Module-7A

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StringBuilder Class:

public class Welcome {

      public static void main(String[] args) {

                  String webName = new String("Hadoop");

                  webName = webName+"Exam";

                  webName = webName+".com";

                  System.out.println(webName);

                 

                  StringBuilder webName1 = new StringBuilder("Hadoop");

                  webName1 = webName1.append("Exam");

                  webName1 = webName1.append(".com");

                  System.out.println(webName1);

                 

                  StringBuilder a = new StringBuilder("Had");

                  StringBuilder b = a.append("oo");

                  b = b.append("p").append("Exam");

                  System.out.println("a=" + a);

                  System.out.println("b=" + b);

            }

}

 

 

-       When we chained String method calls, the result was a new String with the answer. Chaining StringBuilder objects doesn’t work this way. Instead, the StringBuilder changes its own state and returns a reference to itself.

 

-       Size is the number of characters currently in the sequence, and capacity is the number of characters the sequence can currently hold. Since a String is immutable, the size and capacity are the same. The number of characters appearing in the String is both the size and capacity.

 

-       Do hands On your own with all the StringBuilder methods (Which is quite similar to String methods)

 

equal method and == operator

 

public class Welcome {

      public static void main(String[] args) {

 

            String name;

            Welcome t1 = new Welcome();

            Welcome t2 = new Welcome();

            Welcome t3 = t1;

            System.out.println(t1 == t1); // true

            System.out.println(t1 == t2); // false

            System.out.println(t1.equals(t2)); // false

 

      }

}

 

 

Arrays in Java:

 

public class Welcome {

      public static void main(String[] args) {

 

            String[] str = new String[]{"Hadoop","Exam",".com"}; //String array

            System.out.println("Length of str array : "+ str.length);

           

            String[] str1 = new String[5];

            System.out.println("Default values in String array : "+ str1[3]);

           

            int[] values = new int[10];

            System.out.println("Length of int array : "+ values.length);

            System.out.println("Default values in int array : "+ values[5]);

      }

}

 

public class Welcome {

      public static void main(String[] args) {

 

            int[] values = {1,2,3}; //anonymous array

           

            //Below all 4 are equals

            int[] val1;

            int [] val2;

            int val3[];

            int val4 [];

           

            //Another way

            int val5[] , val6; //Here val5 is integer array and val6 is int variable

      }

}

public class Welcome {

 

      String welcomeMessage;

     

      Welcome(String message){

            welcomeMessage=message;

      }

      public static void main(String[] args) {

 

            Welcome[] welcomeArray = new Welcome[]{ new Welcome("HadoopExam"), new Welcome("QuickTechie") };

            System.out.println(welcomeArray.length);

            System.out.println(welcomeArray[0].welcomeMessage);

            System.out.println(welcomeArray[1].welcomeMessage);

           

            for(int i=0;i<welcomeArray.length;i++){

                  System.out.println("Welcome to "+welcomeArray[i].welcomeMessage);

            }

           

      }

}

 

 

Sorting Array Elements

 

import java.util.Arrays;

public class Welcome {

      public static void main(String[] args) {

 

            int[] values = new int[]{6,3,7,1,4};

            Arrays.sort(values);

            for(int i=0;i<values.length;i++){

                  System.out.println(values[i]);

            }

           

            String[] str = new String[]{ "100" , "102" ,"10", "91"};

            Arrays.sort(str);

            for(int i=0;i<str.length;i++){

                  System.out.println(str[i]);

            }

      }

}

 

Element Searching: Java also provides a convenient way to search - but only if the array is already sorted.

 

Binary search rules:

 

import java.util.Arrays;

public class Welcome {

      public static void main(String[] args) {

 

            int[] numbers = {2,4,6,8};

            System.out.println(Arrays.binarySearch(numbers, 2)); // 0

            System.out.println(Arrays.binarySearch(numbers, 4)); // 1

            System.out.println(Arrays.binarySearch(numbers, 1)); // -1

            System.out.println(Arrays.binarySearch(numbers, 3)); // -2

            System.out.println(Arrays.binarySearch(numbers, 9)); // -5

           

            int[] numbers1 = new int[] {3,2,1};

            System.out.println(Arrays.binarySearch(numbers1, 2));

            System.out.println(Arrays.binarySearch(numbers1, 3));

      }

}

 

Multidimensional Array: Array of Array

 

public class Welcome {

      public static void main(String[] args) {

 

            int[][] intArray1; // 2D array

            int intArray2 [][]; // 2D array

            int[] intArray3[]; // 2D array

            int[] intArray4 [], space [][]; // a 2D AND a 3D array

           

           

            int[][] value1 = new int[][]{{1,2,3} , {4,5,6} , {7,8}};

            for(int i=0;i<value1.length ; i++){

                  for(int j=0;j<value1[i].length ; j++){

                        System.out.println(value1[i][j]);

                  }

            }

           

            //Another way to declare array

            int [][] values = new int[4][];

            values[0] = new int[5];

            values[1] = new int[3];

      }

}