Coffee break #117. Java Enum - enumeration with specific examples. While Loop in Java: Syntax and Uses

Java Enum - enumeration with examples in Java

Source: FreeCodeCamp An enumeration (enumeration or enum for short) in Java is a special data type that contains a set of predefined constants. Typically, enum is used when working with values ​​that do not need to be changed, such as days of the week, seasons, colors, and so on. In this article, we will see how to create an enum and how to assign its value to other variables. We will also learn how to use an enum in a switch statement or loop through its values.

How to create an Enum in Java

To create an enum we use the enum keyword . This is similar to how you create a class using the class keyword . Here's an example:

enum Colors {
  RED,
  BLUE,
  YELLOW,
  GREEN
}

In this code, we have created an enum called Colors . You may notice that all enum values ​​here are written in upper case - but this is just a general convention. If the values ​​are written in lowercase, there will be no error. Each value in enum is separated by a comma. Next we're going to create a new variable and assign it one of the values ​​of our enum .

enum Colors {
  RED,
  BLUE,
  YELLOW,
  GREEN
}

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

    Colors red = Colors.RED;

    System.out.println(red);
    // RED
  }
}

This is similar to initializing any other variable. Here in the code we have initialized the Colors variable and assigned it one of the enum values ​​using the dot syntax: Colors red = Colors.RED; . Note that we can create our enum inside the Main class and the code will still work:

public class Main {
  enum Colors {
  RED,
  BLUE,
  YELLOW,
  GREEN
}
  public static void main(String[] args) {

    Colors red = Colors.RED;

    System.out.println(red);
  }
}

If we want to get the ordinal number of any of the values, we will have to use the ordinal() method . Here's another example:

enum Colors {
  RED,
  BLUE,
  YELLOW,
  GREEN
}

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

    Colors red = Colors.RED;

    System.out.println(red.ordinal());
    // 0
  }
}

red.ordinal() from the above code returns 0.

How to use Enum in a Switch statement

Now we will learn how we can use enum in a switch statement :

public class Main {
      enum Colors {
      RED,
      BLUE,
      YELLOW,
      GREEN
  }
  public static void main(String[] args) {

    Colors myColor = Colors.YELLOW;

    switch(myColor) {
      case RED:
        System.out.println("The color is red");
        break;
      case BLUE:
         System.out.println("The color is blue");
        break;
      case YELLOW:
        System.out.println("The color is yellow");
        break;
      case GREEN:
        System.out.println("The color is green");
        break;
    }
  }
}

This is a very simple example of how we can use enum in a switch statement . We can output "The color is yellow" to the console because this is the only case that matches the condition of the switch statement .

How to loop through enum values

For enum, Java has a values() method that returns an array of enum values . We're going to use a foreach loop to iterate through and print the values ​​of our enum . You can do it like this:

enum Colors {
  RED,
  BLUE,
  YELLOW,
  GREEN
}

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

      for (Colors allColors : Colors.values()) {
      System.out.println(allColors);

      /*
      RED
      BLUE
      YELLOW
      GREEN
      */
    }

  }
}

Conclusion

In this article, we learned what an enum is in Java, how to create one, and how to assign its values ​​to other variables. We also saw how to use the enum type with a switch statement , and how we can loop through enum values . Happy coding!

While Loop in Java: Syntax and Uses

Source: Dev.to Today we will understand the concept and syntax of a while loop in Java and also look at how to use this loop to iterate through an array.

While Loop Concept

The while loop is one of the basic loop types in Java and can be used for several purposes in a program. Like the for loop , the while loop can be used to perform operations based on a condition. In a while loop , the counter does not always turn on. The number of iterations of the while loop depends on how often the loop condition returns true . Initialization in a while loop can be optional in most cases, unlike in a for loop . Sometimes the while loop is not always executed in a loop. Let's take a concrete example:

System.out.println("You Input a wrong number");
       int i = input.nextInt();
       while(i==1||i==2||i==3||i==4){
           System.out.println("inside the while loop block");
       }
       //if the user chooses any number different from 1,2,3 and 4.
       System.out.println("outside the while loop block")

Here the code uses a while loop to validate user input based on some conditions, so it repeats only once.

While loop syntax

while(condition){
//Statements
}

The while loop condition takes an argument that returns the boolean value true or false . When true the code in the while loop is executed, but when false the loop ends.

Flow of each while loop

The while loop has an accepted flow: initialization > condition > statements execution. The first stage is the initialization stage. It can be accomplished by declaring a variable and also initializing it. The second stage is the condition stage, this stage must return true or false . If it returns true , the statement in the while loop is executed, but if it returns false , the loop ends.

Using a while loop as a counter

Like the for loop , the while loop can also be used as a counter. The program below uses a while loop to iterate from 2 to 20. This is to print even numbers.

int j = 2;
       while(j <=20){
           System.out.println(j);
           j+=2;
       }

As you can see, in the program, j is initialized to 2, the condition is tested if j is less than or equal to 20. If it returns true , the statement is executed, but if it returns false , the while loop ends.

A while loop can be used to iterate through an array

int[] age = {20, 30, 40, 40, 90};
        int i = 0;
        while (i < age.length)
        {
            System.out.println(age[i]);
            i++;
        }

In this code, we have an age array and a while loop is used to iterate through the array and print out each element in the array. To check the total number of elements in an array, age.length is used , in the above program i serves as an index.

Break statement in a while loop

The break statement can also be used in a while loop , just like a for loop :

int i = 1;
        while (true)
        {
            System.out.println(i);
            if (i == 20)
            {
                break;
            }
            i++;
        }

In the above program, the break statement was used to stop the program from executing indefinitely. While(true) means that the program will always return true .

The while loop can be used to validate user input

System.out.println("Select an option\n"+
         "1.Add Users\n"+
         "2.Delete Users");
         int x = input.nextInt();
         while(x==1||x==2){
         //Do something
         }
System.out.println("You Input a wrong number");

In the above program, a while loop is used to check the user's input and ensure that the user selects either 1 or 2. If the user selects a different number, then System.out.println("You Input a wrong number"); .

Conditional statement with while loop

int i = 0;
        while(i<10){

            i++;
            if(i==5){
                continue;
            }             System.out.println(i);
        }

The conditional statement can also be used in a while loop to skip a specific iteration. In the above program, if statement is used to check i==5 , if it returns true then that particular iteration will be skipped.

while loop design

Let's create a guessing game using a while loop .

import java.util.*;

public class Main
{
    static Scanner input = new Scanner(System.in);

    static boolean hasWon;
    static int count;
    static int guess;

    public static void main (String[] args)
    {
        System.out.println("Welcome to guess world");

        System.out.println("Do you want to start the game? ");
        System.out.println("1.Yes\n" +
                           "2.No");
        int option= input.nextInt();
        int guessNumber = (int) Math.floor(Math.random() * 10 + 1);
        if (!( option == 2 ))
        {
            System.out.println("Welcome, choose a guess between 1 and 10\n" +
                               "you have only ten trials");


            while (count <= 10)
            {
                int userGuess = input.nextInt();
                if (userGuess == guessNumber)
                {
                    hasWon = true;
                    System.out.println("Congratulation, you guessed right at " + count + " count");

                    count++;
                    break;
                }
                else if (userGuess < guessNumber)
                {
                    hasWon = false;
                    System.out.println("Oops, you guessed a lower number, try an higher one");
                    count++;
                }
                else if (userGuess > guessNumber)
                {
                    System.out.println("Oops, you guessed an high number, try an lower one");
                    hasWon = false;
                }
            }
            if (hasWon == false)
            {
                System.out.println("You trials exceeds 10");
            }
        }


    }
}

In this program, we create a number guessing game using a while loop . The player has only 10 attempts. Once the number of times he has played the game exceeds 10, the game ends. If the player guesses the correct number, a congratulations message is displayed on the console.

Conclusion

The while loop may seem complicated, but it's not that difficult to master. It is also the second most commonly used loop in Java and can be used for a variety of purposes.