Array.java

// In this section we learn about te array and arrayList

import java.io.PrintStream;
import java.util.*;

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

        // Array is fixed size and same type value
        int[] array=new int[5]; // So length is 5
        // Another way to writ an array is we know the element and length
        int [] Array={2,56,78,32,56,645,21};
        // So for access by using the index value
        System.out.println(Array[2]);  // Output is 78
        // for updating value or add value
        array[0]=45; array[1]=34; array[2]=32; array[3]=67; array[4]=776;

        // Traversing using For-Each loop only for array in java
        for (int x:array){ System.out.println(x);}
        // Traversing using For loop
        for (int k : Array) {
            System.out.println(k);
        }
           /* So diff bet for-each and for is that in for loop we access by the
           index value and for-each loop we don't  required index value */

        // -- Practice Question Reverse an Array ---

        int[] reverse=new int[Array.length];
        for(int i=Array.length-1,j=0;i>=0;i--){
            reverse[j]=Array[i];
            System.out.println(Array[j]+" "+reverse[j]);
            j++;
        }

    }
}


// --------------------------- Array Finding Second Largest Number  ---------------------------------

class array{
    public  static void main(String[] args){
        int[] Array ={ 100,23,435,45,435};

        int FirstLargest , SecondLargest , ThiredLargest;

        FirstLargest=SecondLargest=Integer.MIN_VALUE; //Set some value to var

        for(int i=0;i<Array.length;i++){
            if (Array[i]>FirstLargest){
                // ThiredLargest=SecondLargest;
                SecondLargest=FirstLargest; // before updating FirstValue Stored it  into SecondValue
                FirstLargest=Array[i];
            } else if ( Array[i]>SecondLargest && Array[i]!=FirstLargest) {
                SecondLargest=Array[i];
            }
        }
        System.out.println("FirstValue: "+FirstLargest);
        System.out.println("SecondValue: "+SecondLargest);
        // System.out.println("ThiredValue: "+ThiredLargest);

    }
}

//  ---------------------------  Reverse  of an Array -----------------------------------

class array{
    public static void main(String[] args){
        int []Array={19,34,21,4345,12,2};
        int []rev=new int[Array.length];
        for (int i=Array.length-1,j=0 ; i>=0 ; i--){
            rev[j]=Array[i];
            System.out.println(rev[j]);
            j++;
        }
    }
}

// --------------------- Increasing the size of an array in java ---------------------------


/*
  In java Once`s array is created it can`t be increased in size . We take a help of one another  reference of array
        Steps
      1) Create another new bigger size of array using diif variable name of old array.
      2) Copying all Element into the new array.
      3) Assign  that old array reference to the new array {oldArray=newArray} and new array to the null.
      4) So that old Array element are in garbage collector
  This is only one way to increasing the size of an array in java . The arrayList follows this method.
 */

class array {
    public static void main(String[] args) {
        int[] Array = {19, 34, 21, 4345, 12, 2};
        int[] New = new int[2 * Array.length]; // New Array
        // copying element
        for (int i = 0; i < Array.length; i++) {
            New[i] = Array[i];  // Copying element
        }

        // Step 3
        Array=New;// old array reference to the new array
        New=null;// array to the null

        // Cheking an size of array

        Array[6]=10;Array[7]=39;
        System.out.println(Array[7]);
        System.out.println(New);

    }
}