1.
Class and Object
class Student {
String name;
int age;
void display() {
System.out.println("Name: " + name + ", Age: " + age);
}
public static void main(String[] args) {
Student s1 = new Student();
s1.name = "John";
s1.age = 20;
s1.display();
}
}
Output:
Name: John, Age: 20
2. Constructor
class Car {
String model;
Car(String m) {
model = m;
}
void display() {
System.out.println("Car Model: " + model);
}
public static void main(String[] args) {
Car car1 = new Car("Toyota");
car1.display();
}
}
Output:
Car Model: Toyota
3. Destructor (Finalizer)
class FinalizerDemo {
protected void finalize() {
System.out.println("Object is garbage collected");
}
public static void main(String[] args) {
FinalizerDemo obj = new FinalizerDemo();
obj = null;
System.gc();
}
}
Output:
Object is garbage collected (May vary depending on GC execution)
4. Single Inheritance
class Animal {
void sound() {
System.out.println("Animals make sound");
}
}
class Dog extends Animal {
void bark() {
System.out.println("Dog barks");
}
public static void main(String[] args) {
Dog d = new Dog();
d.sound();
d.bark();
}
}
Output:
Animals make sound
Dog barks
5. Multilevel Inheritance
class Animal {
void eat() {
System.out.println("Animals eat food");
}
}
class Mammal extends Animal {
void walk() {
System.out.println("Mammals walk");
}
}
class Human extends Mammal {
void speak() {
System.out.println("Humans speak");
}
public static void main(String[] args) {
Human h = new Human();
h.eat();
h.walk();
h.speak();
}
}
Output:
Animals eat food
Mammals walk
Humans speak
6. Hierarchical Inheritance
class Animal {
void eat() {
System.out.println("Animals eat food");
}
}
class Dog extends Animal {
void bark() {
System.out.println("Dog barks");
}
}
class Cat extends Animal {
void meow() {
System.out.println("Cat meows");
}
public static void main(String[] args) {
Dog d = new Dog();
d.eat();
d.bark();
Cat c = new Cat();
c.eat();
c.meow();
}
}
Output:
Animals eat food
Dog barks
Animals eat food
Cat meows
7. Method Overloading
class MathOperations {
int add(int a, int b) {
return a + b;
}
double add(double a, double b) {
return a + b;
}
public static void main(String[] args) {
MathOperations obj = new MathOperations();
System.out.println("Sum (int): " + obj.add(5, 10));
System.out.println("Sum (double): " + obj.add(5.5, 10.5));
}
}
Output:
Sum (int): 15
Sum (double): 16.0
8. Method Overriding
class Parent {
void show() {
System.out.println("Parent's show method");
}
}
class Child extends Parent {
void show() {
System.out.println("Child's show method");
}
public static void main(String[] args) {
Parent p = new Child();
p.show();
}
}
Output:
Child's show method
9. Abstract Class
abstract class Shape {
abstract void draw();
}
class Circle extends Shape {
void draw() {
System.out.println("Drawing Circle");
}
public static void main(String[] args) {
Shape s = new Circle();
s.draw();
}
}
Output:
Drawing Circle
10. Interface
interface Animal {
void makeSound();
}
class Dog implements Animal {
public void makeSound() {
System.out.println("Dog barks");
}
public static void main(String[] args) {
Dog d = new Dog();
d.makeSound();
}
}
Output:
Dog barks
11. Static Keyword
class StaticExample {
static int count = 0;
StaticExample() {
count++;
System.out.println("Object count: " + count);
}
public static void main(String[] args) {
new StaticExample();
new StaticExample();
new StaticExample();
}
}
Output:
Object count: 1
Object count: 2
Object count: 3
12. Encapsulation
class Person {
private String name;
public void setName(String n) {
name = n;
}
public String getName() {
return name;
}
public static void main(String[] args) {
Person p = new Person();
p.setName("John");
System.out.println("Name: " + p.getName());
}
}
Output:
Name: John
13. Polymorphism (Runtime)
class Animal {
void makeSound() {
System.out.println("Animal makes a sound");
}
}
class Dog extends Animal {
void makeSound() {
System.out.println("Dog barks");
}
public static void main(String[] args) {
Animal a = new Dog();
a.makeSound();
}
}
Output:
Dog barks
14. File Handling
import java.io.FileWriter;
import java.io.IOException;
class FileDemo {
public static void main(String[] args) {
try {
FileWriter writer = new FileWriter("output.txt");
writer.write("Hello, File Handling in Java!");
writer.close();
System.out.println("File written successfully");
} catch (IOException e) {
System.out.println("An error occurred");
}
}
}
Output:
File written successfully (A file named output.txt will be created)
15. Exception Handling
class ExceptionDemo {
public static void main(String[] args) {
try {
int result = 10 / 0;
} catch (ArithmeticException e) {
System.out.println("Cannot divide by zero");
}
}
}
Output:
Cannot divide by zero
