Update readme.md

String/readme.md

@@ -4,6 +4,8 @@ Strings in Java are Objects that are backed internally by a char array.
 Since arrays are immutable(cannot grow), Strings are immutable as well. 
 Whenever a change to a String is made, an entirely new String is created. 
 
+String is a sequence of characters. In java, objects of String are immutable which means a constant and cannot be changed once created.
+
 ### what is mean by the <a href = "https://www.programiz.com/java-programming/examples/create-immutable-class">Immutable</a> ?
 
 Syntax:
@@ -30,4 +32,33 @@ Example:
 String str = new String(str);
 ```
 
+# Interfaces and classes in java string
+1. CharBuffer
+2. String
+   String is a sequence of characters. In java, objects of String are immutable which means a constant and cannot be changed once created.
+  - There is a two to create string-
+    - String Literals
+    - Using new keywords
+3. StringBuffer
+
+4. StringBuilder
+   The StringBuilder in Java represents a mutable sequence of characters. Since the String Class in Java creates an immutable sequence of characters, the              StringBuilder class provides an alternate to String Class, as it creates a mutable sequence of characters.
+   
+   syntax:
+   ```java
+   StringBuilder str = new StringBuilder();
+   str.append("GFG");
+   ```
+5. StringTockenizer
+   StringTokenizer class in Java is used to break a string into tokens. 
+   
+   syntax:
+   ```java
+   
+   ```
+
+
+
+ 
+