Java basics - part 1

This is the very beginning of a JAVA programming series, which covers basics, important points regarding sequence, selection, iteration, std in, std out, and lot more.

This post contains some important thins regarding Java language, and most of them are coming as learning outcomes from "Hackerrank" Java problem solving.

Std Input

import scanner class

import java.util.Scanner;

 

Then use like below 

Scanner scan = new Scanner(System.in);

int i = scan.nextInt();

String s = scan.nextLine();

 

do{
String st1=scan.nextLine();
System.out.println(count + " " + st1);
count += 1;
}while(scan.hasNext());

while(scan.hasNext()){
// String st1=scan.nextLine();
st1 = scan.nextLine();
System.out.println(count + " " + st1);
count += 1;
} 

 

scan.close();

 

Std Output

Use standard output to send to terminal

 

System.out.println("String val: " + stringVariable );

System.out.println("Double val: " + Double.toString(doubleVariable) );

System.out.println("Integer val: " + Integer.toString(integerValue) );

 

 

If - else if - else, Switch, shorthand if  

// if - else if - else

if(intVar > 100){

    System.out.println(">100");

}

else if(intVar >= 80){

    System.out.println(">=80");

}

else{

    System.out.println("<80");

}

 

// shorthand

resultVar = (intVar > 100) ? ">100" : ( (intVar >= 80) ? ">=80" : "<80" );

System.out.println(resultVar);

 

// switch - case

switch(someInteger){

    case 1:

        System.out.println("equals 1");

        break;

    case 2:

        System.out.println("equals 2");

        break;

    case 5:

        System.out.println("equals 5");

        break;

    default:

        System.out.println("default value");

}

 

formatting output with printf

// 15 chars left is a string, right aligning integer with 3 digits

System.out.printf("%-15s%03d\n", stringVar, intVar);

 

Type casting

// double to int 

int var1 = (int)( Math.pow(2, c)*b ); 

int var1 = new Double(Math.pow(2, c)*b).intValue() 

 

// int to String

String var3 = Integer.toString(intValue);

String var4 = String.valueOf(intValue);

 

// String to char array

char[] arr = stringVar.toCharArray(); 

 

Static Initializer

public class Javaclass{

    static boolean flag = false;
    static int B=0;
 

    // this part executes before the main method
    static {
        System.out.print("Inside static initializer");
     Scanner sc = new Scanner(System.in);
    B = sc.nextInt();
  flag = true;

    }

 

    public static void main(String[] args){

        if(flag){

            // do something

        }

    } 

} 

 

Currency formatting

create a NumberFormat 

NumberFormat cf 

 

If currency for your locale is available, get it 

NumberFormat nf = NumberFormat.getCurrencyInstance(Locale.US) 

 

or create a new locale

Locale my_locale = new Locale("en", "LK"); // LK for Sri Lanka, extended from "en"

NumberFormat nf = NumberFormat.getCurrencyInstance(my_locale);

 

Then use the NumberFormat to print double value as a currency

double doubleValue = 20.3; // 0.22, 40, 2,45

System.out.print( nf.format(doubleValue) );

 

Probable Prime

BigInteger bigIntInstance = new BigInteger(n);

boolean isPrime = bigIntInstance.isProbablePrime(1);

 

Let's meet with the next post

Thanks for the reading