String Class (non-primitive datatype)

String Class:

Syntax:

public final class String

extends Object

implements Serializable, Comparable

Use:

• The String class represents character strings. 
• All string literals in Java programs, such as "abc".

For Example: 

String str="sarthak";

or

char name[] = {'s', 'a', 'r','t', 'h', 'a','k'};

String str = new String(name);

• In java, objects of String are immutable.
• It cannot be changed once created.
• The java.lang.String class provides a lot of methods to work on string.
• we can perform operations on string such as trimming, concatenating, converting, comparing, replacing strings etc.

Constructor:

• String(byte[] byte_arr):
• Construct a new String by decoding the byte array.

Example:

byte[] b = {65, 66, 67};

String s =new String(b);

• String(byte[] byte_arr, int start_index, int length) 
• Construct a new string from the bytes array depending on the arguments.

Example:

byte[] b1 = {65, 66, 67, 68, 69};

String s = new String(b1, 1, 3);

• String(char[] char_arr)
• Allocates a new String from the given Character array

Example:

char name[] = {'s', 'a', 'r','t', 'h', 'a','k'};

String s = new String(name); 

• String(char[] char_array, int start_index, int count)
• Allocates a String from a given character array as per arguments.

Example:

char name[] = {'s', 'a', 'r','t', 'h', 'a','k'};

String sn = new String(name, 1, 3);

• String(StringBuffer s_buffer):
• Allocates a new string from the string in argument.

Example:

StringBuffer sb = new StringBuffer("Sarthak");

String s = new String(sb);

• String(StringBuilder s_builder):
• Allocates a new string from the string in arguments.

Example:

StringBuilder sb1 = new StringBuilder("Sarthak");

String s = new String(sb1);

Methods:

• int length():
• Returns the number of characters

Example:

String s = "Sarthak";

System.out.println(s.length());

• Char charAt(int i):
• Returns the character at ith index

Example:

System.out.println(s.charAt(3));

• String substring (int i):
• Return the substring from the ith  index character to end.

Example:

System.out.println(s.substring(3));

• String substring (int i, int j):
• Returns the substring from i to j-1 index.

Example:

System.out.println(s.substring(1, 3));

• String concat( String str):
• Concatenates specified string.

Example:

String s1="Sarthak";

String s2="Patel";

System.out.println(s1.concat(s2));

• int indexOf (String s):
• Returns the index within the string of the first occurrence

Example:

String s = "I am Student";

int output = s.indexOf("I");

• int indexOf (String s, int i):
• Returns the index within the string of the first occurrence of the specified string as per argument.

Example:

String s = "I am Student";

int output = s.indexOf("t",7);

• Int lastIndexOf(String s): 
• Returns the index within the string of the last occurrence of the specified string.

Example:
String s = "I am Students";
int output = s.lastIndexOf("t");

• boolean equals( Object otherObj):
• Compares this string to the specified object.

Example:
System.out.println("Sarthak".equals("Sarthak"));

• boolean  equalsIgnoreCase (String anotherString): 
• Compares string to another string with ignoring case.

Example:
System.out.println("Sarthak".equalsIgnoreCase("Sarthak"));

• int compareTo( String anotherString):
• Compares two string lexicographically.
• It will return three values:
•  out < 0  // s1 comes before s2
•  out = 0  // s1 and s2 are equal.
•  out > 0   // s1 comes after s2.

Example:
System.out.println("Sarthak".compareTo("Sarthak"));

• String toLowerCase(): 
• Converts all the characters in the String to lower case.

Example:
System.out.println("Sarthak".toLowerCase());

• String toUpperCase(): 
• Converts all the characters in the String to upper case.

Example:
System.out.println("Sarthak".toUpperCase());

• String trim(): 
• Returns the copy of the String, by removing whitespaces at both ends.

Example:
System.out.println(" I am Sarthak ".trim());

• String replace (char oldChar, char newChar): 
• Returns new string by replacing all occurrences of oldChar with newChar.

Example:
System.out.println(" I am Sarthak ".replace('a','b'));

How to create String reference?

Differences: