Strings Data Structure and Numbers
- Strings are defined as an array of characters.
- The difference between a character array and a string is the string is terminated with a special character
\0
- In java, objects of String are immutable which means a constant and cannot be changed once created
Some of constructor functions for Strings
String(byte[] byte_arr)
String(char[] char_arr)
String(char[] char_array, int start_index, int count)
String(StringBuffer s_buffer)
String(StringBuilder s_builder)
Methods in java.util.String
Class
Methods |
Description |
Returns |
Notes |
length |
Returns the number of characters in the String |
int |
|
charAt(int i) |
Returns the character at ith index |
Char |
|
substring(int i) |
Return the substring from the ith index character to end |
String |
|
substring(int i, int j) |
Returns the substring from i to j-1 index |
String |
|
concat(String str) |
Concatenates specified string to the end of this string |
String |
|
indexOf(String str) |
Returns the index within the string of the first occurrence of the specified string |
int |
If not present will return -1 |
indexOf(String str, int i) |
Returns the index within the string of the first occurrence of the specified string, starting at the specified index |
int |
|
lastIndexOf(String str) |
Returns the index within the string of the last occurrence of the specified string |
int |
|
equals(String s) |
Compares this string to the specified string |
boolean |
|
equalsIgnoreCase(String s) |
Compares string to another string, ignoring case considerations |
boolean |
|
toLowerCase(String s) |
Converts all the characters in the String to lower case |
String |
|
toUpperCase(String s) |
Converts all the characters in the String to upper case |
String |
|
trim |
Returns the copy of the String, by removing whitespaces at both ends. It does not affect whitespaces in the middle |
String |
|
replace(char oldChar, char newChar) |
Returns new string by replacing all occurrences of oldChar with newChar |
String |
|
- Some other methods are
- compareTo(String s)
- compareToIgnoreCase(String s)
Methods in java.util.Character
Class
Methods |
Description |
Returns |
Notes |
isLetter(char c) |
This method is used to determine whether the specified char value(ch) is a letter or not |
boolean |
only within [A-Za-z] |
isDigit(char c) |
This method is used to determine whether the specified char value(ch) is a digit or not |
boolean |
|
isWhitespace(char c) |
It determines whether the specified char value(ch) is white space |
boolean |
|
- Some other methods are
- isUpperCase(char c)
- toUpperCase(char c)
- isLowerCase(char c)
- toLowerCase(char c)
String s = “Random String”;
String s = new String (“Random String”);
- Replace non-alphanumeric characters within String
s.replaceAll("[^A-Za-z0-9]", "");