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

Every java defined class is overriding equals and hashCode method of the object class. Equals method provides the way to equate 2 string objects.. If you see the implementation of equals method of String class, you will find character by character matching of string characters... hashCode method of Object class is a native method.. hashCode implemetation provides the way to reach the specified object on heap.. read less

Java allows two ways to compare objects. 1) equals 2) ==. Both are different and in case of String, its very much different. Two string needs to be compared based on equals and hashcode method meaning there state is same i.e. there value and not just where the pointer is in the heap space allocated by java. String class does not give dfeault implementations for equals and hashcode and hence we need to override it. Equals and hashcode also leads to faster searching where hashing method is used for searching e.g. collection classes. read less

We may come across the requirement to check for object equality. To check whether both objects contains same properties value or not. This can be done by override the Equals method. While overriding the Equals method, you should consider the followings If object argument is null, return false If type of object argument is different than type of this, return false If object argument is neither null nor its type is different check for the values of the instance fields. If they are equal return true else return false read less