.println("The element 'hii' cannot be"
                               + " inserted as capacity is full");

        // before removing print queue
        System.out.println("Blocking Deque: " + BD);
    }
}
```

--------------------------------

### Example Input for Arithmetic Program

Source: https://www.geeksforgeeks.org/java/java-arithmetic-operators-with-examples

Sample input values provided to the arithmetic program.

```text
Enter the first number: 20  
Enter the second number: 10
```

--------------------------------

### Output of notify() example

Source: https://www.geeksforgeeks.org/java/difference-between-notify-and-notifyall-in-java

The expected console output after executing the notify() demonstration code.

```text
Thread-1...start  
Thread-2...starts  
Thread-3...starts  
Thread-3...notified  
Thread-1...notified
```

--------------------------------

### LinkedHashSet Output

Source: https://www.geeksforgeeks.org/java/java-interview-questions

The expected console output after running the LinkedHashSet example.

```text
Values:[1, 2, 5, 3]
```

--------------------------------

### Demonstrate unmodifiableNavigableSet with Integers

Source: https://www.geeksforgeeks.org/java/java-collections-unmodifiablenavigableset%E2%80%8B-method-with-examples

Example showing how modifications to the backing set are reflected in the unmodifiable view.

```java
import java.util.*;
public class GFG1 {
    // main method
    public static void main(String[] args)
    {
        // create a set named data
        NavigableSet<Integer> data = new TreeSet<Integer>();
        // Add values in the data
        data.add(1);
        data.add(2);
        data.add(3);
        data.add(34);
        // Create a Unmodifiable sorted set
        SortedSet<Integer> data2
            = Collections.unmodifiableNavigableSet(data);
        // display
        System.out.println(data);
        // add to data
        data.add(32);
        // display
        System.out.println(data2);
    }
}
```

--------------------------------

### Example Input for Bitwise Operations

Source: https://www.geeksforgeeks.org/java/bitwise-operators-in-java

Sample input values for the bitwise operator program.

```text
Enter first number: 4  
Enter second number: 8
```

--------------------------------

### Demonstrating offerLast() with Strings

Source: https://www.geeksforgeeks.org/java/blockingdeque-offerlast-method-in-java-with-examples

Example showing how offerLast() behaves when inserting strings into a capacity-constrained LinkedBlockingDeque.

```java
// Java Program Demonstrate offerLast()
// method of BlockingDeque

import java.util.concurrent.LinkedBlockingDeque;
import java.util.concurrent.BlockingDeque;
import java.util.*;

public class GFG {
    public static void main(String[] args)
        throws IllegalStateException
    {

        // create object of BlockingDeque
        BlockingDeque<String> BD
            = new LinkedBlockingDeque<String>(4);

        // Add numbers to end of BlockingDeque
        BD.offerLast("abc");
        BD.offerLast("gopu");
        BD.offerLast("geeks");
        BD.offerLast("richik");

        // Cannot be inserted
        BD.offerLast("hii");

        // cannot be inserted hence returns false
        if (!BD.offerLast("hii"))
            System.out.println("The element 'hii' cannot be"
                               + " inserted as capacity is full");

        // before removing print queue
        System.out.println("Blocking Deque: " + BD);
    }
}
```

--------------------------------

### Demonstrating offerLast() with Integers

Source: https://www.geeksforgeeks.org/java/blockingdeque-offerlast-method-in-java-with-examples

Example showing how offerLast() behaves when inserting integers into a capacity-constrained LinkedBlockingDeque.

```java
// Java Program Demonstrate offerLast()
// method of BlockingDeque

import java.util.concurrent.LinkedBlockingDeque;
import java.util.concurrent.BlockingDeque;
import java.util.*;

public class GFG {
    public static void main(String[] args)
        throws IllegalStateException
    {

        // create object of BlockingDeque
        BlockingDeque<Integer> BD
            = new LinkedBlockingDeque<Integer>(4);

        // Add numbers to end of BlockingDeque
        BD.offerLast(7855642);
        BD.offerLast(35658786);
        BD.offerLast(5278367);
        BD.offerLast(74381793);

        // Cannot be inserted
        BD.offerLast(10);

        // cannot be inserted hence returns false
        if (!BD.offerLast(10))
            System.out.println("The element 10 cannot be inserted"
                               + " as capacity is full");

        // before removing print queue
        System.out.println("Blocking Deque: " + BD);
    }
}
```

--------------------------------

### Java Call Stack Execution Example

Source: https://www.geeksforgeeks.org/java/methods-in-java

Demonstrates the order of method execution and the call stack mechanism.

```java
public class CallStackExample {
    public static void D() {
        float d = 40.5f;
        System.out.println("In Method D");
    }
    public static void C() {
        double c = 30.5;
        System.out.println("In Method C");
    }
    public static void B() {
        int b = 20;
        C(); // Calling C
        System.out.println("In Method B");
    }
    public static void A() {
        int a = 10;
        B(); // Calling B
        System.out.println("In Method A");
    }
    public static void main(String[] args) {
        A(); // Start with function A
        D(); // Then call D
    }
}
```

--------------------------------

### Output of Method Overloading Example

Source: https://www.geeksforgeeks.org/java/java-interview-questions

Displays the console output generated by the method overloading demonstration.

```text
multiply() with 2 parameters
20
multiply() with 3 parameters
24
multiply() with 4 parameters
24
```

--------------------------------

### Demonstrate System.err usage

Source: https://www.geeksforgeeks.org/java/java-interview-questions

Example of using System.err.println to output error messages to the console.

```java
import java.io.*;
// Driver Class
class GFG {
    // Main function
    public static void main(String[] args)
    {
        // Printing error
        System.err.println(
            "This is how we throw error with System.err");
    }
}
```

```java
import java.io.*;
```

```java
// Driver Class
```

```java
class GFG {
```

```java
    // Main function
```

```java
    public static void main(String[] args)
```

```java
    {
```

```java
        // Printing error
```

```java
        System.err.println(
```

```java
            "This is how we throw error with System.err");
```

```java
    }
```

```java
}
```

--------------------------------

### Traversing IdentityHashMap

Source: https://www.geeksforgeeks.org/java/identityhashmap-class-java

Basic import statement for starting a traversal example.

```java
import java.util.*;
```

--------------------------------

### Display Output of Generic Example

Source: https://www.geeksforgeeks.org/java/generics-in-java

The expected console output after executing the provided Java generic code.

```text
Sweta
```

--------------------------------

### Demonstrate final keyword usage

Source: https://www.geeksforgeeks.org/java/java-interview-questions

This example illustrates that a variable declared as final cannot be reassigned.

```java
// Java Program to use final
// keyword
import java.io.*;
// Driver Class
class GFG {
    // Main function
    public static void main(String[] args)
    {
        final int x = 100;
        x = 50;
    }
}
```

--------------------------------

### Create and Populate a Hashtable in Java

Source: https://www.geeksforgeeks.org/java/hashtable-in-java

Demonstrates initializing a Hashtable with String keys and Integer values, adding elements, and printing the collection.

```java
import java.util.Hashtable;

public class GFG 
{
    public static void main(String args[]) 
    {
        
      	// Create a Hashtable of String
      	// keys and Integer values
        Hashtable<String, Integer> ht = new Hashtable<>();

        // Adding elements to the Hashtable
        ht.put("One", 1);
        ht.put("Two", 2);
        ht.put("Three", 3);
        
        // Displaying the Hashtable elements
        System.out.println("Hashtable Elements: " + ht);
    }
}
```

--------------------------------

### Creating and Starting a Daemon Thread

Source: https://www.geeksforgeeks.org/java/daemon-thread-java

Demonstrates defining a thread class and marking it as a daemon before starting it. The setDaemon(true) method must be invoked prior to calling start().

```java
class MyDaemonThread extends Thread {
    public void run() {
        System.out.println(getName() + " is running as a daemon thread.");
    }
}

public class GFG {
    public static void main(String[] args) throws InterruptedException {
        MyDaemonThread t1 = new MyDaemonThread();
        t1.setDaemon(true);  // mark as daemon
        t1.setName("Daemon-1");
        t1.start();

        // Give JVM a moment to run daemon thread
        Thread.sleep(100);

        System.out.println("Main thread ends.");
    }
}
```

--------------------------------

### Define and instantiate a Class in Java

Source: https://www.geeksforgeeks.org/java/java-data-types

Shows how to create a blueprint class with a constructor and methods, then instantiate it.

```java
class Car {
    String model;
    int year;

    Car(String model, int year) {
        this.model = model;
        this.year = year;
    }

    void display() {
        System.out.println(model + " " + year);
    }
}

public class Geeks {
    public static void main(String[] args) {
        Car myCar = new Car("Toyota", 2020);
        myCar.display(); 
    }
}
```

```java
class Car {
```

```java
    String model;
```

```java
    int year;
```

```java

```

```java
    Car(String model, int year) {
```

```java
        this.model = model;
```

```java
        this.year = year;
```

```java
    }
```

```java

```

```java
    void display() {
```

```java
        System.out.println(model + " " + year);
```

```java
    }
```

```java
}
```

```java

```

```java
public class Geeks {
```

```java
    public static void main(String[] args) {
```

```java
        Car myCar = new Car("Toyota", 2020);
```

```java
        myCar.display(); 
```

```java
    }
```

```java
}
```

--------------------------------

### User-defined Method Examples

Source: https://www.geeksforgeeks.org/java/methods-in-java

Examples of naming conventions for methods created by the programmer.

```java
sayHello         // user define method created above in the article
Greet() 
setName()
```

--------------------------------

### Demonstrate Method Overriding in Java

Source: https://www.geeksforgeeks.org/java/java-interview-questions

A complete example showing a base class and a subclass overriding the drive method.

```java
// Java Program to demonstrate use of Method Overriding
import java.io.*;
class Vehicle {
    void drive()
    {
        System.out.println("drive() method of base class");
        System.out.println("driving the Car.");
    }
}
class Car extends Vehicle {
    void drive()
    {
        System.out.println(
            "drive() method of derived class");
        System.out.println("Car is driving.");
    }
}
class GFG {
    public static void main(String[] args)
    {
        Car c1 = new Car();
        Vehicle v1 = new Vehicle();
        c1.drive();
        v1.drive();
        Vehicle vehicle = new Car();
        // drive() method of Vehicle class is overridden by
        // Car class drive()
        vehicle.drive();
    }
}
```

```java
// Java Program to demonstrate use of Method Overriding
```

```java
import java.io.*;
```

```java
class Vehicle {
```

```java
    void drive()
```

```java
    {
```

```java
        System.out.println("drive() method of base class");
```

```java
        System.out.println("driving the Car.");
```

```java
    }
```

```java
}
```

```java
class Car extends Vehicle {
```

```java
    void drive()
```

```java
    {
```

```java
        System.out.println(
```

```java
            "drive() method of derived class");
```

```java
        System.out.println("Car is driving.");
```

```java
    }
```

```java
}
```

```java
class GFG {
```

```java
    public static void main(String[] args)
```

```java
    {
```

```java
        Car c1 = new Car();
```

```java
        Vehicle v1 = new Vehicle();
```

```java
        c1.drive();
```

```java
        v1.drive();
```

```java
        Vehicle vehicle = new Car();
```

```java
        // drive() method of Vehicle class is overridden by
```

```java
        // Car class drive()
```

```java
        vehicle.drive();
```

```java
    }
```

```java
}
```

--------------------------------

### Implement Abstraction with TV Remote Example

Source: https://www.geeksforgeeks.org/java/abstraction-in-java-2

Demonstrates basic abstraction using an abstract TV class and a concrete TVRemote implementation.

```java
abstract class TV{
    
    abstract void turnOn();
    abstract void turnOff();
}

// Concrete class implementing the abstract methods
class TVRemote extends TV{
    
    @Override
    void turnOn(){
        
        System.out.println("TV is turned ON.");
    }

    @Override
    void turnOff(){
        
        System.out.println("TV is turned OFF.");
    }
}

// Main class to demonstrate abstraction
public class Geeks{
    
    public static void main(String[] args){
        
        TV remote = new TVRemote();
        remote.turnOn();   
        remote.turnOff();  
    }
}
```

--------------------------------

### Demonstrate IllegalThreadStateException with Multiple start() Calls

Source: https://www.geeksforgeeks.org/java/difference-between-thread-start-and-thread-run-in-java

Calling the start() method more than once on the same thread object triggers an IllegalThreadStateException.

```java
class MyThread extends Thread {

    public void run(){

        System.out.println(
            "Current thread: "
            + Thread.currentThread().getName());
    }
}

public class Geeks{
    
    public static void main(String[] args){
        
        MyThread t = new MyThread();
        t.start();
        t.start(); // Throws exception
    }
}
```

--------------------------------

### Demonstrate offerFirst() with Integers

Source: https://www.geeksforgeeks.org/java/blockingdeque-offerfirst-method-in-java-with-examples

This example shows how to use offerFirst() with a LinkedBlockingDeque of integers and how it handles capacity limits.

```java
// Java Program Demonstrate offerFirst()
// method of BlockingDeque

import java.util.concurrent.LinkedBlockingDeque;
import java.util.concurrent.BlockingDeque;
import java.util.*;

public class GFG {
    public static void main(String[] args)
        throws IllegalStateException
    {

        // create object of BlockingDeque
        BlockingDeque<Integer> BD
            = new LinkedBlockingDeque<Integer>(4);

        // Add numbers to end of BlockingDeque
        BD.offerFirst(7855642);
        BD.offerFirst(35658786);
        BD.offerFirst(5278367);
        BD.offerFirst(74381793);

        // Cannot be inserted
        BD.offerFirst(10);

        // cannot be inserted hence returns false
        if (!BD.offerFirst(10))
            System.out.println("The element 10 cannot be inserted"
                               + " as capacity is full");

        // before removing print queue
        System.out.println("Blocking Deque: " + BD);
    }
}
```

--------------------------------

### Demonstrate ArrayStoreException in Java

Source: https://www.geeksforgeeks.org/java/java-interview-questions

This example shows how an ArrayStoreException occurs when attempting to store an incompatible type in a typed array.

```java
public class GFG {
    public static void main(String args[])
    {
        // Since Double class extends Number class
        // only Double type numbers
        // can be stored in this array
        Number[] a = new Double[2];
        // Trying to store an integer value
        // in this Double type array
        a[0] = new Integer(4);
    }
}
```

--------------------------------

### Demonstrate Object Cloning

Source: https://www.geeksforgeeks.org/java/clone-method-in-java-2

Example showing how to clone an object and verify that the new instance contains identical data.

```java
class GFG implements Cloneable {
    int x, y;

    // Constructor to initialize 
    // object fields
    GFG() {
        x = 10;
        y = 20;
    }

    // Overriding the clone() method
    @Override
    public Object clone() throws CloneNotSupportedException {
        // Returning a clone of the current object
        return super.clone(); 
    }
}

public class Main {
  
    public static void main(String[] args) 
      throws CloneNotSupportedException {
        GFG o1 = new GFG(); 
        
        // Cloning obj1 into obj2
        GFG o2 = (GFG) o1.clone(); 

        System.out.println("o1: " + o1.x + " " + o1.y);
        System.out.println("o2: " + o2.x + " " + o2.y); 
    }
}
```

--------------------------------

### Remove Strings Starting with a Specific Character

Source: https://www.geeksforgeeks.org/java/arraylist-removeif-method-in-java

Uses a lambda expression to filter out strings from an ArrayList based on their starting character.

```java
import java.util.ArrayList;

public class GFG {
    public static void main(String[] args) {

        // Creating an ArrayList of student names
        ArrayList<String> s = new ArrayList<>();

        // Adding student names to the ArrayList
        s.add("Sweta");
        s.add("Gudly");
        s.add("Sohan");
        s.add("Amiya");
        s.add("Ram");

        // Using removeIf() method to 
        // remove names starting with 'S'
        s.removeIf(name -> name.startsWith("S"));

        System.out.println("Students whose names do not start with S:");
        System.out.println(s);
    }
}
```

--------------------------------

### Create and Populate a Map in Java

Source: https://www.geeksforgeeks.org/java/map-interface-in-java

Demonstrates initializing a HashMap and adding key-value pairs using the put method.

```java
import java.util.HashMap;
import java.util.Map;

public class Geeks{
    
    public static void main(String[] args){
        
        // Create a Map using HashMap
        Map<String, Integer> m = new HashMap<>();

        // Adding key-value pairs to the map
        m.put("Geek1", 1);
        m.put("Geek2", 2);
        m.put("Geek3", 3);

        System.out.println("Map elements: " + m);
    }
}
```

--------------------------------

### Create a Type-Safe NavigableSet of Strings Example 2

Source: https://www.geeksforgeeks.org/java/java-collections-checkednavigableset-method-with-examples

An alternative example showing the creation and printing of a type-safe String NavigableSet.

```java
import java.util.*;

public class GFG {

    public static void main(String[] args)
    {
        // create a set of string type
        NavigableSet<String> data = new TreeSet<>();

        // Insert the values into the set
        data.add("java");
        data.add("php/jsp");
        data.add("python");
        data.add("R");

        // type safe view of the set
        System.out.println(Collections.checkedNavigableSet(
            data, String.class));
    }
}
```

--------------------------------

### Check File Existence and Properties in Java

Source: https://www.geeksforgeeks.org/java/file-class-in-java

Demonstrates how to instantiate a File object and retrieve metadata such as path, existence, and permissions.

```java
import java.io.File;

// Displaying file property
class CheckFileExist {

    public static void main(String[] args){

        // Accept file name or directory name through
        // command line args
        String fname = args[0];

        // pass the filename or directory name to File
        // object
        File f = new File(fname);

        // apply File class methods on File object
        System.out.println("File name :" + f.getName());
        System.out.println("Path: " + f.getPath());
        System.out.println("Absolute path:"
                           + f.getAbsolutePath());
        System.out.println("Parent:" + f.getParent());
        System.out.println("Exists :" + f.exists());

        if (f.exists()) {
            System.out.println("Is writable:"
                               + f.canWrite());
            System.out.println("Is readable" + f.canRead());
            System.out.println("Is a directory:"
                               + f.isDirectory());
            System.out.println("File Size in bytes "
                               + f.length());
        }
    }
}
```

--------------------------------

### Create a Java String using the new keyword

Source: https://www.geeksforgeeks.org/java/strings-in-java

Demonstrates basic string instantiation using the String constructor.

```java
public class Geeks {

    // Main Function
    public static void main(String args[])
    {

        // creating Java string using a new keyword
        String str = new String("Geeks");

        System.out.println(str);
    }
}
```

--------------------------------

### Demonstrate System.out usage

Source: https://www.geeksforgeeks.org/java/java-interview-questions

Basic implementation of System.out.println to write data to the console.

```java
import java.io.*;
// Driver Class
class GFG {
    // Main Function
    public static void main(String[] args)
    {
        // Use of System.out
        System.out.println("");
    }
}
```

```java
import java.io.*;
```

```java
// Driver Class
```

```java
class GFG {
```

```java
    // Main Function
```

```java
    public static void main(String[] args)
```

```java
    {
```

```java
        // Use of System.out
```

```java
        System.out.println("");
```

```java
    }
```

```java
}
```

--------------------------------

### CopyOnWriteArrayList Constructors

Source: https://www.geeksforgeeks.org/java/copyonwritearraylist-in-java

Examples of different ways to instantiate a CopyOnWriteArrayList.

```java
CopyOnWriteArrayList<String> c = new CopyOnWriteArrayList<>();
```

```java
CopyOnWriteArrayList<String> c = new CopyOnWriteArrayList<>(collection);
```

```java
CopyOnWriteArrayList<String> c = new CopyOnWriteArrayList<>(array);
```

--------------------------------

### Define and Call an Instance Method in Java

Source: https://www.geeksforgeeks.org/java/instance-methods-in-java

Demonstrates creating a class with an instance method and invoking it through an object instance.

```java
class Person {
    String name = "Alice";

    // Instance method
    void greet()
    {
        System.out.println("Hello, " + name + "!");
    }

    public static void main(String[] args)
    {
        Person p = new Person();
        p.greet(); // Calling instance method
    }
}
```

--------------------------------

### Display Immutability output

Source: https://www.geeksforgeeks.org/java/strings-in-java

Standard output result for the immutability example.

```text
Hello
```

--------------------------------

### Connect to MySQL Database using JDBC

Source: https://www.geeksforgeeks.org/java/establishing-jdbc-connection-in-java

Demonstrates loading the driver, establishing a connection, executing a query, and closing resources.

```java
import java.sql.*;

class Geeks {
    public static void main(String[] args) throws Exception {
        String url = "jdbc:mysql://localhost:3306/database_name"; // Database details
        String username = "rootgfg"; // MySQL credentials
        String password = "gfg123";
        String query = "select * from students"; // Query to be run

        // Load and register the driver
        Class.forName("com.mysql.cj.jdbc.Driver");

        // Establish connection
        Connection con = DriverManager.getConnection(url, username, password);
        System.out.println("Connection Established successfully");

        // Create a statement
        Statement st = con.createStatement();

        // Execute the query
        ResultSet rs = st.executeQuery(query);

        // Process the results
        while (rs.next()) {
            String name = rs.getString("name"); // Retrieve name from db
            System.out.println(name); // Print result on console
        }

        // Close the statement and connection
        st.close();
        con.close();
        System.out.println("Connection Closed....");
    }
}
```

--------------------------------

### Individual Code Fragments

Source: https://www.geeksforgeeks.org/java/java-comparator-interface

Individual components of the Student sorting example.

```java
import java.util.*;
```

```java
class Student {
```

```java
    int id;
```

```java
    String name;
```

```java
    Student(int id, String name) {
        this.id = id;
        this.name = name;
    }
```

```java
}
```

```java
public class ComparatorExample {
    public static void main(String[] args) {

        ArrayList<Student> list = new ArrayList<>();
        list.add(new Student(2, "Rahul"));
        list.add(new Student(1, "Amit"));

        Collections.sort(list, (s1, s2) -> Integer.compare(s1.id, s2.id));

        for (Student s : list) {
            System.out.println(s.id + " " + s.name);
        }
    }
}
```

--------------------------------

### Defining an Enum

Source: https://www.geeksforgeeks.org/java/enumset-class-java

Example of an enum definition used for EnumSet operations.

```java
enum e { CODE, LEARN, CONTRIBUTE, QUIZ, MCQ };
```

--------------------------------

### Define and Initialize a Java Class

Source: https://www.geeksforgeeks.org/java/classes-objects-java

Defines a Product class with instance variables and a constructor, demonstrating object instantiation and state access.

```java
class Product {

    String name;
    float price;

    // Constructor to initialize object state
    public Product(String name, float price) {
        this.name = name;
        this.price = price;
    }

    // Setter methods (optional)
    public void setName(String name) {
        this.name = name;
    }

    public void setPrice(float price) {
        this.price = price;
    }

    // Getter methods
    public String getName() {
        return name;
    }

    public float getPrice() {
        return price;
    }
}

public class Main {
    public static void main(String[] args) {

        Product p1 = new Product("Visual Studio", 0.0f);
        Product p2 = new Product("IntelliJ IDEA", 4999.0f);

        System.out.println(p1.getName() + " - " + p1.getPrice());
        System.out.println(p2.getName() + " - " + p2.getPrice());
    }
}
```

--------------------------------

### Basic Object Creation with newInstance()

Source: https://www.geeksforgeeks.org/java/constructor-newinstance-method-in-java-with-examples

Demonstrates creating an object using a no-argument constructor via reflection.

```java
import java.lang.reflect.Constructor;
class Test{
    public Test(){
        System.out.println("Object created");
    }
}
public class GFG {
    public static void main(String[] args) throws Exception {
        Constructor<Test> constructor = Test.class.getConstructor();
        constructor.newInstance();
    }
}
```

--------------------------------

### Fragmented Code Example

Source: https://www.geeksforgeeks.org/java/arraylist-retainall-method-in-java

A fragmented representation of the ArrayList retainAll() implementation.

```java
import java.util.*;
```

```java

```

```java
public class GFG {
```

```java

```

```java
    public static void main(String[] args) {
```

```java

```

```java
        ArrayList<String> classA = new ArrayList<>();
```

```java

```

```java
        classA.add("Amit");
```

```java
        classA.add("Rahul");
```

```java
        classA.add("Priya");
```

```java
        classA.add("Neha");
```

```java

```

```java
        ArrayList<String> classB = new ArrayList<>();
```

```java

```

```java
        classB.add("Rahul");
```

```java
        classB.add("Priya");
```

```java
        classB.add("Riya");
```

```java

```

```java
        classA.retainAll(classB);
```

```java

```

```java
        System.out.println(classA);
```

```java
    }
```

```java
}
```

--------------------------------

### ArrayBlockingQueue Implementation Example

Source: https://www.geeksforgeeks.org/java/arrayblockingqueue-class-in-java

Demonstrates initializing an ArrayBlockingQueue, adding elements using offer(), and iterating through the queue.

```java
import java.util.*;
import java.util.concurrent.ArrayBlockingQueue;

public class Geeks {
    public static void main(String[] args)
    {
        // Define capacity of ArrayBlockingQueue
        int c = 5;

        ArrayBlockingQueue<String> q = new ArrayBlockingQueue<String>(c);

        q.offer("Java");
        q.offer("C++");
        q.offer("Python");
        q.offer("Js");

        System.out.println("ArrayBlockingQueue is: " + q);

        Iterator i = q.iterator();

        System.out.println("The iterator values:");
        while (i.hasNext()) {
            System.out.print(i.next() + " ");
        }
    }
}
```

--------------------------------

### Declare and Initialize Strings in Java

Source: https://www.geeksforgeeks.org/java/strings-in-java

Demonstrates the difference between creating strings using literals and the new keyword.

```java
class Geeks
 {
    public static void main(String args[])
    {
        
      	// Declaring Strings using String literals
        String s1 = "TAT";
        String s2 = "TAT";

        // Declaring Strings using new keyword
        String s3 = new String("TAT");
        String s4 = new String("TAT");

        // Printing all the Strings
        System.out.println(s1);
        System.out.println(s2);
        System.out.println(s3);
        System.out.println(s4);
    }
 }
```

--------------------------------

### Java Interface Output

Source: https://www.geeksforgeeks.org/java/differences-between-interface-and-class-in-java

The console output resulting from the interface implementation example.

```text
Geek
10
```

--------------------------------

### Establish Database Connection in Java

Source: https://www.geeksforgeeks.org/java/how-to-use-callable-statement-in-java-to-call-stored-procedure

Initializes the MySQL driver and establishes a connection to the database.

```java
import java.sql.*;
public class JavaApplication1 {
   public static void main(String[] args) throws Exception
   {
       Class.forName("com.mysql.jdbc.Driver");
       Connection con=DriverManager.getConnection("jdbc:mysql://localhost/root","geek","geek");  
   }  
}
```

--------------------------------

### Collections.min() with Comparator

Source: https://www.geeksforgeeks.org/java/collections-min-method-in-java-with-examples

Initial setup for using the min() method with a custom comparator.

```java
// Java program to demonstrate
// min() method
// for Integer

import java.util.*;

public class GFG1 {
    public static void main(String[] argv) throws Exception
    {
        try {

            // create link list object
            List<Integer> list = new LinkedList<Integer>();

            // populate the list
            list.add(10);
            list.add(20);
            list.add(30);
            list.add(40);
```
Tokens:
Raw