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());
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
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 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;
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
