34_Enums.java

// Enums in Java

import java.util.*;

class Solution {
    public static void main(String args[]){
        Scanner sc = new Scanner(System.in);
        
        ReqStatus r = ReqStatus.PENDING;
        System.out.println(r);

        switch (r) {
            case PENDING:
                System.out.println("0");
                break;
            case RUNNING: 
                System.out.println("1");
                break;
            default: 
                System.out.println("def");
                break;
        }

        // Enums can be traversed using the values method.
        for(ReqStatus s: ReqStatus.values()){
            System.out.println(s);
        }

        // Values() : Returns an iterable list of all the constants in the enum
        System.out.println(ReqStatus.values());

        // Enum: 
        // Group of constants. 
        // all the user defined enums class are internally inheriting the 
        // Enum class(Java.lang.enum) from library(Java.lang) which includes default methods like 
        // values(), getClass(), etc.
        // We cannot use new keyword with enum because it has private constructor
        // only.

    }
}

// All the enum member variable are final(const), static by default(implicitly)

// Syntax: 
// enum {
//        Your Constant goes here(seprated by comma);
// }

enum ReqStatus{
    PENDING, RUNNING, REJECTED, WAITING, RESOLVED;
}

class Solution1 {

    // Create enum inside Solution class.
    public enum Week{MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY}
    public static void main(String args[]){
        Scanner sc = new Scanner(System.in);
        
        for(Week wk: Week.values()) System.out.println(wk);
    }
}


// ------------------------------------------------------------------------

enum Laptops {

    // Each Constant of enum acts as an instance of the class.
    MAC(2500), XPS(1200, 2), HP(300), SURFACE(1800, 5), THINKPAD(1600);

    int p;

    // All the instance of the Laptops can be initialised using constructors only.
    // These constructors are private by default. 
    // So we need not to pass any argument in main.
    Laptops(int price){
        p = price;
    }

    // We can access each instance using methods.
    int displayPrice(){
        return p;
    }

    // Overload constructor to add a multiplier to the price.
    Laptops(int price, int multiplier) {
        p = price * multiplier;
    }

    // Default Constructor
    Laptops(){}

    // Setter Function
    void setPrice(int price, int mul) {
        p = price * mul;
    }
}

class Solution1 {

    // function overloading
    static int add(int a, int b) {
        return a+b;
    }

    static int add(int a) {
        return a + 1;
    }

    static void pr(){
        System.out.println("Print1");
    }
    static void pr(int a){
        System.out.println("Print2");
    }

    // Create enum inside Solution class.
    public enum Week{MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY;}
    public static void main(String args[]){
        Scanner sc = new Scanner(System.in);
        
        // Traverse.
        for(Week wk: Week.values()) System.out.print(wk + " ");
        System.out.println();

        // Ordinal Method: Returns the index of constant.
        Laptops lp = Laptops.HP;
        System.out.println(lp.ordinal()); // Prints 2;

        for(Laptops l: Laptops.values()){
            System.out.print(l.ordinal() + " "); // 0,1,2,3,4,5
        }
        System.out.println();

        for(Laptops l: Laptops.values()){
            System.out.print(l.displayPrice() + " "); // Prints price of each laptop.
            l.setPrice(32, 0); // Sets the price to zero for each constant.
        }
        System.out.println();

        for(Laptops l: Laptops.values()){
            System.out.print(l.displayPrice() + " "); // 0 0 0 0 0
        }

        System.out.println(add(3));
        System.out.println(add(3, 4));

        pr();
        pr(40);
    }


}