Java Fundamentals

.java

//Strings
package com.caleb;

public class Main {
    public static void main(String[] args) {
       String hello ="   CALEB" + "MBUGUA!!  ";
       //Concat strings
        //String is a class therefore it has methods we canbe able to access.
        System.out.println(hello.toLowerCase());

    }
}


//Escape sequences
package com.caleb;

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

        String message = "Caleb \"Mbugua\"";

        String url ="c:\\Windows\\...";

        String name ="Mercy \n wanjiru";

        String backslash = "c:\t Windows\\...";

        System.out.println(backslash);

    }
}

//Arrays
package com.caleb;

import java.lang.reflect.Array;
import java.util.Arrays;

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

        int numbers[] = new int[5];

        numbers[0]=0;
        numbers[1]=1;

        //converting an array to string otherwise it returns the memory address
       // Arrays.toString(numbers);

        //Method2
        int numbersTwo[] ={2,3,4,1,5};

        //sort Array
        Arrays.sort(numbersTwo);

        System.out.println(Arrays.toString(numbers));
        System.out.println(numbersTwo.length);
        System.out.println(Arrays.toString(numbersTwo));


    }
}

//2d arrays
package com.caleb;

import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        //2d arrays
        int numbers [][] = new int[2][3];
        numbers [0][0] =1;
        System.out.println(Arrays.deepToString(numbers));

        //method2
        int numbersTwo [][] ={{1,3,5},{8,7,6}};
        System.out.println(Arrays.deepToString(numbersTwo));

    }
}

//CONSTANTS
package com.caleb;

import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        
        final float PI =3.14F;

    }
}

//Augmented Operators
package com.caleb;

public class Main {
    public static void main(String[] args) {
      int x= 1;
      int y =++x;

      //has different meaning with
        int z = x++;
        //increasing with two
        
        int p =x+2;
        
        //Augmented operators
        p+=2;
        
        
      System.out.println(y);
      System.out.println(z);
        System.out.println(p);
    }
}

//Casting
package com.caleb;

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

        //Implicit Casting
        // byte > short > int >long > float > double
        //implicit casting happens whenever we are not going to loose data
        //example (when converting a byte to int)
        double x = 1.1;
        double y = x + 2;

        //Explicit casting
        //You want to convert a big datatype to a small one
        int z = (int) x +2;
        System.out.println(z);
        System.out.println(y);

        //casting incompatible types eg a string ->integer
        /*
        String H = "1";
        int p = Integer.parseInt(H) +2;
        System.out.println(p);
        */

        String c = "1.1";
        Double e = Double.parseDouble(c) +2;
        System.out.println(e);

    }
}

//Math Operations
package com.caleb;

public class Main {
    public static void main(String[] args) {
        /*
        int result = Math.round(1.1F);
        System.out.println(result);
        */
        /*
        int result = (int) Math.ceil(1.1F);
        System.out.println(result);
        */
        /*
        int result = (int) Math.floor(1.1F);
        System.out.println(result);
       */

        /*
        int result = Math.max(1,2);
        System.out.println(result);
        */
        //returns a number between 0-1 by default
        //mutilply by 100 to return larger numbers
        /*
        double result = Math.random()*100;
        System.out.println(result);
        */

        //Rounding off
        int result = (int) Math.round(Math.random()*100);
        System.out.println(result);
    }
}

//Number Format
package com.caleb;

import java.text.NumberFormat;

public class Main {
    public static void main(String[] args) {
        //Number formatting
        // Abstract classes are classes that cannot be instantiated
        //Method overriding(one method repeated or implemented mutiple times

        /*format currency
        NumberFormat currency = NumberFormat.getCurrencyInstance();
        String result= currency.format(12345678.91);
        System.out.println(result);
        */

        //Method chaining
       String result = NumberFormat.getPercentInstance().format(0.1);
        System.out.println(result);
    }
}


//User Input

package com.caleb;


import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        /*
        Scanner scanner = new Scanner(System.in);
        //print prints out everything on the same line unlike println which adds an
        //extra line
        System.out.print("Age:");

        //for reading a float i would say next float
        byte age = scanner.nextByte();
        System.out.println("Your age is" + age + "Years");
        */
        /*Reading a String*/
        /*
        Scanner scanner = new Scanner(System.in);
        System.out.print("Name:");
        String name = scanner.next();
        System.out.println("You are" + name);

         */
        /*next line is much more ideal in  reading strings unlike next which is
        token based and reads the first line*/

        Scanner scanner = new Scanner(System.in);
        System.out.print("Name:");
        //trim is applied to remove the white spaces in the line
        String name = scanner.nextLine().trim();
        System.out.println("You are" + name);

    }
}


//Comparsion Operators
package com.caleb;

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

        //comparison operator
        int x=1;
        int y =2;

        //System.out.println(x<=y);

        //inequality operator
        System.out.println(x != y);

        //others
/* <=2
* */
    }
}

//Logical Operators
package com.caleb;

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

        /*
        AND Operator

        int temperature = 12;
        boolean isWarm = temperature> 20 && temperature <30 ;

        System.out.println(isWarm);
        */

        boolean hasHighIncome = false;
        boolean hasLowCredit = true;
        boolean hasCriminalRecord = false;
        boolean isEligible = (hasHighIncome || hasLowCredit) && !hasCriminalRecord ;

        System.out.println(isEligible);

    }
}


//If Statement
package com.caleb;

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

        int temp = 2;
        if (temp > 30) {
            System.out.println("its a hot day");
            System.out.println("Drink water");
        }
        else if(temp > 20 )
            //braces  are only necessary when i am evaluating multiple statements
            System.out.println("Beautiful day");
        else
            System.out.println("Cold day");

    }
}

//Ternary Operator
package com.caleb;

public class Main {
    public static void main(String[] args) {
        int income = 120_000;
        //if i put a variable within a block i only make it
        //accessible within that block

        //professional way to write code
        boolean hasHighIncome = (income > 190_000);
        System.out.println(hasHighIncome);

        //ternary operator
        String className  = (income > 100_000) ? "Fist Class" : "Economy Class";
        System.out.println(className);
    }
}

//Switch Statement
package com.caleb;

public class Main {
    public static void main(String[] args) {
        String role = "admin";

        switch (role){
            case "admin":
                System.out.println("User is Admin");
                break;
            case "user":
                System.out.println("Normal User");
                break;
            default:
                System.out.println("Unknown");
        }

    }
}


//If Statements Exercise
package com.caleb;

import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Number:");
        int number= scanner.nextInt();

        //always begin with the Most specific condition
        if (number % 3 == 0 && number % 5==0 )
            System.out.println("Fizz Buzz");
        else if (number % 5==0)
            System.out.println("Fizz");
        else if (number % 3 == 0 )
            System.out.println("Buzz");
        else
            System.out.println(number);
    }
}

//for loop

package com.caleb;

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

        for (int i=0; i<5; i++)
            System.out.println("CALEB JAVA");

    }
}

//While Loop
package com.caleb;

import java.util.Scanner;

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

       //while loop is ideal when you do not know how many number of times you will loop through
       /*
        int i=5;
        while (i > 0){
            System.out.println("Hello World" + i);
            i --;
        }
        */
        //While loop example
        Scanner scanner = new Scanner(System.in);
        String input = "";
        while(!input.equals("quit")){
            System.out.print("Input:");
            input = scanner.next().toLowerCase();
            System.out.println(input);
        }


    }
}



//Break and Continue
package com.caleb;

import java.util.Scanner;

public class Main {

    //Once Java encounters the Break it leaves the loop and
    //does not execute anything else

    //Continue statement moves the Control to the beginning of a Loop

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String input = "";
        while(!input.equals("quit")){
            System.out.print("Input:");
            input = scanner.next().toLowerCase();
            if(input.equals("pass"))
                continue;
            if(input.equals("quit"))
                break;
            System.out.println(input);
        }
    }
}