Java Technology Update

How can you create our own Exception? •       ->If you are creating our own Exception that is known as custom exception or user-defined exception. •       -> Java custom exceptions are used to customize the exception according to user need. •       -> By the help of custom exception, we can have our own exception and message. Let's see a simple example of java custom exception. •       package com.technology4nextvision; •       class technology4nextvision extends RuntimeException •       { •                 private static final long serialVersionUID = 1L; •                 technology4nextvision(String s) •                 { •                          super(s); •                 } •       } •       class technology4nextvisionTest •       { •                 public static void main(String args[]) •                 { •                          String s="technology4nextvision"; •                          •         

Program to find the frequency string in string array (Passing String from command line arguments) package com.myconceptsonjava.practice; import java.util.ArrayList; import java.util.HashMap; import java.util.List; import java.util.Map; public class Test {     public static void main(String[] args) {     Map<String, Integer> m = new HashMap<String, Integer>();     // Initialize frequency table from command line     for (String a : args) {     Integer freq = m.get(a);     m.put(a, (freq == null) ? 1 : freq + 1);     }     System.out.println(m); } } Program to find the frequency string in string array and print them in natural  sorting order (Passing String from command line arguments) package com.myconceptsonjava.practice; import java.util.ArrayList; import java.util.TreeMap; import java.util.List; import java.util.Map; public class Test {     public static void main(String[] args) {     Map<String, Integer> m = new TreeMap<String, Integer>();     // Initia

Why does StringBuffer/StringBuilder not override equals or hashCode? Ans:    Actually behind this everything depends upon hashcode code value. To understand this concept lets take an example : String str1 = new String ( "chandan" ); String str2 = new String ( "chandan" ); HashMap hm = new HashMap () hm . put ( str1 , "hello" ); hm . put ( str2 , "bye" ); final hm: hm = { chandan = bye } In above code, str1 and str2 are two different String objects. It should be added in HashMap ? Answer is  NO . Because before inserting/putting value in HashMap, it internally checks and compare hashCode value of  str1 ,  str2 . Both retun same hascode value because String class override equals() and hashcode() method. So upon executing  hm.put(str2,"bye");  first key will get override with new value. Now try this : StringBuilder sb1 = new StringBuilder ( "chandan" ); StringBuilder sb2 = new StringBuilder (