why string class is override in euals()/ hashCode Hethods?

• In the above program we compared two string using equals() method and it returns true.and comparing using == operator returns false. • Basically equal() will also return false on comparing those two strings because default functionality of equal() method is to compare references and two strings are created using new operator so both references are different. • But String class overriding equals() method and in that equals method it comparing content of the strings and returning true if both are having same content false if not. • Lets see what happen if we compare two stringBuffer objects using equals() method. • package com.instanceofjava; • • class StringBufferEqualsDemo{ • • public static void main(String [] args){ • • StringBuffer fstr= new StringBuffer("Javatutorials"); • StringBuffer sstr= new StringBuffer("Javatutorials"); • • System.out.println(fstr.equals(sstr)); • System.out.println(fstr==sstr); • • System.out.println(fstr.hashCode()); • System.out.println(sstr.hashCode()); • } • } OUTPUT • false • false • 1704856573 • 705927765 • If you observe above java program when we are comparing two stringBuffer objects equal() method returning false even content is same. Because StringBuffer class not overriding equals() and hashcode() methods. • StringBuilder is also not overriding equals() method? lets see a program and clarify. • • package com.instanceofjava; • • class StringBuilderEqualsDemo{ • • public static void main(String [] args){ • • StringBuilder fstr= new StringBuilder("Javatutorials"); • StringBuilder sstr= new StringBuilder("Javatutorials"); • • System.out.println(fstr.equals(sstr)); • System.out.println(fstr==sstr); • • System.out.println(fstr.hashCode()); • System.out.println(sstr.hashCode()); • } • } OUTPUT 1. false 2. false 3. 1704856573 4. 705927765 5. So now its cleared that StringBuffer and StringBuilder classes not overriding equals() and hashCode() methods. 6. But Why? 7. Why StringBuffer and StringBuilder classes not overriding equals() method and hashcode() method where as String class is overriding these two methods. 8. Basically Strings are Immutable means Whenever we try to change the value of string result will be new string. So string content wont change. 9. StringBuffer main use is mutable means when we append a string to it it will add to existing object. 10. When the content changes the hashcode will changes. 11. Lets see a program on adding elements to hashmap. read less