Strings in Java

Strings

• Representing a set of characters altogether,  we can define the data type String is used. For example, Following line declares and initialize a String has an initial value “Welcome to Java” String str = "Welcome to Java";
• String is predefined java class same like System, Scanner etc.
• String is not a primitive data type
• String is a reference type
• A string object is immutable (Mean once object is created, it’s contents are unchange able) For example :
  String str = "Java";
str = "HTML"; 
  
  In the above example : Instead of changing the contents of str, str unrefrenced and updated with a new reference containing “HTML”.
• Interned Strings : JVM uses unique instance to string litrals with the same character sequence to improve and utilize memory efficiently. It also helps to save memory. Result : s1==s2 is false. Using new keyword creates  a new object. s1==s3 is true. using the string initializer and without creating a new object and if the same type of interned object (having same sequence of characters) is already created.

How to get String Length, Characters, and Combine Strings?

• length()     Returns an int value,  have the the total number of characters available in this string
• charAt(int index )   Returns a character of given index from a string
• concat(String str)    Generates a  new string after concatenating the two ( this string with string str)

How to Convert, Replace, and Splitt Strings?

• toLowerCase()     Converts all characters to lowercase and returns a new string
• toUpperCase()    Converts all characters to uppercase and returns a new string
• trim()      Trimms blank character from both sides and return a new string
• replace(char oChar, char nChar)  Replaces all matched character with new characters and returns a new string
• replaceFirst(String oString, String nString)  Replaces the first match substring and returns a new string
• replaceAll(String oString, String nString)  Replace all matched substring from string and return a new string
• split(String delimiter )  Split the substring by the delimeter and returns an array of strings

How to extract Substrings from a String?

• subString(int beginIndex) Returns this string’s substring that begins with the character at the specified beginIndex and extends to the end of the string
• subString(int beginIndex, int endIndex)    Returns this string’s substring that begins at the specified beginIndex and extends to the character at index endIndex – 1. Note that the character at endIndex is not part of the substring.

How to find a Character or a Substring from a String?

• indexOf(char c)  Retruns an int value containing idex of the first occurrence of c in the string otherwise -1 if no match is found in this string
• indexOf(char c, int frmIndex)  Retruns an int value containing index of the first occurrence of c after given idex in the string otherwise -1 if no match is found in this string
• indexOf(String str ) Returns an int containing the index of the first occurence of string in str otherwise -1 if no match is found in this string
• indexOf(String str, int fromIndex) Returns an int value containing the index of the first occurrence of string s in this str after fromIndex otherwise -1 if no match is found in this string
• lastIndexOf(int c) Returns an int value containing  the index of the last occurrence of c in the string otherwise -1 if no match is found in this string
• lastIndexOf( int c, int fromIndex ) Returns an int value containing the index of the last occurrence of c before fromIndex in this string otherwise -1 if no match is found in this string
• lastIndexOf(String s) Returns an int value containing  the index of the last occurrence of string sotherwise -1 if no match  in this string
• lastIndexOf(String s,  int frmIndex ) Returns an int value containing the index of the last occurrence of string s before frmIndex otherwise -1 if no match this string