Online-Academy
Look, Read, Understand, Apply

Some Program Codes 

Program 1:
 //Do math according to user choice
import java.util.*;
class basic_num{
    public static void main(String[] args){
        //relational operators: >, >=, <=, ==,<, !=
        int x=300_200,y=5;
        System.out.print("First: "+args[0]);
        Scanner s = new Scanner(System.in);
        String ch = s.next();
        System.out.print("ch: "+ch);
        switch(ch){
            case "+":System.out.print(x+y);
            break;
            case "*":System.out.print(x+y);
            break;
        }
    }
}



Program 2:
 //box class with length, breadth,height, area, volume
//methods to calculate area, volume
/*
 * box --> l, b, h, area, volume
 */
class box_a{
    private int l,b,h;
    //private int b;
    //private int h; //member variables
    public int area; 
    public int volume; 
    public void set(int l,int b, int h){
        this.l = l;
        this.b = b;
        this.h = h;
    }
    public int getArea(){
        area = l * b;
        return area;
    }
    public int getVolume(){
        volume = l * b * h;
        return volume; 
    }
}
class box_demo_i{
    public static void main(String[] para){
        box_a b1 = new box_a();
        b1.set(2,3,4);//l = 2, b = 3, h = 4;
        System.out.println("Area: "+b1.getArea());
        System.out.println("Volume: "+b1.getVolume());
        box_a b2 = new box_a();
        b2.set(4,5,7);
        b1.h = 3;
        System.out.println("Area: "+b2.area);
        System.out.println("Volume: "+b2.volume);
    }
}

Program 3:

//using Command line argument
class command_args{
    public static void main(String[] aa){
        System.out.println("Elements count: "+aa.length);
        int x = Integer.parseInt(aa[0]);
        int y = Integer.parseInt(aa[1]);
        int sum = x + y;
        if(x % 2 == 0 ){
            System.out.println(x+ ": Even");
        }else{
            System.out.println(x+ ": Odd");
        }
        System.out.println("Sum: "+sum);
        for(int i=0;i<aa.length;i++){
            System.out.println(i+": "+aa[i]);
        }
    }
}

Program 4:

//Performing Dynamic Polymorphism
class person{
    int id;
    String name;
    public person(int id,String name){
        this.id = id;
        this.name = name;
    }
    public void show(){
        System.out.println("ID: "+id+"\nName: "+name);
    }
}
class student extends person{
    String school;
    public student(int age, String name,String school){
        super(age, name);
        this.school = school; 
    }
    public void show(){//method overriding
        //based class method is redefined by derived class. 
        super.show();
        System.out.println("School: "+school);
    }
}
class dyna_ploy_demo{
    public static void main(String[] oo){
        person p = new person(1,"Dinesh");
        p.show();
        p = new student(2,"Sheetal","AAMV");
        //based class object can take reference of child class. 
        p.show();//student has show, person also has show method. 
    }
}


Program 5:

/*Dynamic Polymorphism in Java (also known as runtime polymorphism) is a core concept of object-oriented programming where method calls are resolved at runtime rather than compile-time.
It refers to the ability of a program to decide which method implementation to execute at runtime, rather than at compile time. 
*/

/*bubble sorting: sorting list of data in order (ascending or descending)*/
class fib_series{
    public static void main(String[] aa){
        int[] arr = {33,22,1,4,6,7,5,99,10};
        int i,j,temp,n = arr.length;
        for(i=0;i<n;i++){
            for(j=0;j<n;j++){
                if(arr[j+1]<arr[j]){
                    temp = arr[j+1];
                    arr[j+1] = arr[j];
                    arr[j] = temp;
                }
                System.out.print(" "+arr[j]);
            }
            System.out.println();
        }
        for(i=0;i<n;i++){
            System.out.print(" "+arr[i]);
        }
    }
}
/*
 * a = 4, b = 5; c = a, a = b, b = c
 * c = 4, a = 5 ; b = 4
 */


Program 6:

 interface abc{
    void show();
}
interface xyz{
    void sayHello();
}
class C1 implements abc,xyz{
    public void show(){
        System.out.println("Hello from Interface");
    }
    public void sayHello(){
        System.out.println("Hello said");
    }
}
class InterfaceDemo{
    public static void main(String[] arr){
        C1 c = new C1();
        c.show();
        c.sayHello();
        abc x = new C1();
        x.show();
        //x.sayHello();
        xyz z = new C1();
        z.sayHello();
    }
}

Program 7:

/* 
In Java, an interface is a reference type, similar to a class, that can contain only:
- Abstract methods (implicitly public and abstract)
- Default methods (with a body, using default)
- Static methods
- Constant fields (public static final)

Purpose of Interfaces
- Define a contract that implementing classes must follow.
- Support multiple inheritance (Java doesn't allow multiple class inheritance, but a class can implement multiple interfaces).
- Enable polymorphism and abstraction.

AFTER JAVA 8, methods in interface can have definition
interface MyInterface {
    default void show() {
        System.out.println("Default implementation");
    }
}

interface MyInterface {
    static void display() {
        System.out.println("Static method in interface");
    }
}

interface MyInterface {
    int VALUE = 10; // implicitly public, static, final
}

When to Use Interfaces
When you need a common functionality contract for unrelated classes.*/

Program 8:

//Calculating value of a number powered by some number.
class power{
    public static void main(String[] para){
        int x=3,y =5;
        int p = x;
        for(int i=2;i<=y;i++){
            p = p * x;             
        }
        System.out.print("Power of "+x+" is: "+p);
    }
}