Notes2.java

/*
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
TOPICS :: Arrays, Constants('final'), Math methods, NumberFormat, Reading Input, trim.
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
*/

// Exceptions are Java's way to report errors

import java.util.Arrays;
import java.util.Scanner;
import java.text.NumberFormat;

public class Notes2 {

    public static void main(String[] args) {

        //Array in Java are of fixed lengths.
        int[] sampleArray = new int[10]; //size : 10
        sampleArray[0] = 2;
        sampleArray[1] = 4;
        System.out.println(Arrays.toString(sampleArray)); //Output > [2, 4, 0, 0, 0, 0, 0, 0, 0, 0]
        /*
            Methods of Array: sort(), toString(), ...
        */

        int[] iniArray = {2, 3, 1, 5, 4};
        System.out.println(iniArray.length); //Output > 5

        //Multidimension Arrays
        int[][] multiArr = new int[2][3];
        int[][] iniMultiArr = {{1, 2, 3}, {4, 5, 6}};
        multiArr[0][0] = 1;
        System.out.println(Arrays.toString(multiArr)); //Output > [[I@4dc63996, [I@d716361]  :bcs one index is an array
        System.out.println(Arrays.deepToString(multiArr)); //Output > [[1, 0, 0], [0, 0, 0]]

        //Constants in Java are named in allCapital format.
        //to declare a constant(which cannot be changed in the program) we use 'final' keyword before declaration
        final float PI = 3.14F;

        //operations: same as in C/C++
        int s = 10 / 3; //s=3
        double s2 = (double)10 / (double)3 ; //s2=3.3333333333333335 //type casting

        short sh = 1;
        int y = sh + 2; //Implicit typecasting > byte -> short -> int -> long -> float -> double

        //note the Capital 'S' in 'String' keyword
        String intStr = "123";
        System.out.println(Integer.parseInt(intStr)); //Output > 123

        double s3 = Double.parseDouble("1.1") + 2;
        System.out.println(s3); //Output > 3.1


        //Math class operations: max, min, floor, ceil, round, abs, sqrt
        //Math.round: float -> int , double -> long
        System.out.println(Math.round(1.3F)); // Ouput > 1
        System.out.println(Math.ceil(2.5F)); // Output > 3.0 //Note it produces a double value & not int.
        System.out.println(Math.random()); // Ouput > a random flaot value between 0 - 1

        //We cannot create an instance of an abstract class.
        //NumberFormat is an abstract class & hence the below code results in error.
        //NumberFormat currency = new NumberFormat();
        //Another method to make this work:
        NumberFormat currency = NumberFormat.getCurrencyInstance();
        String result = currency.format(12345.678);
        System.out.println(result); //Output > $12,345.68

        //Can also write below stmt as : NumberFormat.getPercentInstance().format(0.1); //method chaining
        NumberFormat perc = NumberFormat.getPercentInstance();
        System.out.println(perc.format(0.1)); //Output > 10%


        //Reading input in Java
        Scanner scan = new Scanner(System.in);
        byte age = scan.nextByte(); //other methods: next, nextLine, nextBool, nextFloat, nextDouble ...
        //next is to input string.
        //nextLine is to input complete line
        System.out.println("Your age: " + age); //Input > 21, Output > Your age: 21

        /*
            System.out.print() :: prints
            System.out.println() :: prints and enter into new line
        */
        String name = scan.nextLine().trim();
        System.out.println("Your name: " + name); // Input > "     DS Rathore", Output > "Your name: DS Rathore"
    }
}